edition 2020-21 power electronics

Edition 2020-21

Power Electronics PEN-Drive / G-Drive Course & LIVE Classroom Program Workbook

Electrical Engineering Electrical & Electronics Engineering

GATE / ESE / PSUs

Power Electronics PEN-Drive / G-Drive Course & LIVE Classroom Program

Workbook

EE / EEE

Copyright © All Rights Reserved

GATE ACADEMY ®

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Edition : 2020-21

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GATE Syllabus Characteristics of semiconductor power devices: Diode, Thyristor, Triac, GTO, MOSFET, IGBT; DC to DC conversion: Buck, Boost and Buck-Boost converters; Single and three phase configuration of uncontrolled rectifiers, Line commutated thyristor based converters, Bidirectional ac to dc voltage source converters, Issues of line current harmonics, Power factor, Distortion factor of ac to dc converters, Single phase and three phase inverters, Sinusoidal pulse width modulation.

ESE Syllabus Semiconductor power diodes, transistors, thyristors, triacs, GTOs, MOSFETs and IGBTs - static characteristics and principles ofoperation, triggering circuits, phase control rectifiers, bridge converters - fully controlled and half controlled, principles of choppers and inverters, basis concepts of adjustable speed DC and AC drives, DC-DC switched mode converters, DC-AC switched mode converters, resonant converters, high frequency inductors and transformers, power supplies.

Table of Contents Sr. Chapter Pages

1. Power Semiconductor Switching Devices …………..…..…. 1

2. Single Phase AC to DC Converter …………………………….…. 14

3. Three Phase AC to DC Converter ………….…………..…....…. 29

4. Chopper (DC to DC Converter) ….………..…..…….…..…..…. 35

5. Commutation Techniques …………………..…………………..…. 46

6. Inverter (DC to AC Converter) …………..…………..…..…..…. 51

7. AC Voltage Regulator …………………………..………..…..…..…. 62

Video Lecture Information

Sr. Lecture Name Duration

0 How to study Power Electronics 0:20:13

Power Semiconductor Switching Devices

1 Introduction of Power Electronics 0:31:09

2 Basic Concept of Semiconductor 0:39:34

3 Forward & Reverse Biasing of PN Junction 0:16:32

4 THYRISTOR (SCR) 0:18:00

5 Thyristor PDF

6 Concept of Latching and Holding Current 0:20:00

7 Question Based on Latching and Holding Current 0:40:00

8 Power Diode 0:31:52

9 Operating Modes of SCR 0:47:14

10 Turn on Method of SCR 0:54:05

11 Switching Characteristics of SCR 0:37:36

12 Basic Concept of Commutation Failure 0:22:47

13 Gate Cathode Characteristics 0:24:27

14 Question Based on Gate Cathode Characteristics 0:37:32

15 Types and Modes of Switches 0:34:38

16 Modes of Different Switches 0:40:21

17 Question Based on Different Mode of Switches 0:22:44

18 Switching and Conduction Losses 1:00:51

19 Question Based on Switching Losses 0:40:24

20 Protection of Thyristor 0:49:37

21 Theory of Snubber Circuit 0:42:48

22 Design Considerations of Snubber Circuit 0:28:31

23 Thermal Protection of SCR 0:17:28

24 Series and Parallel Combination 0:51:03

25 Question Based on Series and Parallel Combination 0:35:28

Single Phase Rectifier (AC to DC Converter)

1 Introduction of Rectifier 0:39:26

2 Single Phase Uncontrolled HWR (01) 0:37:12








10 Workbook Q. 1 - Q. 4 0:25:27

11 Workbook Q. 5 0:17:09


13 Workbook Q. 6 - Q. 9 0:17:23

14 Single Phase Controlled HWR (01) 0:40:14

15 Workbook Q.10 0:09:02


17 Workbook Q.11 - Q.12 0:14:06




21 Workbook Q.13 - Q.14 0:16:56

22 Why high value of power factor is required? 0:13:42

23 Single Phase Uncontrolled FWR (01) 0:44:48

24 Single Phase Uncontrolled FWR (02) 0:54:30

25 Workbook Q.15 - Q.16 0:17:20

26 Single Phase Controlled FWR (01 & 02) 0:57:21

27 Single Phase Controlled FWR (03) 0:24:04

28 Single Phase Controlled FWR (04) 1:12:28

29 Input Performance parameters of Single Phase full converter 1:08:35

30 Workbook Q.17 - Q.23 0:27:10

31 Workbook Q.24 - Q.26 0:18:23

32 Workbook Q.27 - Q.29 0:21:17

33 Workbook Q.30 0:13:39

34 Single Phase Controlled FWR (RE Load) 0:31:03

35 Single Phase Controlled FWR (RLE Load) 0:17:58

36 Single Phase Controlled FWR (RL-RLE Load with FD) 0:21:37

37 Special Case of Single Phase full Converter 0:18:52

38 Workbook Q.31 0:16:22

39 Single Phase Half Controlled Bridge Converter (Semi Converter) 01 0:48:31

40 Single Phase Half Controlled Bridge Converter (Semi Converter) 02 0:43:54

41 Input Performance Parameters of Semi Converter 0:24:49

42 Workbook Q.32-Q.33 0:21:23

43 Workbook Q.34 0:14:58

44 Workbook Q.35-Q.36 0:11:41

45 Effect of Source Inductance (01) 1:13:25

46 Effect of Source Inductance (02) 0:45:50

47 Workbook Q.37-Q.38 0:11:46

48 Dual Converter (b) PDF

Three Phase Rectifier (AC to DC Converter)

1 Classification of Rectifier Based on Pulse No 0:17:06

2 Concept of Phase and Line Voltage 0:29:15

3 3 Phase Uncontrolled HWR 0:26:43

4 M-3 Converter with R Load 0:46:53

5 Question Based on Common Anode Configuration 0:14:57

6 M-3 Converter (Continuous Conduction Ripple free Load Current) 0:57:21

7 Question Based on M-3 Converter 0:36:48

8 3 Phase Controlled Bridge Rectifier (B-6 Converter) 1:30:17

9 B-6 Converter (Continuous Conduction Ripple free Load Current) 0:31:27

10 Circuit Turn-off Time in M-3 Converter 0:26:55

11 Workbook Q.1 - Q.3 0:12:01

12 Workbook Q.4 - Q.7 0:09:50

13 Workbook Q.8 - Q.19 0:42:16

14 Workbook Q.20 - Q.23 0:19:59

15 Workbook Q.24 - Q.25 0:16:01

16 Comparison Between 1-Phase & 3-Phase Bridge Converter 0:39:57

17 Workbook Q.26 - Q.28 0:09:57

18 Workbook Q.29 0:09:16

19 3-Phase Semiconverter 0:54:49

20 Source Current Waveform of 3-Phase Semiconverter 0:18:43

21 Comparison Between Semi-Converter and Full Converter PDF

22 Workbook Q.30 0:09:26

23 Important Result for p-pulse Converter PDF

24 Workbook Q.31 - Q.32 0:07:44

25 Workbook Q.33 - Q.35 0:21:18

Chopper (DC to DC Converter)

1 Introduction of Chopper 0:10:36

2 Chopper (DC-DC Converter) PDF

3 Ideal Step Down Chopper 0:51:48

4 Practical Step Down Chopper 0:17:50

5 Step Down Chopper with RLE Load (Part 1) 0:49:31

6 Step Down Chopper with RLE Load (Part 2) 0:33:19

7 Workbook Q.1 - Q.4 0:11:52

8 Workbook Q.5 - Q.7 0:08:33

9 Workbook Q.8 - Q.9 0:25:05

10 Workbook Q.10 0:12:48

11 Workbook Q.11 - Q.12 0:16:03

12 Workbook Q.13 - Q.16 0:12:55

13 Workbook Q.17 - Q.18 0:06:40

14 Discontinuous Conduction in Step Down Chopper 0:27:19

15 Workbook Q.19 - Q.23 0:06:47

16 Workbook Q.24 - Q.28 0:13:39

17 Workbook Q.29 - Q.32 0:09:54

18 Step-up Chopper 0:39:42

19 Workbook Q.33 - Q.35 0:08:34

20 Workbook Q.36 - Q.38 0:08:53

21 Workbook Q.39 0:26:21

22 Classification of Chopper 0:46:04

23 Workbook Q.40 (Type B Chopper) 0:09:42

24 Buck Regulator (Converter) 01 0:44:57

25 Buck Regulator (Concept of Critical Inductance & Capacitance) 02 0:11:43

26 Workbook Q.41 - Q.42 0:18:29

27 Workbook Q.43 - Q.45 0:18:09

28 Boost Regulator (Converter) 0:51:28

29 Workbook Q.46 - Q.48 0:11:55

30 Workbook Q.49 - Q.51 0:25:16

31 Buck-Boost Regulator (Converter) 0:54:09

32 Workbook Q.52 - Q.53 0:19:59

33 Workbook Q.54 - Q.55 0:07:38

34 Workbook Q.56 - Q.58 (Part 1) 0:26:28

35 Workbook Q.59 - Q.61 (Part 2) 0:32:08

36 Workbook Q.62 (Multiphase Buck Converter) 0:16:10

Commutation Techniques

1 Introduction of Commutation 0:24:24

2 Forced Commutation (Class A Commutation) 0:17:47

3 Concept of Load Commutation in LC Circuit 0:46:01

4 Class D Commutation (Voltage Commutation) 1:02:48

5 Workbook Q.1 - Q.4 0:16:02

6 Workbook Q.5 - Q.12 0:14:15

7 Current Commutated Chopper (Class B Commutation) 0:55:34

8 Workbook Q.13 0:08:40

9 Workbook Q.14 - Q.15 0:10:51

10 Class C commutation PDF

Inverter (DC to AC Converter)

1 Introduction of Inverter 0:56:43

2 Single Phase Half Bridge VSI (01) 0:28:17



5 Workbook Q.1 - Q.11 0:23:20

6 Single Phase Full Bridge VSI (01) 0:36:09



9 Workbook Q.12 - Q.17 0:14:54

10 Workbook Q.18 - Q.19 0:17:57

11 Workbook Q.20 - Q.23 0:11:41

12 Workbook Q.24 - Q.29 0:28:22

13 Workbook Q.30 0:15:50

14 Three Phase VSI (180 Degree Conduction Mode) 1:30:38

15 Workbook Q.31 - Q.33 0:16:04

16 Workbook Q.34 - Q.36 0:09:35

17 Three Phase VSI (120 Degree Conduction Mode) 0:59:45

18 Workbook Q.37 - Q.45 0:39:12

19 Pulse width Modulation (Single PWM) 0:42:22

20 Workbook Q.46 - Q.50 0:18:37

21 Workbook Q.51 0:19:05

22 Multiple PWM (M-PWM) 0:25:35

23 Workbook Q.52 - Q.57 0:08:57

24 Sinusoidal Pulse Width Modulation (Bipolar) 0:50:36

25 Sinusoidal Pulse Width Modulation (Unipolar) 0:20:16

26 Workbook Q.58 0:17:36

27 Workbook Q.59 0:14:22

28 Workbook Q.60 - Q.61 0:13:01

29 Workbook Q.62 0:16:02

AC Voltage Regulator

1 AC Voltage Regulator PDF

Chapter 1

Power Semiconductor Switching Devices

Objective & Numerical Ans Type Questions :

Q.1 Consider SCR circuit with latching current of 100 mA shown in figure.

The minimum pulse width (in sec) required for

turn-on the SCR is ________ Q.2 Consider SCR circuit with latching current of

100 mA shown in figure.

The minimum pulse width (in sec) required for

turn-on the SCR is ________ Q.3 An SCR having a turn ON time of 5 sec ,

latching current of 50 mA and holding current of 40 mA is triggered by a short duration pulse and is used in the circuit shown in fig. The minimum pulse width required to turn the SCR ON will be

[GATE 2006, IIT-Kharagpur]

(A) 251 sec (B) 150 sec

(C) 100 sec (D) 5 sec Q.4 The SCR in the circuit shown has a latching

current of 40 mA. A gate pulse of 50μs is

applied to the SCR. The maximum value of R in to ensure successful firing of the SCR is _________. [GATE 2014, IIT-Kharagpur]

. Common Data Questions for 5 to 7 :

In given circuit the thyristor is gated with a pulse width of 40 microsec. The latching current of thyristor is 36 mA.

Q.5 For a load of 20R and 2 HL in series the

current through thyristor is _____ mA.

Q.6 For above case thyristor will turn ON. [Yes/No]

Q.7 To make turn ON, a resistance is connected across load. Its magnitude will be _______ k .

Q.8 The voltage ( sv ) across and the current ( si )

through a semiconductor during a turn-ON transition are shown in figure. The energy dissipated during the turn-ON transition, in mJ, is _________. [GATE 2016, IISc Bangalore]

100 V L = 0.1 H

SCR

100 V

L = 0.1 H

SCR

R = 10

20

0.5 H

100 V 5 k

R100 V

500

200 mH

SCR

300V

60

2 H

Power Electronics [Workbook] 2 GATE ACADEMY®

Q.9 For SCR the gate cathode characteristic has a

straight line of slope of 140 . For trigger source voltage of 20 V and allowable gate power dissipation of 0.5 watts, what is the gate source resistance ? [ESE 2009]

(A) 200 (B) 255

(C) 195 (D) 185

. Common Data Questions for 10 & 11 :

A 1 : 1 pulse transformer (PT) is used to trigger the SCR in the adjacent figure. The SCR is rated at 1.5 kV, 250 A with 250mA,LI 150mA,HI

and max 150mA,GI min 100mA.GI The SCR is

connected to an inductive load, where L = 150 mH in series with a small resistance and the supply voltage is 200 V dc. The forward drops of all transistors/diodes and gate – cathode junction during ON state are 1.0 V.

[GATE 2007, IIT-Kanpur]

Q.10 The value of resistance R should be (A) 4.7 k (B) 470

(C) 47 (D) 4.7

Q.11 The minimum approximate volt-second rating of the pulse transformer suitable for triggering the SCR should be : (volt – second rating is the maximum of product of the voltage and the width of the pulse that may be applied)

(A) 2000μV-s (B) 200μV-s

(C) 20μV-s (D) 2.0μV-s

Q.12 The triggering circuit of a thyristor is shown in fig. The thyristor requires a gate current of 10 mA, for guaranteed turn-on. The value of R required for the thyristor to turn-on reliably under all conditions of bV variation is

[GATE 2004, IIT-Delhi]

(A) 10000 (B) 1600

(C) 1200 (D) 800 Q.13 If the amplitude of the gate pulse to thyristor is

increased, then [IES 1998] (A) Both delay time and rise time would increase. (B) The delay time would increase but the rise

time would decrease (C) The delay time would decrease but the rise

time would increase (D) The delay time would decrease while the rise

time remains unaffected. Q.14 The turn-on time for an SCR is 30 s . The pulse

train at the gate has a frequency of 2.5 kHz with a mark/space ratio of 0.1. This SCR will

(A) turn-on (B) not turn-on (C) turn-on if pulse-frequency is increased (D) turn-on if pulse-frequency is decreased Q.15 When a thyristor gets turned on, the gate drive (A) Should not be removed as it turns off the SCR. (B) Should be removed in order to avoid

increased losses and higher junction temperature

600V

sv

si

0

0

50A

100 A

1 1 sT 2 1 sT

t

t

RPT

10 V

CEV

1.0

200 V

SCR L

100 V

Load

R

12 4 VbV

GATE ACADEMY® 3 Power Semiconductor Switching Devices

(C) May or may not be removed

(D) Gate drive has no relation with the turn on process.

Q.16 The turn on time of an SCR in series with RL circuit can be reduced by

(A) Increasing circuit resistance R

(B) Decreasing R

(C) Increasing Z

(D) Decreasing L


For an SCR, gate-cathode characteristic is given by 1 10g gV I . Gate source voltage is a

rectangular pulse of 15 V with 20 sec duration.

For an average gate power dissipation of 0.3 W and a peak gate-drive power of 5 W.

Q.17 The resistance to be connected in series with the SCR gate is

(A) 11.24 (B) 22.24

(C) 33.24 (D) 43.24

Q.18 The triggering frequency is

(A) 1 kHz (B) 2 kHz

(C) 3 kHz (D) 4 kHz

Q.19 The duty cycle of the triggering pulse is

(A) 0.03 (B) 0.04

(C) 0.05 (D) 0.06

Q.20 A MOSFET rated for 15 A, carries a 10 A periodic current as shown in figure. The ON state resistance of the MOSFET is 0.15 . The average

ON state loss in the MOSFET is

[GATE 2004, IIT-Delhi]

(A) 33.8 W (B) 15.0 W

(C) 7.5 W (D) 3.8 W

Q.21 The snubber circuit is used in thyristor circuits for [IES 2001]

(A) Triggering (B) dv

dt protection

(C) di

dt protection (D) Phase shifting

Common Data Questions for 22 to 24 :

The trigger circuit of a thyristor has a source voltage of 15 V and the load line has a slope of

120 per ampere. The minimum gate current to turn-on the SCR is 25 mA. And average power dissipation of 0.4 W.

Q.22 The value of source resistance required in the gate circuit is _____

Q.23 The trigger voltage is _____ V

Q.24 The trigger current is _____ mA

Q.25 In a thyristor, di

dtprotection is achieved by the use

of [IES 2005]

(A) An inductance L in series with the thyristor

(B) A resistor in series with the thyristor

(C) RC in series with the thyristor

(D) RL in series with the thyristor

Q.26 The source voltage is 100 V and the load resistance is 10 ohm. The SCR can with stand a dv

dt value of 50 v/μsec. If the snubber discharge

current must be limited to 2A. The value of the snubber resistor and capacitor is

(A) 150 , 0.6 F (B) 100 , 0.4 F

(C) 50 , 0.2 F (D) 25 , 0.1 F

Q.27 A power diode is in the forward conduction mode and the forward current is now decreased. The reverse recovery time of the diode is rt and

the rate of fall of the diode current is .di

dt The

stored charge is [IES 2004]

(A) . r

dit

dt

(B) 21.

2 r

dit

dt

(C) 2. r

dit

dt

(D) 1.

2 r

dit

dt

0

10 A

t

R

sV

LR

SCR

C


Q.28 The maximum values of the di/dt and dv/dt for SCR in the following circuit will be

(A) 1.76A / sec, 26.4V / sec

(B) 1.76A / sec,16.4V / sec

(C) 2.76A / sec,16.4V / sec

(D) 2.76A / sec,26.4 V / sec

Q.29 The figure shows the voltage across a power semiconductor device and the current through the device during a switching transitions. Is the transition a turn ON transition or a turn OFF transition? The energy lost during the transition will be [GATE 2005, IIT-Bombay]

(A) Turn ON, 1 2( )2

VIt t

(B) Turn OFF, 1 2( )VI t t

(C) Turn ON, 1 2( )VI t t

(D) Turn OFF, 1 2( )2

VIt t

. Common Data Questions for 30 & 31 :

For a thyristor, maximum junction temperature is 0125 C . The thermal resistance for the thyristor-

sink combination are 0.16jc and 00.08 C / WCS .

Q.30 For a heat- sink temperature of 070 C , the total

average power loss in the thyristor-sink combination will be

(A) 129.17 W (B) 229.17 W

(C) 329.17 W (D) 429.17 W

Q.31 In case heat sink temperature is brought down to 060 C by forced cooling, the percentage increase

in the device rating will be

(A) 5.71 % (B) 6.71 %

(C) 7.71 % (D) 8.71 %

Q.32 A 100 Amp SCR is to be used in parallel with a 150 Amp SCR. The on state voltage drops of the SCRs are 2.1 V and 1.75 V respectively.

The series resistance that should be connected with each SCR if the SCRs have to share the total current of 250 Amp in proportion to their ratings will be

(A) 0.005 (B) 0.006

(C) 0.007 (D) 0.008 Q.33 In a commutation circuit employed to turn off an

SCR, satisfactory turn-off is obtained when

[GATE 1998, IIT Delhi]

(A) Circuit turn-off time < device turn-off time

(B) Circuit turn-off time > device turn-off time

(C) Circuit time constant > device turn-off time

(D) Circuit time constant < device turn-off time

Q.34 The 800 V, 500 A SCRs are to be used in a power circuit having rating of 7.5 kV and 1000 Amp. The no. of series and parallel connected SCRs if the derating factor is 10%, will be

(A) 4, 3 (B) 3, 4

(C) 11, 3 (D) 3, 11

Q.35 It is required to operate 250-A SCR in parallel with 350-A SCR with their respective on-state voltage drops of 1.6 V and 1.2 V. ______ is the value of resistance to be inserted in series with each SCR so that they share the total load of 600 A in proportion to their current ratings.

Q.36 Two thyristors are connected in series as shown in below figure. The supply voltage is 5 kV. Two equal capacitors 1C and 2C each of 0.1 F are

connected across each thyristor, for dynamic voltage sharing. The voltage imbalance across the two thyristors during turn off will be ______. The leakage currents of the thyristors are 15 and 20 mA respectively where as the whole storage charge is 40 C and 30 C respectively for the

thyristors 1 and 2.

2 440sin 314t

250 H

15 0.1 F

0

vV

I

tt1 t2


(A) 2450 V, 2550 V (B) 1450 V, 1550 V

(C) 2450 V, 2450 V (D) 1450 V, 1450 V

Common Data Questions for 37 to 39 :

A string of four series-connected thyristors is provided with static and dynamic equalizing circuits. This string has to withstand an off-state voltage of 10 kV. The static equalizing resistance is 25000 and the dynamic equalizing circuit has

40CR and 0.8μFC . The leakage currents

for four thyristors are 21 mA, 25 mA, 18 mA and 16 mA respectively.

Q.37 The number of the thyristor which shares maximum voltage is _____

Q.38 The maximum voltage shared by any one of thyristor is _____ kV.

Q.39 The maximum discharging current is _____ A.

Q.40 Figure shows four electronic switches (i), (ii), (iii) and (iv). Which of the switches can block voltages of either polarity (applied between terminals “a” and “b”) when the active device is in the OFF state? [GATE 2014, IIT-Kharagpur]

(A) (i), (ii) and (iii) (B) (ii), (iii) and (iv)

(C) (ii) and (iii) (D) (i) and (iv)

Q.41 Figure shows a composite switch consisting of a power transistor (BJT) in series with a diode. Assuming that the transistor switch and the diode are ideal, the I-V characteristic of the composite switch is [GATE 2010, IIT-Guwahati]

(A)

(B)

(C)

(D)

Q.42 Match the switch arrangements on the top row to

the steady-state V-I characteristics on the lower row. The steady state operating points are shown by large black dots. [GATE 2009, IIT-Roorkee]

A.

(I)

B.

(II)

1 0.1 FC

2 0.1 FC

1T

2T

+

–

a

b

a

b(ii)

a

b(iii)

a

b(iv)

V

I

V

I

V

I

V

I

V

I

si

sv

si

sv


C.

(III)

D.

(IV)

(A) A-I B-II C-III D-IV

(B) A-II B-IV C-I D-III

(C) A-IV B-III C-I D-II

(D) A-IV B-III C-II D-I

Q.43 An electronic switch S is required to block voltages of either polarity during its OFF state as shown in the fig (a). This switch is required to conduct in only one direction during its ON state as shown in the figure (b).

[GATE 2005, IIT Bombay]

Which of the following are valid realizations of

the switch S ?

(P)

(Q)

(R)

(S)

(A) Only P (B) P and Q

(C) P and R (D) R and S

Q.44 Figure shows a MOSFET with an integral body diode. It is employed as a power switching device in the ON and OFF states through appropriate control. The ON and OFF states of the switch are given on the DS sV I plane by

[GATE 2003, IIT Madras]

(A)

(B)

(C)

(D)

si

sv

si

sv

1 1'

S

1 1'S

i

(a)

(b)

1 1'

1 1'

1 1'

1 1'

DSV

S

D

G

SI

SI

DSV

SI

DSV

SI

DSV

SI

DSV


Q.45 An SCR has half cycle surge current of rating-of 3000 A for 50 Hz supply. One cycle surge current rating will be [IES 1999]

(A) 1500 A (B) 2121.32 A

(C) 4242.64 A (D) 6000 A

Q.46 A series string of three SCRs shown in below figure is designed to withstand an off state voltage of 4 kV. The static equalising resistor

20kSR , 20DR and 0.1 FC . Estimate

the voltage across 2SCR at the time of turn off.

The whole storage charge for 1SCR 140 C ,

2SCR 150 C and 3SCR 130 C .

(A) 1133.3 V (B) 2233.3 V

(C) 1233.3 V (D) 1483.3 V

Q.47 For the power semiconductor devices IGBT, MOSFET, Diode and Thyristor, which one of the following statements is TRUE?

[GATE 2017, IIT Roorkee]

(A) All the four are majority carrier devices.

(B) All the four are minority carrier devices.

(C) IGBT and MOSFET are majority carrier devices, whereas Diode and Thyristor are minority carrier devices.

(D) MOSFET is majority carrier device, whereas IGBT, Diode Thyristor are minority carrier devices.

Q.48 A steady dc current of 100 A is flowing through a power module (S, D) as shown in Figure (a). The V-I characteristics of the IGBT (S) and the diode (D) are shown in Figures (b) and (c), respectively. The conduction power loss in the power module (S, D), in watts, is ________.

[GATE 2016, IISc Bangalore]

Practice (objective & Num Ans) Questions :

Q.1 The latching current of SCR in the below circuit is 4mA. The minimum width of the gate pulse required to turn on the thyristor is

(A) 6 s (B) 4 s

(C) 2 s (D) 1 s Q.2 The latching current of a thyristor circuit in

figure is 50 mA. The duration of the firing pulse is 50 s.

Thyristor will fired [Yes/No]

sR20 k20DR

0.1 FC 1SCR

sR

sR

20 k

20 k

20DR

20DR

0.1 FC

0.1 FC

2SCR

3SCR

4 kV

S D

100 A(Volt)

SV

/ 0.02dV dI

0 1VV

(A)S

I

V-I characteristic of IGBT

(a) (b)

(Volt)D

V

/ 0.01dV dI 0 0.7VV

(A)D

I

V-I characteristic of diode

100 V

0.1 mH

20

0.5 H

100 V

1Ti



Latching current for an SCR, inserted in between a dc voltage source of 200 V and the load is 100 mA.

Q.3 The pulse width. If load is 0.2HL is _____ sec

Q.4 The pulse width if load 20R , 0.2HL is

_____ sec

Q.5 The pulse width if load 20R , 2HL is

_____ sec

Q.6 In a thyristor

(A) latching current LI is associated with turn-off

process and holding current HI with turn-on

process.

(B) both LI and HI are associated with turn-off

process.

(C) HI is associated with turn-off process and LI

with turn-on process.

(D) both LI and HI are associated with turn-on

process.

Q.7 The thyristor in figure has a latching current of 50 mA and is fired by a pulse of length 50 s.

The maximum value of R to ensure firing of thyristor is

(A) 2.5k (B) 1.5k

(C) 5k (D) 3.5k

Q.8 An SCR requires 50 mA gate current to switch it ON. The driver circuit supply voltage is 10 V. The gate-cathode drop is about 1 V. The resistive load supplied from a 100 V dc supply is

(A) 66 (B) 73

(C) 80 (D) 100

Q.9 Consider the following statements :

SCR can be turned on by

1. Applying anode voltage at a sufficiently fast rate

2. Applying sufficiently large anode voltage

3. Increasing the temperature of SCR to sufficiently large value

4. Applying sufficiently large gate current

Which of the above statements are correct?

(A) 1, 2 and 3 (B) 1, 3 and 4

(C) 1, 2 and 4 (D) 2, 3 and 4

Q.10 Turn on time of an SCR can be reduced by using a

(A) Rectangular pulse of high amplitude and narrow width

(B) Rectangular pulse of low amplitude and wide width

(C) Triangular pulse

(D) Trapezoidal pulse

Q.11 For the V-I characteristics of an SCR, which of the following statements are correct ?

1. It will trigger when the applied voltage is more than the forward break over voltage

2. Holding current is greater than latching current

3. When reverse biased, a small value of leakage current will flow

4. It can be triggered without gate current

(A) 1, 2 and 3 (B) 1, 3 and 4

(C) 1, 2 and 4 (D) 2, 3 and 4

Q.12 Consider the following statements regarding Thyristor

1. It conducts when forward biased and positive current flows through the gate.

2. It conducts when forward biased and negative current flows through the gate.

3. It commutates when reverse biased and negative current flows through the gate.

4. It commutates when the gate current is withdrawn.

Which of these statements are correct?

(A) 1, 2 and 3 (B) 1 and 2 only

(C) 2 and 3 only (D) 1 only

R100 V

20

0.5 H


Q.13 When a thyristor in the forward blocking state, then

(A) All 3 junctions are reverse biased.

(B) Anode and cathode junctions are forward biased but gate junction is reverse biased.

(C) Anode junction is forward biased but other two are reverse biased.

(D) Anode and gate junctions are forward biased but cathode is reverse biased.

Q.14 In forward-bias portion of the thyristor's i-v characteristic, the number of stable operating regions is

(A) One (B) Two

(C) Three (D) None

Q.15 Circuit turn-off time of an SCR is defined as the time

(A) taken by the SCR to turn off

(B) required for the SCR current to become zero

(C) for which the SCR is reverse biased by the commutation circuit

(D) for which the SCR is reverse biased to reduce its current below the holding current

Q.16 An SCR is in conducting state a reverse voltage is applied between anode and cathode, but it fail to turn off. The reason may be

(A) Positive voltage is applied to the gate.

(B) The reverse voltage is small.

(C) The anode current is more than the holding current.

(D) Turn off time of SCR is large.

Q.17 An SCR is considered to be a semi-controlled device because,

(A) it can be turned OFF but not ON with a gate pulse

(B) it conducts only during one half-cycle of an alternating current wave

(C) it can be turned ON but not OFF with a gate pulse

(D) it can be turned ON only during one half-cycle of an alternating voltage wave

Q.18 The anode current through a conducting SCR is 10 A. If its gate current is made one fourth, then the anode current will be

(A) 0 A (B) 5 A (C) 10 A (D) 20 A Q.19 The junction capacitance of a thyristor is

2 20 pFJC and can be assumed independent of

off-state voltage. The limiting value of charging current to turn on the thyristor is 15 mA. If a capacitor of 0.01 F is connected across the

thyristor, the critical value of dv/dt will be (A) 1.5V / s (B) 2.5V / s

(C) 3.5V / s (D) 4.5V / s Q.20 Figure shows a thyristor with the standard

terminations of abode (A), cathode (K), gate (G) and the different junctions named J1, J2 and J3. When the thyristor is turned ON and conducting.

(A) J1 and J2 are forward biased and J3 is

reversed biased. (B) J1 and J3 are forward biased and J2 is

reverse biased. (C) J1 is forward biased and J2 and J3 are

reverse biased. (D) J1, J2 and J3 are all forward biased. Q.21 The main reason for connecting a pulse

transformer at the output stage of a thyristor triggering circuit is to

(A) amplify the power of the triggering pulse (B) provide electrical isolation (C) reduce he turn on time of the thyristor (D) avoid spurious triggering of the thyristor

due to noise Q.22 The SCR is required to give an average power

dissipation of 0.5 W. Its gate voltage varies from 2.5 V to 10 V. For a triggering gate pulse of duty cycle 0.6, the value of average gate dissipation will be

(A) 0.3 W (B) 0.45 W (C) 0.5 W (D) 0.6 W

PNPN

J3J2J1

K

G

A


Q.23 An SCR has half cycle surge current rating of 3000 A for 50 Hz supply. _____ A is the one cycle surge current rating.

Q.24 To turn off a GTO what is required at the gate?

(A) A high amplitude (but low energy) negative current

(B) A low amplitude negative current

(C) A high amplitude negative voltage

(D) A low amplitude negative voltage

Q.25 Four power semiconductor devices are shown in the figure along with their relevant terminals. The device (s) that can carry dc current continuously in the direction shown when gated appropriately is (are)

(A) Triac only

(B) Triac and MOSFET

(C) Triac and GTO

(D) Thyristor and Triac

Q.26 A thyristor has internal power dissipation of 40 W and is operated at an ambient temperature of 20C if thermal resistance is 16C/W, the junction temperature is

(A) 114C (B) 164 C

(C) 94C (D) 84 C

Q.27 A resistor connected across the gate and cathode of an SCR

(A) Increases dv

dt rating of SCR

(B) Increases holding current of SCR

(C) Decreases noise immunity of SCR

(D) Increases turn-off time of SCR

Q.28 An SCR, during turn on process has the following data :

Anode voltage : 400 V 0 V

Anode current : 0 A 100 A

During turn on time of 8 s, the anode current

and anode voltage varies linearly. If triggering frequency is 100 Hz, the average power loss in thyristor will be

(A) 8.33 W (B) 4.33 W

(C) 6.33 W (D) 5.33 W

Q.29 For an SCR, dv

dt protection is achieved through

the use of

(A) RL in series with SCR

(B) RC across SCR

(C) L in series with SCR

(D) RC in series with SCR

Q.30 In order to get best results per unit cost, the heat sinks on which the thyristors are mounted, are made of

(A) Aluminium (B) Copper

(C) nickel (D) Stainless steel

Q.31 RC snubber is used in parallel with the thyristor to

(A) reduce dv

dt across it

(B) reduce di

dt through it

(C) limit current through the thyristor

(D) ensure its conduction after gate signal is removed

Q.32 A thyristor converter of 415 V, 100 A is operating at rated load. Details of the thyristor used are as follows :

‘ON’ state power loss = 150 W,

Thermal resistance;

Junction to case 00.01 C/W

Case to sink 00.08 C/W

Sink to atmosphere 00.09 C/W

Assume ambient temperature as 035 C . The junction temperature for 100% load is

(A) 048.5 C (B) 054.5 C

(C) 060 C (D) 062 C

Q.33 The thermal resistance between the body of a power semiconductor device and the ambient is expressed as

G

IS

D

G K

I

A

Thyristor

G

I

1MT

2MT

Triac

G K

I

A

GTO MOSFET


(A) Voltage across the device divided by current through the device.

(B) Average power dissipated in the device divided by the square of the rms current in the device.

(C) Average power dissipated in the device divided by the temperature difference from body to ambient.

(D) Temperature difference from body to ambient divided by average power dissipated in the device.

Q.34 The uncontrolled electronic switch employed in power electronic converters is

(A) Thyristor (B) Bipolar junction transistor (C) Diode

(D) MOSFET Q.35 The triac can be used in

(A) Inverter (B) Rectifier

(C) Multi-quadrant chopper (D) AC voltage regulator Q.36 Which semiconductor power device out of the

following is not a current triggered device? (A) Thyristor (B) G.T.O (C) Triac (D) MOSFET Q.37 A triac can be triggered by a gate pulse of -

________ polarity. Q.38 A triac is equivalent to

(A) two diodes in antiparallel (B) one thyristor and one diode in parallel (C) two thyristors in parallel (D) two thyristors in antiparallel Q.39 Match List-I (Characteristics/Action) with List-II

(Observations) and select the correct answer using the codes given below the lists :

List-I (Characteristics/Action) A. Turn-on time of thyristor B. Turn-on time of transistor

C. Rate of rise of gate current in thyristor D. If the gate pulse is removed, when the

thyristor is carrying a current, less than latching current

List-II (Observations)

1. Depends on junction capacitance

2. Is the sum of delay and rise times

3. Thyristor switches back to off-state

4. Affects the delay time

Codes : A B C D

(A) 2 1 4 3

(B) 1 2 3 4

(C) 2 1 3 4

(D) 1 2 4 3

Q.40 A switched mode power supply operating at 20 kHz to 100 kHz range uses as the main switching element,

(A) Thyristor (B) MOSFET

(C) Triac (D) UJT

Conventional Questions :

Q.1 Compute the minimum value of C so that the

SCR is not turn ON due to the applied dv

dt. The

commuting circuit is shown in the figure. The SCR has the capacitance of 20 pF and the minimum charging current to turn ON the SCR is 4 mA.

Q.2.1 Consider the circuit as shown in figure, a DC

source of 100 V supplies a resistive load of 20

a diode is connected in the snubber circuit parameter of 10 . Such that the anode of diode

and thyristor get connected together. The thyristor has just turn ON. Find the minimum value of snubber capacitance, so that the thyristor

will not turn ON due to the firing dv

dt.

The junction capacitance or the capacitance of SCR is 20 pF and the minimum value of charging current to turn ON the thyristor is 4 mA.

100 V

20

CCj


Q.2.2 Calculate the value of sR so that the current

through resistor sR does not exceeds 20 A.

Q.3 A thyristor is placed between a constant dc voltage source of 240 V and resistive load LR .

The specified limits of di

dt and dv

dt for SCR are

60 A/μsec and 300 V/μsec . Determine the value

of inductor and snubber circuit parameter for damping ratio of 0.5.

C

20LR

SV

SRD


Answer Keys

Objective & Numerical Answer Type Questions

1. 100 2. 100.5 3. B 4. 6055-6065

5. 5.996

6. No 7. 9.998 8. 75 9. C 10. C

11. A 12. D 13. D 14. A 15. B

16. D 17. A 18. C 19. D 20. C

21. B 22. 120 23. 10.37 24. 38.56 25. A

26. C 27. D 28. A 29. A 30. B

31. D 32. C 33. B 34. C 35. 0.004

36. A 37. 4 38. 2.6 39. 65 40. C

41. C 42. C 43. C 44. B 45. B

46. C 47. D 48. 170

Practice (Objective & Numerical Answer) Questions

1. B 2. No 3. 100 4. 100.503 5. 1005.03

6. C 7. A 8. * 9. C 10. A

11. B 12. D 13. B 14. B 15. C

16. C 17. C 18. C 19. A 20. B

21. B 22. A 23. 2121.32 24. A 25. B

26. D 27. C 28. B 29. B 30. A

31. A 32. D 33. D 34. C 35. D

36. D 37. +ve, –ve 38. D 39. D 40. B

Conventional Questions

1. 25 nF 2. 25 nF 3. 5 4. 0.16 F

Chapter 2

Single Phase AC to DC Converter


Q.1 In the circuit of adjacent figure the diode

connects the ac source to a pure inductance L.

[GATE 2007, IIT Kanpur]

The diode conducts for

(A) 090 (B) 0180

(C) 0270 (D) 0360

Q.2 The circuit shows an ideal diode connected to a

pure inductor and is connected to a purely

sinusoidal 50 Hz voltage source.

Under ideal conditions the current wave‐form

through the inductor will look like


(A)

(B)

(C)

(D)

Q.3 A single‐phase half wave uncontrolled converter

circuit is shown in figure. A 2‐winding

transformer is used at the input for isolation.

Assuming the load current to be constant and

sinmV V t , the current waveform through

diode 2D will be [GATE 2006, IIT Kharagpur]

(A)

(B)

(C)

D

ACPure

L

0.1HL

50 Hz

D

10sin100 t

0

0.5

10 20 30 40 50

1.5

1

Curr

ent

Time (ms)

0

0.5

10 20 30 40 50

1.5

1

Curr

ent

Time (ms)

0

1

10 20 30 40 50

3

2

Curr

ent

Time (ms)

0

0.5

10 20 30 40 50

1.5

1

Curr

ent

Time (ms)

Li L1D

2DVin

V

0 2

0 2

0 2

GATEACADEMY® 15 SinglePhaseACtoDCConverter

(D)

Q.4 In the circuit shown in the figure, the diode used

is ideal. The input power factor is __________.

(Give the answer up to two‐decimal places.)

[GATE 2017 (Set ‐ 02), IIT Roorkee]

Q.5 A single‐phase, 230 V, 50 Hz ac mains fed step

down transformer (4 : 1) is supplying power to a

half‐wave uncontrolled ac‐dc converter used for

charging a battery (12 V dc) with the series

current limiting resistor being 19.04 . The

charging current is [GATE 2007, IIT Kanpur]

(A) 3.43 A (B) 1.65 A

(C) 1.22 A (D) 1.0 A

:: Common Data Questions 6 to 9 ::

A diode whose internal resistance is 20 is to

supply power to a 1000 load from a 230 V

(rms) source of supply. [IAS : 1983]

Q.6 The peak load current is ________ A

Q.7 The dc load current is ________ A

Q.8 The dc diode voltage is ________ V

Q.9 The percentage regulation from no load to given

load is __________ %

Q.10 Consider a phase‐controlled converter shown in

the figure. The thyristor is fired at an angle in every positive half cycle of the input voltage. If

the peak value of the instantaneous output

voltage equals 230 V, the firing angle is close to [GATE 2005, IIT Bombay]

(A) 045 (B) 0135

(C) 090 (D) 083.6

Q.11 A half‐wave thyristor converter supplies a

purely inductive load, as shown in figure. If the

triggering angle of the thyristor is 0120 , the

extinction angle will be


(A) 0240 (B) 0180

(C) 0200 (D) 0120

Q.12 A diode circuit feeds an ideal inductor as shown

in the figure. Given 100sin( )V,sV t where

100 rad/s and 31.83mH.L The initial value

of inductor current is zero. Switch S is closed at

2.5ms.t The peak value of inductor current Li

(in A) in the first cycle is___________.

[GATE 2014, IIT Kharagpur]

Q.13 In the circuit shown in figure, L is large and the

average value of ‘i’ is 100 A. The thyristor is

gated in the ______ half cycle of ‘e’ at a delay

angle is equal to _____. ( ) 200 2 sin314 Ve t t


Q.14 The figure shows the circuit diagram of a

rectifier. The load consists of a resistance 10

0 2

10 100sin(100 ) Vt

0vR230 (RMS)50 Hz

Lsinm

V t

sV

Li

L

2.5 mst

S

( )e t

0.01R

E

i

20 V

L

PowerElectronics[Workbook] 16 GATEACADEMY®

and an inductance 0.05 H connected in series.

Assuming ideal thyristor and ideal diode, the

thyristor firing angle (in degree) needed to

obtain an average load voltage of 70 V is

_______. [GATE 2014 (Set ‐ 01), IIT Kharagpur]

Q.15 In the single phase diode bridge rectifier shown

in below figure, the load resister is 50R .

The source voltage is 200sin( )v t , where

2 50 radians per second. The power

dissipate in the load resistor R is

[GATE 2002, IISc‐Bangalore]

(A) 3200

W

(B) 400

W

(C) 400 W (D) 800 W

Q.16 The circuit in figure shows a full‐wave rectifier.

The input voltage is 230 V (rms) single‐phase ac.

The peak reverse voltage across the diodes 1D

and 2D is [GATE 2004, IIT‐Delhi, ESE 2009]

(A) 100 2 V (B) 100 V

(C) 50 2 V (D) 50 V


A single‐phase full bridge diode rectifier is

supplied from 230 V, 50 Hz source. The load

consists of 10R and a large inductance so as

to render the load current constant.

Q.17 The average value of output voltage is ______ V

Q.18 The average value of output current is ______ A

Q.19 The average value of diode currents is ______ A

Q.20 The rms value of diode current is __________ A

Q.21 The rms value of output current is _______ A

Q.22 The rms value of source current is _________ A

Q.23 The supply power factor is ________ lag

Q.24 The fully controlled thyristor converter in the

figure is fed from a single‐phase source. When

the firing angle is 00 , the dc output voltage of

the converter is 300 V. The output voltage for a

firing angle of 060 will be, assuming continuous

conduction is [GATE 2010, IIT Guwahati]

(A) 150 V (B) 210 V

(C) 300 V (D) 100 V

Q.25 A fully controlled converter bridge feeds a

highly inductive load with ripple free load

current. The input supply ( )s

v to the bridge is a

sinusoidal source. Triggering angle of the bridge

converter is 030 . The input power factor of

the bridge is _________.

[GATE 2014, IIT‐Kharagpur]

325sin(314 ) Vt

Load

R

1D

230 V50 Hz

2D

230 V/50-0-50 V

0v

si

Load

sV


Q.26 A single phase fully controlled converter bridge

is used for electrical breaking of a separately

excited dc motor. The dc motor load is

respectively by an equivalent circuit as shown in

the figure.

Assume that the load inductance is sufficient to

ensure continuous and ripple free load current.

The firing angle of the bridge for a load current

of 0 10 AI will be


(A) 044 (B) 051

(C) 0129 (D) 0136

Q.27 A full‐bridge converter supplying an RLE load

is shown in figure. The firing angle of the bridge

converter is 1200. The supply voltage

( ) 200 sin(100 ) Vmv t t , R = 20 Ω, E = 800 V. The

inductor L is large enough to make the output

current LI a smooth dc current. Switches are

lossless. The real power feedback to the source,

in kW, is ________.

[GATE 2016 (Set‐2), IISc‐Bangalore]

:: Common Data Question 28 & 29 ::

The input voltage given to a converter is

100 2 sin 100 Viv t

The current drawn by the converter is

10 2 sin 100 / 3 5 2 sinii t

300 / 4 2 2 sin 500 / 6 At t


Q.28 The input power factor of the converter is

(A) 0.31 (B) 0.44

(C) 0.5 (D) 0.71

Q.29 The active power drawn by the converter is

(A) 181 W (B) 500 W

(C) 707 W (D) 887 W

Q.30 The figure shows the circuit of a rectifier fed

from a 230 V (rms), 50 Hz sinusoidal voltage

source. If we want to replace the current source

with a resistor so that the rms value of the

current supplied by the voltage source remains

unchanged, the value of the resistance (in ohms)

is _________(Assume diodes to be ideal).


Q.31 A single‐phase bridge converter is used to

charge a battery of 200 V having an internal

resistance of 2 as shown in figure. The SCRs

are triggered by a constant dc signal. If 2SCR

gets open circuited, then the average charging

current will be


(A) 23.8 A (B) 15 A

(C) 11.9 A (D) 3.54 A

0i

230 V,50 Hz

2

150 V

L

20R

800 VE

1T 3T

2T4T

mv

LI Load

Bridge

230 V, 50 Hz

10 A

230 V50 Hz

1SCR 2SCR

3SCR 4SCR

200 VBattery


Q.32 The figure below shows the circuit diagram of a

controlled rectifier supplied from a 230 V, 50 Hz,

1‐phase voltage source and a 10 : 1 ideal

transformer. Assume that all devices are ideal.

The firing angles of the thyristors 1T and 2T are 090 and 0270 respectively

The RMS value of the current through diode 3D

in amperes is _______


Q.33 The waveform of the current drawn by a semi‐

converter from a sinusoidal AC voltage source is

shown in the figure. If 0 20 AI , the rms value

of fundamental component of the current is

______ A (up to 2 decimal places).

[GATE 2018, IIT Guwahati]

Q.34 In the given rectifier, the delay angle of the

thyristor 1T measured from the positive going

zero crossing of sV is 030 . If the input voltage

sV is 100sin (100 )V,t the average voltage

across R (in Volt) under steady‐state is _______.

[GATE 2015 (Set ‐ 02), IIT Kanpur]

Q.35 A single phase fully controlled rectifier is

supplying a load with an anti‐parallel diode as

shown in the figure. All switches and diodes are

ideal. Which one of the following is true for

instantaneous load voltage and current?


(A) 0 0v and 0 0i (B) 0 0v and 0 0i

(C) 0 0v and 0 0i (D) 0 0v and 0 0i

Q.36 A phase controlled single phase rectifier,

supplied by an AC source, feeds power to an R‐

L‐E load as shown in the figure. The rectifier

output voltage has an average value given

0 (3 cos )2

mVV

, where 80mV volts and

is the firing angle. If the power delivered to the

lossless battery is 1600 W, in degree is

__________ (up to 2 decimal places).


Q.37 The figure below shows an uncontrolled diode

bridge rectifier supplied from a 220 V, 50 Hz, 1‐

phase ac source. The load draws a constant

current 0 14 AI . The conduction angle of the

diode 1D , in degrees (rounded off to two

decimal places) is ________.


230 V,50 Hz

10 :1

1T 2T

1D 2D

3D R

3Di

300

I0

2100

I0

sin( )m

V t

t

Voltage and

current

1T

4D 2D

3D

sV

R 0v

+

–

v0

i0

Load

sin( )m

V t

80 VBattery

10 mH

2

0V


Q.38 A single phase fully controlled thyristor bridge

ac‐dc converter is operating at a firing angle of

25 and an overlap angle 10 with constant dc

output current of 20 A. The fundamental power

factor at input ac mains is


(A) 0.78 (B) 0.827

(C) 0.866 (D) 0.9


Q.1 A 1‐phase half wave converter has 120 V, 60 Hz

input voltage with 10R . Average output

voltage is 25% of maximum possible output

voltage. The delay angle in degree of converter

is ______.

Q.2 If 1- H.W. controlled rectifier is fired at an

angle of 090 , then ripple factor of the output

rectified wave will be

(A) 2

2

(B)

2 2

2

(C) 2 1

2

(D)

2 3

2

Q.3 A 1‐phase full bridge diode rectifier delivers a

constant load current of 20 A. Average and rms

values of source current respectively are

(A) 20 A, 20 A (B) 10 A, 10 A

(C) 10 A, 20 A (D) 0 A, 20 A

Q.4 A single phase diode bridge rectifier supplies a

highly inductive load. The load current can be

assumed to be ripple free. The ac supply side

current waveforms will be

(A) Sinusoidal (B) Constant dc

(C) Square (D) Triangular


A single phase one pulse converter with RLE

load has the following parameters : supply

voltage : 230 V at 50 Hz, load : R 2 , L = 1

mH, E = 120 V. Extinction angle 0220 , firing

angle 025

Q.5 The voltage across thyristor at the instant SCR is

triggered is_________.

(A) 7.46 V (B) 17.46 V

(C) 8.46 V (D) 18.46 V

Q.6 The voltage that appears across SCR when

current decays to zero is________.

(A) 129 V (B) 229 V

(C) 329 V (D) 429 V

Q.7 The PIV of the SCR is________.

(A) 445.3 V (B) 545.3 V

(C) 645.3 V (D) 745.3 V

:: Common Data Questions 8 & 9 ::

A half‐wave controlled rectifier circuit is

connected to a purely resistive load. When 0

min 10 . The latching and holding current for

thyristor are 10 mA and 5 mA respectively. The

circuit is operated from 100sin 314v t .

Q.8 The maximum value of the resistance to be

connected as a load is ____________

Q.9 The angle of conduction of thyristor is

___________ degree


A single‐phase full converter, connected to

230 V , 50 Hz source, is feeding a load 10R

in series with a large inductance that makes the

load current ripple free. For a firing angle of 045

Q.10 The average output voltage is ______ V

Q.11 The average output current is ______ A

Q.12 The RMS output voltage is ______ V

Q.13 The RMS output current is ______ A

Q.14 The DC output power is ______ Watt

Q.15 The AC output power is ______ Watt

Q.16 The rectification efficiency is ______%

Q.17 The voltage ripple factor is ______

Ls= 10 mH

220 V,50 Hz

D1

D4

D3

D2

I0 = 14 A


Q.18 The current ripple factor is ______

Q.19 The fundamental RMS source current is_____ A

Q.20 The displacement angle is ______ degree

Q.21 The displacement factor is _______

Q.22 The current distortion factor is _______

Q.23 The total harmonic distortion is _______

Q.24 The active power input is _______ Watt

Q.25 The reactive power input is _______ VAr

Q.26 The input power factor is ______


A dc battery of constant emf E is being charged

through a resistor as shown in figure. For source

voltage of 230 V, 50 Hz and for 8R ,

150VE

Q.27 The value of average charging current is ____A

Q.28 The power supplied to battery is _________W

Q.29 The power that dissipated in the resistor is __ W

Q.30 The supply power factor is _____________

Q.31 The charging time is ___________ hour in case

battery capacity is 1000 Wh,

Q.32 The rectifier efficiency is __________ %

Q.33 PIV of the diode is _______________ V.

Q.34 A single phase full converter bridge is connected

to R‐L‐E load. The source voltage is 230 V 50 Hz.

The average load current of 10 A is continuous

over the working range. For R 0.4 L = 2 mH,

the firing angle corresponding to power flow for

E = – 120 V is

(A) 53.21 and power flow from ac source to dc

load.

(B) 53.21 and power flow from dc load to as

source.

(C) 124.1 & power flow from dc load to ac

source.

(D) 124.1 & power flow from ac source to dc

load.

Q.35 A single‐phase mid point SCR converter

supplies constant load current of 5 amps when

the triggering angle is maintained at 035 . The

input voltage to the converter is 220 V, 50 Hz.

The turns ratio from primary to each secondary

is 1/2. The load voltage in volts is ________.


In a single phase mid point converter, turns

ratio from primary to each secondary is 1.25.

The source voltage is 230 V, 50 Hz. For a

resistive load of R 2 .

Q.36 The Maximum value of average output voltage

and load current are respectively

(A) 265.63 V, 42.83 A (B) 265.63 V, 82.83 A

(C) 165.63 V, 42.83 A (D) 165.63 V, 82.83 A

Q.37 The corresponding firing and conduction angles

are respectively:

(A) 00 , 090 (B) 090 , 0180

(C) 00 , 0180 (D)

0180 , 00

Q.38 Maximum permissible value of negative voltage

across SCR’s is

(A) 520.4 V (B) 420.4 V

(C) 320.4 V (D) 220.4 V

Q.39 Maximum average thyristor current is

(A) 41.41 A (B) 51.51 A

(C) 61.61 A (D) 71.71 A

Q.40 The value of for average load voltage of 100 V

is

(A) 052 (B) 068

(C) 078 (D) 088


A single‐phase full converter bridge is

connected to RLE load. The source voltage is 230

V, 50 Hz. The average load current of 10 A is

constant over the working range. For 0.4R

and 2mHL ,

Q.41 The firing angle delay for 120VE is

___________ degree

Q.42 The input power factor for 120VE is

__________.

0v

++

+

+

sins m

v V t

Dv

S

RRv

E

0i


Q.43 The firing angle delay for 120VE is

__________ degree

Q.44 The input power factor for 120VE is

__________.


A single‐phase full converter feeds power to

RLE load with 6R , 6mHL and 60VE .

The ac source voltage is 230 V, 50 Hz. For

continuous conduction,

Q.45 The average value of load current for a firing

angle delay of 050 is ____________ A

Q.46 In case one of the four SCRs gets open circuited

due to a fault the new value of average load

current taking the output current as continuous

is _________ A

Q.47 A half‐controlled single‐phase bridge rectifier is

supplying an R‐L load. It is operated at a firing

angle and the load current is continuous. The

fraction of cycle that the freewheeling diode

conducts is

(A) 1

2 (B)

1

(C) 2

(D)


A single – phase semi converter delivers power

to RLE load with R 5 , L = 10 mH and E = 80

V. The ac source voltage is 230 V, 50 Hz.

Q.48 For a continuous conduction, find the average

value of output current for a firing angle delay

of 050 .

(A) 18 A (B) 28 A

(C) 38 A (D) 48 A

Q.49 If main SCR 2T is damaged and open circuited,

find the new value of average output current on

the assumption of continuous conduction.

(A) 4 A (B) 3 A

(C) 2 A (D) 1 A


A single phase bridge full converter is connected

to an ac supply of 330sin314t . It operates at

/ 4 . The load current is maintained at 5

Amp and load voltage is 140 Volts.

Q.50 The value of load resistance is

(A) 7 (B) 14

(C) 21 (D) 28

Q.51 The value of source inductance is

(A) 17.1 mH (B) 18.1 mH

(C) 19.1 mH (D) 20.1 mH

Q.52 The value of overlap angle is

(A) 05.26 (B) 06.26

(C) 07.26 (D) 08.26


A single‐phase full‐converter is supplied from

230 V, 50 Hz source. The load consists of

10R and a large inductance so as to render

the load current constant. For a firing angle

delay of 030 . If source has an inductance of 1.5

mH,

Q.53 The average output voltage is __________V

Q.54 The angle of overlap is __________ degree

Q.55 The input power factor is _______ .

Q.56 A single phase dual converter operated from 230

V, 50 Hz supply and the load resistance is 20 W ,

the circulating inductance is 25mHcL , delay

angle area 01 60 and 0

2 120 . The value of

peak circulating current and the peak current of

converter are respectively

(A) 41.41 A, 57.67 A (B) 51.51 A, 57.67 A

(C) 41.41 A, 77.77 A (D) 11.11 A, 77.77 A


A full‐wave rectifier connected to secondary of

transformer (primary 230 V, secondary 40‐0‐40

V) and the output is used to charge a battery of

12 V Current limiting resistance is put in series

with the battery.

Q.57 The conduction angle of each diode is ________

degree

Q.58 The value of limiting resistance if 4AdcI is

__________

Q.59 The power rating of the current limiting

resistance is ________ W

Q.60 The rectifier efficiency is _________ %


Q.61 A single‐phase full‐bridge diode rectifier

delivers a constant load current of 10 A, Average

and RMS values of source current, are

respectively

(A) 5 A, 10 A (B) 10 A, 10 A

(C) 5 A, 5 A (D) 0 A, 10 A

Q.62 The lowest frequency of ac components in the

outputs of half‐wave and full‐wave rectifiers

are, respectively, (where is the input

frequency)

(A) 0.5 and (B) and 2

(C) 2 and (D) and 3

Q.63 A 1- H.W. controlled rectifier with RLE load

has firing angle and extinction angle 030 and 0210 respectively. The source frequency is 2.5

kHz. The circuit turn‐off time is ______________

Sec


A resistive load of 10 is connected through a

half wave circuit to 220 V, 50 Hz single phase

source.

Q.64 The power delivered to load for a firing angle of 060 is.

(A) 1946 W (B) 935 W

(C) 2935 W (D) 293 W

Q.65 The value of input power factor is

(A) 0.334 lag (B) 0.434 lag

(C) 0.534 lag (D) 0.634 lag


A 230 V, 50 Hz, one‐pulse SCR controlled

converter is triggered at a firing angle of 040

and the load current extinguishes at an angle of 0210 . For load parameters 5R , 2mHL

and 110VE

Q.66 The circuit turn off time is ______________ m‐sec

Q.67 The average output voltage is __________ V

Q.68 The average load current is _______________ A


A single‐phase transformer, with secondary

voltage of 230 V, 50 Hz, delivers power to load

10R through a half‐wave controlled rectifier

circuit. For a firing‐angle delay of 060 .

Q.69 The rms value of output voltage is _____ V.

Q.70 The rectification efficiency is __________ %

Q.71 The form factor is _________

Q.72 The transformer utilization factor is __________

Q.73 The PIV of thyristor is ___________ V

Q.74 When the firing angle of a single phase, fully controlled rectifier feeding constant dc current

into a load is 030 , the displacement power factor

of the rectifier is

(A) 1 (B) 0.5

(C) 1

3 (D)

3

2

Q.75 A single‐phase full‐bridge converter with a free‐

wheeling diode feeds an inductive load. The

load resistance is 15.53 and it has a large

inductance providing constant and ripple free

d.c. current. Input to converter is from an ideal

230 V, 50 Hz single phase source. For a firing

delay angle of 060 , the average value of diode

current is

(A) 10 A (B) 8.165 A

(C) 5.774 A (D) 3.33 A

Q.76 If the r.m.s. source voltage is V volts, the

minimum and maximum value of firing angles

for a single‐phase, half‐wave controlled rectifier,

supplying a load with a back e.m.f. of 40 volts

are

(A) 0 00 and 180

(B) -1 040α sin and 180

V 2

(C) -1 140 40α sin and sin

V 2 V 2

(D) 0 1 400 and sin

V 2

Q.77 A fully controlled line commutated converter

functions as an inverter when firing angle

( ) is in the range

(A) 0 00 -90

(B) 0 090 180-

(C) 0 090 -180 only when there is a suitable d.c.

source in the load

(D) 0 090 -180 only when it supplies a back e.m.f.

load


Q.78 In a single phase full wave controlled bridge

rectifier, minimum output voltage and

maximum output voltage are obtained at which

conduction angles ?

(A) 0 00 ,180 respectively

(B) 0 0180 ,0 respectively

(C) 0 00 , 0 respectively

(D) 0 0180 ,180 respectively

Q.79 A single‐phase full‐wave controlled bridge

converter supplies a load drawing constant and

ripple free load current. If the triggering angle is 030 , the input power factor will be

(A) 0.65 (B) 0.78

(C) 0.85 (D) 0.866

Q.80 Statement (I): The main function of a

freewheeling diode in Rectifier circuits is to

prevent the reversal of load voltage.

Statement (II): The freewheeling diode is never

connected across the load.

(A) Statement (I) and Statement (II) are

individually true and Statement (II) is the

correct explanation of Statement (I)

(B) Statement (I) and Statement (II) are

individually true but Statement (II) is not

the correct explanation of Statement (I)

(C) Statement (I) is true but Statement (II) is

false

(D) Statement (I) is false but Statement (II) is

true

Q.81 A freewheeling diode in phase‐controlled

rectifiers

(A) enables inverter operation

(B) is responsible for additional reactive power

(C) improves the line power factor

(D) is responsible for additional harmonics

Q.82 A single phase full converter feeding an RLE

load is fed by 230 volts, 50 Hz mains. If R = 5

ohms, L = 8 mH and E = 50 volts, assuming that

conduction is continuous and firing angle is 040 ,

the average value of load current in ampere

is___________.

Q.83 A single phase full converter supplies power to

RLE load. The source voltage is 230 V, 50 Hz

and for load R 2 , L = 10 mH, E = 100 V, for a

firing angle of 030 , find the average value of

output current and output voltage in case the

load current extinguishes at 0200 ?

(A) 36.25A,192.5V (B) 46.25A,92.5 V

(C) 36.25A,92.5V (D) 46.25A,192.5V

Q.84 In a single‐phase full converter, if output voltage

has peak and average values of 325 V and 133 V

respectively, then the firing angle is

(A) 040 (B) 0140

(C) 050 (D) 0130 Q.85 In phase‐controlled converters feeding RL load,

the ripple content of load current is decided by

(A) load resistance alone

(B) load inductance alone

(C) both R and L

(D) neither R nor L

Q.86 On increasing the number of pulses in

rectification the form factor, ripple frequency

and efficiency

(A) all increase.

(B) decrease, decrease and increase respectively.

(C) decrease, increase and increase respectively.

(D) increase, decrease and increase respectively.

Q.87 A transformer is having source voltage 400 volts

and turns ratio 2:1. The transformer is centre‐

tapped. If secondary is connected to 1- F.W.

converter. PIV per SCR is

(A) 200 2 (B) 100 2

(C) 200 (D) 100

Q.88 The output of a single‐phase full‐wave rectifier

contains

(A) dc plus even harmonics

(B) dc plus odd harmonics

(C) dc plus both odd and even harmonics

(D) dc and no harmonics

:: Common Data Questions 89 to 93::

A single‐phase full‐converter is supplied from

230 V, 50 Hz source. The load consists of

10R and a large inductance so as to render

the load current constant. For a firing angle

delay of 030 :


Q.89 The average output voltage is __________ V

Q.90 The average output current is ________ A

Q.91 The average value of thyristor current is _____ A

Q.92 The rms values of thyristor current is _______ A

Q.93 The power factor is _________

Q.94 Match List‐I ( Rectifier topology‐feeding

resistive load) with List‐II (Average output

voltage) and select the correct answer using the

codes given below the lists ( is the firing angle)

List‐I [ESE 2001]

( Rectifier topology‐feeding resistive load)

A. Uncontrolled – half wave

B. Controlled – half wave

C. Controlled – full wave

D. Semi‐controlled full wave

List‐II

(Average output voltage)

1. V

(1 cos )peak

2. 2V

cospeak

3. Vpeak

4. V

(1 cos )2peak

Codes : A B C D

(A) 3 2 4 1

(B) 1 4 2 3

(C) 3 4 2 1

(D) 1 2 4 3

Q.95 A half‐controlled single‐phase converter is

shown in below figure. The control angle 030

The output dc voltage wave shape will be as

shown in

(A)

(B)

(C)

(D)


A single‐phase semiconverter, connected to

230 V 50 Hz source, is feeding a load 10R in

series with a large inductance that makes the

load current ripple free. For a firing angle of 045

Q.96 The average output voltage is ______ V

Q.97 The average output current is ______ A

Q.98 The RMS output voltage is ______ V

Q.99 The RMS output current is ______A

Q.100 The DC output power is ______ Watt

Q.101 The AC output power is ______ Watt

Q.102 The rectification efficiency is ______%

Q.103 The voltage ripple factor is ______

Q.104 The current ripple factor is ______

Q.105 The fundamental RMS source current is _____ A

Q.106 The RMS source current is ______A

Q.107 The displacement angle is ______ degree

Q.108 The displacement factor is _______

Q.109 The current distortion factor is _______

Q.110 The total harmonic distortion is _______

DCI

acV

DCV

1T 2T

2D 1D

dcV

t 2

dcV

2 t

2

dcV

t

dcV

t 2


Q.111 The active power input is _______ Watt

Q.112 The reactive power input is _______ VAr

Q.113 The input power factor is _______

Q.114 A single phase half wave controlled rectifier has

400sin 314t as the input voltage and R as the

load. For the firing angle of 060 for the SCR the

average output voltage is

(A) 400

(B)

300

(C) 240

(D)

200


The single phase half controlled ac to dc bridge

converter feeds a 10 resistor in series with a

100 V back emf load. The firing angle of the

thyristors is set to 060 . Consider a supply

voltage of 200 V.

Q.115 The average current through the resistor is____.

(A) 6.4 A (B) 7.4 A

(C) 8.4 A (D) 5.4 A

Q.116 What will be the new average current through

the resistor, if a very large inductor is connected

in series with the load?

(A) 0.5 A (B) 1.5 A

(C) 2.5 A (D) 3.5 A


A single‐phase semiconverter, using two

thyristors and two diodes (symmetrical

configuration) is supplied from 230 V, 50 Hz

source. The load consists of 10R , 100VE

and a large inductance so as to render the load

current level. For a firing delay angle of 030

Q.117 The average output voltage is _____________ V

Q.118 The average output current is ____________ A

Q.119 The average value of thyristor current is ____ A

Q.120 The rms value of thyristor current is ________ A

Q.121 The average value of diode current is _______ A

Q.122 The rms value of diode current is ___________ A

Q.123 The rms value of source current is __________ A

Q.124 The input power factor is ___________

Q.125 The circuit turn‐off time is __________ m‐sec


A single‐phase asymmetrical semiconverter

feeds an RL load with 10R and a large L so

that load current is level. The source voltage is

230 V, 50 Hz. For firing angle delay of 030

Q.126 The average value of output voltage is ______ V

Q.127 The average value of output current is ______ A

Q.128 The average value of thyristor current is _____ A

Q.129 The rms value of thyristor current is ________ A

Q.130 The average value of diode current is ________A

Q.131 The rms value of diode current is ___________ A

Q.132 The rms value of source current is __________ A

Q.133 The input power factor is ___________

Q.134 The circuit turn‐off time is __________ m‐sec.

Q.135 In the circuit shown, the diodes are ideal, the

inductance is small and 0 0I . Which one of the

following statement is true?

(A) 1D conducts for greater than 0180 , 2D

conducts for greater than 0180

(B) 2D conducts for more than 0180 , 1D

conducts for 0180

(C) 1D conducts for 0180 , 2D conducts for 0180

(D) 1D conducts for more than 0180 , 2D

conducts for 0180

Q.136 A single phase full converter is supplied from

230 V, 50 Hz supply. The load current is

continuous and ripple free. If the average

current 0 150 AmpI and the source inductance

0.1mHsL . The overlap angle at 010 is

(A) 01.95 (B) 02.95

(C) 03.95 (D) 04.95

Q.137 If the commutation angle of a diode rectifier

(due to source inductance) is , then inductive

voltage regulation is

D2 I0

D1


(A) 1 cos

2

(B)

cos1

2

(C) cos

12

(D)

1 cos

2


230 V, 50 Hz supply. The load current is

continuous and ripple free. If the average load

current is 150 Amp and source inductance

0.2 mHsL . The overlap angle at 030 is

(A) 01.17 (B) 02.17

(C) 03.17 (D) 04.17

Q.139 A single phase fully controlled bridge rectifier

feeds load of 10 Amp. constant current from 230

V, 50 Hz AC input. If source inductance present

is 2.5 mH per phase, the overlap angle (in

degree) for firing angle of 030 is ________.

Q.140 Consider the following statement

The overlap angle of a phase controlled

converter would increase on increasing.

1. Supply voltage 2. Supply frequency

3. Load current 4. Source inductance

Of these statements

(A) 1, 2 & 3 are correct

(B) 1, 2, 3 & 4 are correct

(C) 1, 2 & 4 are correct

(D) 2, 3 & 4 are correct

Q.141 Consider the following statements :

The overlap angle of a phase‐controlled

converter will increase

1. as the firing angle increases.

2. as the frequency of supply increases.

3. as the supply voltage decreases.

Of these statements,

(A) 1, 2 and 3 are correct

(B) 2 and 3 are correct

(C) 1 and 3 are correct

(D) 1 and 2 are correct

Q.142 Overlap in a phase‐controlled converter, under

continuous conduction, does not depend on

(A) frequency (B) applied voltage

(C) load current (D) load inductance

Q.143 In a single‐phase full converter, the number of

SCRs conducing during overlap is

(A) 1 (B) 2

(C) 3 (D) 4


230 V 50 Hz source. The load consists of

R 10 and a large inductance so as to render

the load current constant. The source inductance

is 1.5 mH. If the firing angle is 030 , then the

average output voltage is:

(A) 179.4 V (B) 126.78 V

(C) 124.88 V (D) 176.8 V

Q.145 For a 1 full converter with large inductive

load, if the source inductance sL is considered,

the reduction in the output voltage in volt due

to overlap 030 and 02 with supply

voltage of 230 Volts is ____________.

Q.146 A single phase full converter operated from 230

V, 50 Hz gives an output voltage of 180 volts.

When loaded with a constant output current

(continuous and ripple free) of 10 amp, the

overlap angle was found to be 06 . The source

inductance is ____mH


In a single phase full converter the reduction in

the output voltage due to the effect of source

inductance is 3 volts. The load current 0I is

continuous and ripple free equal to 100 Amp. If

supply voltage is 230 V 50 Hz, and / 6 .

Q.147 The value of source inductance in mH is

_______.

Q.148 The value of overlap angle in degree is

_________.

Q.149 In a dual converter, the circulating current

(A) allows smooth reversal of load current, but

increases the response time.

(B) does not allow smooth reversal of load

current, but reduces the response time.

(C) allows smooth reversal of load current with

improved speed of response.

(D) flows only if there is not interconnecting

inductor


Q.150 A single phase dual converter is operated from a

230 V, 50 Hz supply and delivers a ripple free

current 20AdcI . The circulating inductance

5mHrL and delay angles are 01 30 and

02 150 . The peak current of the converter is

______A.

Q.151 A single SCR is inserted in between voltage

source 200 sin 314 t and a load 10R . If the

gate trigger voltage lags the ac supply voltage

by 0120 , then average load current is

(A) 15

A

(B) 15

A

(C) 5

A

(D) 5

A

Answer Keys


1. D 2. C 3. C 4. 0.707 5. D

6. 0.3189 7. 0.10151 8. – 101.5 9. 1.961 10. B

11. A 12. 17.07 13. +ve, 1220 14. 69 – 70 15. C

16. A 17. 207.04 18. 20.70 19. 10.352 20. 14.642

21. 20.704 22. 20.704 23. 0.90 24. A 25. 0.78

26. C 27. 6 28. B 29. B 30. 23

31. C 32. 0 33. 17.39 34. 61.53 35. C

36. 90 37. 210.86 38. C


1. 120 2. B 3. D 4. C 5. B

6. C 7. A 8. 1736.5 9. 165 10. 146.423

11. 14.6423 12. 230 13. 14.6423 14. 2143.97 15. 3367.73

16. 63.66 17. 1.2114 18. 0 19. 13.183 20. – 45

21. 0.707 22. 0.90032 23. 0.48342 24. 2143.97 25. 2143.97

26. 0.63653 27. 4.96 28. 745 29. 691 30. 0.672

31. 1.34 32. 51.87 33. 475.22 34. C 35. 324.45

36. D 37. C 38. A 39. A 40. A

41. 53.21 42. 124.1 43. 0.5391 44. 0.5043 45. 12.181

46. 1.09 47. D 48. A 49. D 50. D


51. A 52. B 53. 176.614 54. 2.855 55. 0.7679

56. A 57. 155.5 58. 3.10 59. 141.24 60. 25.36

61. B 62. B 63. 1/5000 64. A 65. D

66. 9.432 67. 6.506 68. 9.432 69. 145.87 70. 28.33

71. 1.879 72. 0.179 73. 325.22 74. D 75. A

76. C 77. C 78. B 79. B 80. C

81. C 82. 21 – 22 83. D 84. C 85. C

86. C 87. A 88. A 89. 179.3 90. 17.93

91. 8.965 92. 12.68 93. 0.7796 94. C 95. B

96. 176.72 97. 17.672 98. 219.2 99. 17.672 100. 3122.996

101. 3878.996 102. 80.85 103. 0.735 104. 0 105. 17.697

106. 15.304 107. – 22.5 108. 0.9239 109. 0.9603 110. 0.2905

111. 3122.996 112. 1392.79 113. 0.8872 114. B 115. B

116. D 117. 193.1722 118. 9.32 119. 4.66 120. 6.56

121. 4.66 122. 6.59 123. 8.508 124. 0.92 125. 8.33

126. 193.172 127. 19.32 128. 8.05 129. 12.47 130. 11.27

131. 14.756 132. 17.64 133. 0.92 134. 10 135. A

136. C 137. D 138. C 139. 2.66 140. D

141. B 142. D 143. D 144. D 145. 2

146. 5.31 147. 0.3 148. 3.0 – 3.2 149. C 150. 47.23

151. D

Chapter 3

Three Phase AC to DC Converter


Q.1 The circuit in figure shows a 3‐phase half‐wave

rectifier. The source is a symmetrical, 3‐phase

four‐wire system. The line‐to‐line voltage of the

source is 100 V. The supply frequency is 400 Hz.

The ripple frequency at the output is


(A) 400 Hz (B) 800 Hz

(C) 1200 Hz (D) 2400 Hz

Q.2 In a 3‐phase half‐wave diode rectifier, the ratio

of average output voltage to per‐phase

maximum ac voltage is

(A) 0.955 (B) 0.827

(C) 1.654 (D) 1.169

Q.3 In a 3‐phase half‐wave rectifier, dc output

voltage is 230 V. The peak inverse voltage across

each diode is

(A) 481.7 V (B) 460 V

(C) 345 V (D) 230 V

Common Data Question for 4 to 7::

A 3‐phase half‐wave controlled converter is fed

from 3‐phase, 400 V, 50 Hz source and is

connected to load taking a constant current of 36

A. Thyristors have a voltage drop of 1.4 V.

Q.4 The average output voltage for 030 is_____

V.

Q.5 The rms current rating of thyristor is_____ A.

Q.6 The PIV rating of thyristor is _____ V.

Q.7 The average power dissipation in each thyristor

is __________ W.

Common Data Questions 8 to 13 ::

Consider B‐6 converter shown in below figure.

Assume continuous conduction ripple free load

current due to large value of inductance.

Q.8 The average value of diode current (in Amp) is

_______.

Q.9 The RMS value of diode current (in Amp) is

_______.

Q.10 The average value of thyristor current (in Amp)

is _______.

Q.11 The RMS value of thyristor current (in Amp) is

_______.

Q.12 The average value of source current (in Amp) is

_______.

Q.13 The RMS value of source current (in Amp) is

_______.


Consider B‐6 converter shown in below figure.

Assume continuous conduction ripple free load

current due to large value of inductance.

R

Y

B

N

1T

6T

2T

5T

0403T

4T

D

0I

a

L

100 VE

b

c

400

V, 5

0 H

z

5R

1T

6T

2T

5T

0100

3T

4T

D

0I

a

L

100 VE

b

c

400

V, 5

0 H

z

5R


Q.14 The average value of diode current (in Amp) is

_______.

Q.15 The RMS value of diode current (in Amp) is

_______.

Q.16 The average value of thyristor current (in Amp)

is _______.

Q.17 The RMS value of thyristor current (in Amp) is

_______.

Q.18 The average value of source current (in Amp) is

_______.

Q.19 The RMS value of source current (in Amp) is

_______.

Q.20 A 3‐phase, fully controlled, converter is feeding

power into a dc load at a constant current of 150

A. The rms current through each thyristor of the

converter is [GATE 1998, IIT Delhi]

(A) 50 A (B) 100 A

(C) 150 2

A3

(D) 150

3

Q.21 A three‐phase, fully controlled thyristor bridge

converter is used as line commutated inverter to

feed 50 kW power at 420 V dc to a three – phase,

415 V (line), 50 Hz ac mains. Consider dc link

current to be constant. The rms current of the

thyristor is [GATE 2007, IIT‐Kanpur]

(A) 119.05 A (B) 79.37 A

(C) 68.73 A (D) 39.68 A

Q.22 A three‐phase diode bridge rectifier is fed from

a 400 V RMS, 50 Hz, three‐phase AC source. If

the load is purely resistive, then peak

instantaneous output voltage is equal to

[GATE 2005, IIT‐Bombay]

(A) 400 V (B) 400 2 V

(C) 2

400 V3

(D) 400

V3

Q.23 A three phase diode bridge rectifier is feeding a

constant DC current of 100 A to a highly

inductive load. If three phase, 415 V, 50 Hz AC

source is supplying to this bridge rectifier then

the rms value of the current in each diode, in

ampere, is _____.

[GATE 2016 (Set ‐ 02), IISc Bangalore]

Statement for Linked Answer Questions 24 & 25 ::

A solar energy installation utilizes a three‐phase

bridge converter to feed energy into power

system through a transformer of 400 V/400 V, as

shown below. [GATE 2011, IIT‐Madras]

The energy is collected in a bank of 400 V

battery and is connected to converter through a

large filter choke of resistance 10 .

Q.24 The maximum current through the battery will

be

(A) 14 A (B) 40 A

(C) 80 A (D) 94 A

Q.25 The kVA rating of the input transformer is

(A) 53.2 kVA (B) 46.0 kVA

(C) 22.6 kVA (D) 19.6 kVA

Q.26 A six pulse thyristor rectifier bridge is connected

to a balanced 50 Hz three phase ac source.

Assuming that the dc output current of the

rectifier is constant, the lowest frequency

harmonic component in the ac source line

current is [GATE 2002, IISc Bangalore]

(A) 100 Hz (B) 150 Hz

(C) 250 Hz (D) 300 Hz

Q.27 A 3‐phase fully controlled bridge converter with

free‐wheeling diode is fed from 400 V, 50 Hz AC

source and is operating at a firing angle of 060 .

The load current is assumed constant at 10 A

due to high load inductance. The input

displacement factor (IDF) and the input power

factor (IPF) of the converter will be


(A) IDF = 0.867 IPF = 0.828

(B) IDF = 0.867 IPF = 0.552

(C) IDF = 0.5 IPF = 0.478

(D) IDF = 0.5 IPF = 0.318

Q.28 A three phase fully controlled bridge converter

is feeding a load drawing a constant and ripple

free load current of 10 A at a firing angle of 030 .

The approximate Total harmonic Distortion

Battery

Filter Choke

GATEACADEMY® 31 ThreePhaseACtoDCConverter

(%THD) and the rms value of fundamental

component of the input circuit will respectively

be [GATE 2008, IISc Bangalore]

(A) 31% and 6.8 A (B) 31% and 7.8 A

(C) 66% and 6.8 A (D) 66% and 7.8 A

Q.29 A solar cell of 350 V is feeding power to an ac

supply of 440 V, 50 Hz through a 3‐phase fully

controlled bridge converter. A large inductance

is connected in the dc circuit to maintain the dc

current circuit 20 A. If the solar cell resistance is

0.5 , then each thyristor will be reverse biased

for a period of [GATE 2006, IIT‐Kharagpur]

(A) 0125 (B) 0120

(C) 060 (D) 055

Q.30 A three‐phase, 440 V, 50 Hz ac mains fed

thyristor bridge is feeding a 440 V dc, 15 kW,

1500 rpm separately excited dc motor with a

ripple free continuous current in the dc link

under all operating conditions, neglecting the

losses, the power factor of the ac mains at half

the rated speed is

(A) 0.354 (B) 0.372

(C) 0.90 (D) 0.955

Common Data Questions 31 and 32 ::

A 3‐phase full converter bridge is connected to

supply voltage 230 V per phase, 50 Hz and

source inductance 4 mHsL . The load current

in DC side is constant 20 A. If load consist of DC

source emf of 400 V with internal resistance of

1 .

Q.31 The value of firing angle delay in degree is

_______.

Q.32 The value of overlap delay angle in degree is

_______.


A 3‐phase fully controlled bridge converter is

connected to 415 V supply having a reactance of

0.4 /phase and resistance of 0.08 /phase.

The converter is operating in the inverting mode

at a firing advance angle of 030 when LI is 50 A

and assume thyristor voltage drops of 1.5 V.

Q.33 The generator or battery voltage to supply all

the drops including source is _______ V.

Q.34 The overlap angle is __________ degree.

Q.35 The recovery angle is _________ degree.


Q.1 Figure shown below shows a battery charging

circuit suing SCRs. The input voltage from

neutral to any line is 230 V (rms) and firing

angle for thyristors is 030 .

The average charging current is _________ A.

Q.2 A fully controlled natural commutated 3‐phase

bridge rectifier is operating with a firing angle 030 , The peak to peak voltage ripple

expressed as a ratio of the peak output dc

voltage at the output of the converter bridge is

(A) 0.5 (B) 3

2

(C) 3

12

(D) 3 1

Q.3 A 3‐phase half wave diode rectifier, feeds RL

load with R 5 and L = 3 mH, the average

load current for a 3‐phase input voltage of 400

V, 50 Hz is

(A) 44 A (B) 54 A

(C) 64 A (D) 74 A

Q.4 In a 3‐phase half‐wave diode rectifier, if per

phase input voltage is 200 V, then the average

output voltage is

(A) 233.91 V (B) 116.95 V

(C) 202.56 V (D) 101.28 V

Q.5 In a 3‐phase full‐wave diode rectifier, if V is the

per phase input voltage, then average output

voltage is given by

(A) 1.169 V (B) 1.35 V

(C) 2.34 V (D) 3 V

5

A

B

C

N

A1

B1

C1

150 V3-ph

aser

sup

ply


Q.6 A three‐phase ac to dc diode bridge rectifier is

supplying from a three‐phase, 440 V source. The

rectifier supplies a purely resistive load. The

average dc voltage across the load will be

_________V.

Q.7 In a three‐phase full wave ac to dc converter, the

ratio of output ripple‐frequency to the supply‐

voltage frequency is

(A) 2 (B) 3

(C) 6 (D) 12

Q.8 A three pulse converter is feeding a purely

resistive load. What is the value of firing delay

angle , which indicates the boundary between

continuous and discontinuous mode of current

conduction?

(A) 00 (B) 030

(C) 060 (D) 0150

Q.9 A three‐phase full converter is supplying a

purely resistive load at 300 V d.c. for 0° firing

angle. The output voltage for 90° firing angle

would be

(A) 0 V (B) 40 V

(C) 50 (D) 100 V

Q.10 In a 3 controller bridge rectifier, the

maximum conduction of each Thyristor is

(A) 60° (B) 90°

(C) 120° (D) 150°

Q.11 The frequency of ripple in the output voltage of

a three phase controlled bridge rectifier depends

on

(A) Firing angle (B) Load inductance

(C) Load resistance (D) Supply frequency

Q.12 A 3‐phase full converter, fed from 3‐phase, 400

V, 50 Hz source, delivers power to load R, Each

SCR is triggered sequentially. If the peak value

of the instantaneous output voltage is 400 V, the

firing of 3‐phase full converter would be

(A) 030 (B) 045

(C) 060 (D) 075

Q.13 A 3‐phase full converter delivers power to a

load 50R . The source voltage is 400 V, 50

Hz. For a firing‐angle delay of 045 , the power

delivered to load R is

(A) 3200 W (B) 2918 W

(C) 4800 W (D) 5846.4 W



connected to 415 V (rms), 3‐phase, 50 Hz mains.

The load consists of a 250 V battery in series

with resistor of 10 . The output current of the

converter is 15 A ripple free.

Q.14 The average output voltage of the converter is

(A) 400 V (B) 500 V

(C) 600 V (D) 700 V

Q.15 The delay angle is

(A) 042.46 (B) 043.46

(C) 044.46 (D) 045.46

Q.16 The peak inverse voltage (PIV) across SCR is

(A) 585.9 V (B) 586.9 V

(C) 587.9 V (D) 588.9 V

Q.17 The average SCR current is

(A) 3 A (B) 4 A

(C) 5 A (D) 6 A

Q.18 The rms SCR current is

(A) 8.63 A (B) 8.64 A

(C) 8.65 A (D) 8.66 A

Q.19 The peak SCR current is

(A) 13 A (B) 14 A

(C) 15 A (D) 16 A

Common Data Question 20 to 23::

A 3‐phase full converter, fed from 3‐phase, 400

V, 50 Hz source, is connected to load 10R ,

350 VE and large inductance os that output

current is ripple free

Q.20 The power delivered to load for 030 is _____ W.

Q.21 Supply power factor for firing angle of 030 is _____

Q.22 The power delivered to load for

firing advance angle of 060 is _____ W

Q.23 Supply power factor for firing advance angle of 060 _______.

GATEACADEMY® 33 ThreePhaseACtoDCConverter

Common Data Questions 24 & 25 ::


fed from 440 V, 50 Hz main through a

transformer with leakage inductance per phase

equal to 2.5 mH. The output current of converter

is 18 A and output voltage is 250 V.

Q.24 The firing angle of SCRs is _________ degree.

Q.25 The time of commutation of SCRs is _____ sec .

Common Data Question 26 to 31::

A 3‐phase full converter delivers a ripple free

load current of 10 A with a firing angle delay of 045 . The input voltage is 3‐phase, 400 V 50 Hz.

Q.26 The distortion factor is _____ .

Q.27 The current distortion factor is _____ .

Q.28 The total harmonic distortion is _____%.

Q.29 The supply power factor is _____.

Q.30 The active input power is _____ W.

Q.31 The reactive input power is _____ VAR.


A 3‐phase fully controlled bridge rectifier is fed

from a 440 V, 3‐phase, 50 Hz mains through a

transformer with 2 : 1 turns ratio. The rectifier

supplies power to dc motor. The motor draws a

current of 10 A. If the delay angle of SCR is 030 ,

and motor resistance is 2.

Q.32 The output voltage of the rectifier is

(A) 442. 66 V (B) 443. 66 V

(C) 444. 66 V (D) 445. 66 V

Q.33 The peak inverse voltage of the SCR is

(A) 438.89 (B) 538.89

(C) 638.89 (D) 738.89

Q.34 The rms current of the SCR is

(A) 3.77 A (B) 4.77 A

(C) 5.77 A (D) 6.77 A


A 3 ‐ phase full converter is delivering a

constant load current of 50 A at 230 V dc when

its input is 3 ‐ phase, 415 V, 50 Hz source. If each

thyristor has a voltage drop of 1.1 volt when

conducting.

Q.35 The firing angle delay of SCR’s in degree is

______.

Q.36 The rms current of SCR’s in ampere is _____.

Q.37 The rms source current in ampere is _____.

Q.38 A converter which can operate both in 3‐pulse

and 6‐pulse modes in a

(A) 1‐phase full converter

(B) 3‐phase half‐wave converter

(C) 3‐phase semi converter

(D) 3‐phase full converter

Q.39 In a 3‐phase semiconverter, for firing angle less

than or equal to 060 , freewheeling diode

conducts for

(A) 090 (B) 060

(C) 030 (D) 00

Q.40 In a three‐phase semi‐converter, if firing angle is

less than or equal to 60°, then the duration of

conduction of each thyristor and diode would be

respectively

(A) 60° and 60° (B) 90° and 30°

(C) 120° and 120° (D) 180° and 180°

Q.41 In a 3‐phase semiconverter, for a firing angle

equal to 090 and for continuous conduction, each

SCR and diode conduct, respectively, for

(A) 0 030 ,60 (B) 0 060 ,30

(C) 0 090 ,90 (D) 0 030 ,30

Q.42 In a 3‐phase semiconverter, for a firing angle

equal to 090 and for continuous conduction,

freewheeling diode conducts for

(A) 030 (B) 060

(C) 090 (D) zero degree

Q.43 In a 3‐phase semiconverter, for firing angle

equal to 0120 and extinction angle equal to 0100

, none of the bridge elements conduct for

(A) 010 (B) 020

(C) 030 (D) 060

Q.44 In a 3‐phase semiconverter, the three SCRs are

triggered at an interval of

(A) 060 (B) 090

(C) 0120 (D) 0180

Q.45 The frequency of the ripple in the output voltage

of a 3‐phase semiconverter depends upon


(A) firing angle and load resistance

(B) firing angle and load inductance

(C) the supply frequency

(D) firing angle and the supply frequency

Q.46 The frequency of ripple in the output voltage of

three phase half controlled bridge rectifier

depends on the

(A) firing angle (B) load inductance

(C) load resistance (D) supply frequency

Q.47 In a 3‐phase controlled bridge rectifier, with an

increase of overlap angle the output dc voltage

(A) Decreases

(B) Increases

(C) Does not change

(D) Depends upon load inductance


A 3‐phase M‐3 converter, fed from 3‐phase,

400 V, 50 Hz supply, has a load 1 ,R

230 VE and large L so that load current of 15

A is constant. If source has an inductance of 4

mH.

Q.48 The firing angle in degree for inverter operation

is _____.

Q.49 The delay angle in degree is ______.

Q.50 The overlap angle in degree is _______.

Answer Keys


1. C 2. B 3. A 4. 232.474 5. 20.785

6. 565 7. 16.8 8. 0 9. 0 10. 28.798

11. 49.88 12. 0 13. 70.54 14. 3.098 15. 7.589

16. 5.163 17. 9.707 18. 0 19. 13.856 20. D

21. C 22. B 23. 57.73 24. B 25. C

26. C 27. C 28. B 29. D 30. A

31. 34.41 32. 8.798 33. – 515.698 34. 9.087 35. 20.9128


1. 19.95 2. A 3. B 4. A 5. A

6. 594.208 7. C 8. B 9. B 10. C

11. D 12. D 13. A 14. A 15. C

16. B 17. C 18. D 19. C 20. 5506.82

21. 0.82697 22. 2159.05 23. 0.4775 24. 63.676 25. 159.455

26. 0.707 27. 0.955 28. 31.084 29. 0.6751 30. 3819.72

31. 3719.72 32. D 33. B 34. C 35. 64 – 65

36. 28 – 29 37. 40 – 41 38. C 39. D 40. C

41. C 42. A 43. B 44. C 45. D

46. D 47. A 48. 142.763 49. 139.712 50. 2.508

Chapter 4

Chopper (DC to DC Converter)


Common Data Question for 1 to 4 ::

For step down chopper of given below figure, dc

source voltage = 230 V, load resistance = 10 .

Take a voltage drop of 2 V across chopper when

it is on. For a duty cycle of 0.4.

Q.1 The average output voltage is _____ V.

Q.2 The RMS output voltage is _____ V.

Q.3 The chopper efficiency is _____%

Q.4 The ac ripple voltage is _____ V.

Q.5 For eliminating fifth harmonic from the output

voltage wave of a dc chopper, the ripple factor

should be

(A) 1 (B) 2

(C) 3 (D) 4

Q.6 A chopper circuit, feed from an input voltage of

20 V dc, delivers a load power of 16 watts. For a

chopper efficiency of 0.8, the input current is

____A.

Q.7 A dc chopper is fed from 100 V dc. Its load

voltage consists of rectangular pulses of

duration 1 msec in an overall cycle time of 3

msec. The average output voltage and ripple

factor for this chopper are respectively

(A) 25 V, 1 (B) 50 V, 1

(C) 33.33 V, 2 (D) 33.33 V, 1

Q.8 Figure shows a chopper operating from a 100 V

dc input. The duty ratio of the main switch S is

0.8. The load is sufficiently inductive so that the

load current is ripple free. The average current

through the diode D under steady state is

[GATE 2004, IIT‐Delhi]

(A) 1.6 A (B) 6.4 A

(C) 8.0 A (D) 10.0 A

Q.9 Below figure shows a step‐down chopper

switched at 1 kHz with a duty ratio D = 0.5. The

peak‐peak ripple in the load current is close to

[GATE 2005, IIT‐Bombay]

(A) 10 A (B) 0.5 A

(C) 0.125 A (D) 0.25 A

Q.10 A chopper is employed to charge a battery as

shown in below figure. The charging current is 5

A. The duty ratio is 0.2. The chopper output

voltage is also shown in below figure. The peak

to peak ripple current in the charging current is

[GATE 2003, IIT‐Madras]

(A) 0.48 A (B) 1.2 A

(C) 2.4 A (D) 1 A

SV 0V

+

_

0i

Load

SW

Chopper

+

_

FD

L

100 V D 10

S

200 mH

5 i

100 V

12 V

20 mHL 5 A

dcV

Chopper

200 s

1 ms

dcV 60 V

t


Q.11 An ideal chopper is operating at a frequency of

500 Hz from a 60 V battery input. It is supplying

a load having 3 resistance and 9 mH

inductance. Assuming the load is shunted by a

perfect commutating diode and assuming

battery is loss less, what is the mean load

current at an on/off ratio of 1/1? [ESE 2008]

(A) 10 A (B) 15 A

(C) 20 A (D) None of the above

Q.12 A 120 V battery supplies RL load through a

chopper. A freewheeling diode is connected

across RL load having 5R and L = 60 mH.

Load current varies between 7 A and 9 A. The

time ratio /on offT T for this chopper is

(A) 0.5 (B) 1.0

(C) 1.5 (D) 2.0

Common Data Questions for 13 to 16 ::

Following figure shows the circuit schematic of

a chopper driven separately excited DC motor.

The single pole double‐throw switch operates

with a switching period T of 1 ms. The duty

ratio of the switch ( / )ONT T is 0.2. The motor

may be assumed lossless, with an armature

inductance of 10 mH. The motor draws an

average current of 20 A at a constant back emf of

80 V, under steady state [IAS 1995]

Q.13 The frequency of chopper current is _____ kHz.

Q.14 The maximum current of motor is _____ A.

Q.15 The minimum current of motor is _____ A

Q.16 The peak to peak ripple current of motor is

________ A.

Statement For Linked Answer Questions 17 & 18 ::

A chopper, fed from a 220 V dc source, is

working at a frequency of 50 Hz and is

connected to an R‐L load of 5R and L = 40

mH.

Q.17 The value of duty cycle at which the minimum

load current will be 5 A is _______.

Q.18 For the obtained value of duty ratio the ripple

factor is _________.


Consider type A chopper shown in below

figure.

The output voltage of the chopper consists of

rectangular pulses of 2 ms duration in an overall

cycle time of 5 ms. Internal resistance of the

battery is negligible.

Q.19 The ripple factor is _____.


Q.21 The rms value of output voltage is _____ V.

Q.22 The rms value of the fundamental component of

output voltage is _____ V.

Q.23 The ac ripple voltage is _____ V.


A type, step‐down chopper operates from a 110

V, DC supply and feeds an active load

consisting by 11 V DC source in series with a

resistance of 0.25 and inductance of 1 mH.

Assume 2500 secT and 1000 secont .

Q.24 Average output voltage is __________ V.

Q.25 Maximum value of output current is ________

A.

Q.26 Minimum value of output current is _______ A.

Q.27 RMS value of fundamental output voltage is

________ V.

Q.28 RMS value of third harmonic of output voltage

is ________ V.


For type‐A chopper, source voltage 220VsV ,

chopping frequency 500Hzf , 800 seconT ,

1R , 1mHL and E = 72 V.

400 V

ONT

OFFT

ON OFFT T T

0V

0i

fIE

L

200 V D

S

LOAD

0V

GATEACADEMY® 37 Chopper(DCtoDCConverter)

Q.29 The value of average output voltage is ____V.

Q.30 The value of average output current is ____A.

Q.31 The maximum value of steady state output

current is _______ A.

Q.32 The minimum value of steady state output

current is _______ A.

Q.33 A step up chopper has output voltage of two

times the input voltage. If chopping frequency is

2000 Hz, turn‐off time of SCR is ____ sec .

Q.34 A step up chopper has source voltage 50 V and

output voltage 100 V. If pulse width is 10 μsec ,

the chopping frequency will be _____ kHz.

Q.35 A step‐up chopper with a pulse‐width of

100 sec is operating from 230 V dc supply. The

average value of load voltage for a chopping

frequency of 2000 Hz is ____V.

Common Data Question for 36 & 37 ::

A step‐up chopper has input voltage of 220 V

and output voltage of 660 V. If the conducting

time of thyristor‐chopper is 100 sec .

Q.36 The pulse width of output voltage is ____ sec .

Q.37 In case output‐voltage pulse width is halved for

constant frequency operation, find the average

value of new output voltage is _____ V.

Q.38 A step‐up chopper is used to feed a load at 400

V dc from a 250 V dc source. The inductor

current is continuous. If the ‘off’ time of the

switch is 20 s , the switching frequency of the

chopper in kHz is ________.


Q.39 The semiconductor switch S in the circuit of

figure is operated at a frequency of 20 kHz and a

duty ration 0.5D .The circuit operates in the

steady state. The power transferred from the dc

voltage source 1V to 2V is _____ kW.


Q.40 A DC chopper is used in regenerative braking

mode of a dc series motor. The dc supply is 600

V, the duty cycle is 70%. The average value of

armature current is 100 A. It is continuous and

ripple free. What is the value of power feedback

to the supply? [ESE 2009]

(A) 3 kW (B) 9 kW

(C) 18 kW (D) 35 kW

Q.41 A buck converter, as shown in Figure (a) below,

is working in steady state. The output voltage

and the inductor current can be assumed to be

ripple free. Figure (b) shows the inductor

voltage Lv during a complete switching

interval. Assuming all devices are ideal, the

duty cycle of the buck converter is _____.

[GATE 2016 (EE), Set ‐ 1, IISc‐Bangalore]

Q.42 In the circuit shown, an ideal switch S is

operated at 100 kHz with a duty ratio of 50 %.

Given that ci is 1.6 A peak‐to‐peak and 0I is 5

A dc, the peak current in S is


100 H

100 V 200 V2V1V

S

gV0V RCD

LV

M

ONT OFFT

ST

t

LV

30 V

0

20 V

(a) (b)

D C

L

R

0ICi

0V

S

24 V


(A) 6.6 A (B) 5.0 A

(C) 5.8 A (D) 4.2 A

Q.43 A buck converter feeding a variable resistive

load is shown in the figure. The switching

frequency of the switch S is 100 Hz and the duty

ratio is 0.6. The output voltage 0V is 36 V.

Assume that all the components are ideal, and

that the output voltage is ripple‐free. The value

of R (in Ohm) that will make the inductor

current ( )Li just continuous is __________.

[GATE 2015, IIT‐Kanpur]

Q.44 In the following chopper, the duty ratio of

switch S is 0.4. If the inductor and capacitor are

sufficiently large to ensure continuous inductor

current and ripple free capacitor voltage, the

charging current (in Ampere) of the 5 V battery,

under steady‐state, is _______.


Q.45 Figure (i) shows the circuit diagram of a

chopper. The switch S in the circuit in figure (i)

is switched such that the voltage D

V across the

diode has the wave shape as shown in figure (ii).

The capacitance C is large so that the voltage

across it, is constant. If switch S and the diode

are ideal, the peak to peak ripple (in A) in the

inductor current is _____.


Fig. (i)

Fig. (ii)

Q.46 In the circuit shown in the figure, the switch is

operated at a duty cycle of 0.5. A large capacitor

is connected across the load. The inductor

current is assumed to be continuous.

The average voltage across the load and the

average current through the diode will

respectively be [GATE 2008, IISc‐Bangalore]

(A) 10 V, 2 A (B) 10 V, 8 A

(C) 40 V, 2 A (D) 40 V, 8 A

Q.47 For the switching converter shown in the

following figure, assume steady‐state operation.

Also assume that the components are ideal, the

inductor current is always positive and

continuous and switching period is sT . If the

voltage LV is as shown, the duty cycle of the

switch S is _______. [GATE 2015, IIT‐Kanpur]

Q.48 A self‐commutating switch SW, operated at

duty cycle δ is used to control the load voltage

as shown in the figure.

60V 36V+ +

SLi 5mH

0V R

20 V

S L

C3

5V

1 mH

100V C Load

S

DV

DV

100 V

00.05 0.1 0.15 0.2

(msec)t

4 ALI

0Vs

L D

20V Load

DI

S+

+–

LV 0V

C

RinV

L

sTLV

15 V

– 45 V

t

CCV LR

LV

dcV

L

SW

D


Under steady state operating conditions, the

average voltage across the inductor and the

capacitor respectively, are


(A) 0LV and 1

1C dcV V

(B) 2L dcV V

and 1

1C dcV V

(C) 0LV and 1C dcV V

(D) 2L dcV V

and 1C dcV V

. Common Data Questions for 49 & 50 .

In the figure shown below, the chopper feeds a

resistive load from a battery source MOSFET Q

is switched at 250 kHz, with a duty ratio of 0.4.

All elements of the circuit are assumed to be

ideal. [GATE 2013, IIT‐Bombay]

Q.49 The average source current in Amps in steady

state is,

(A) 3/2 (B) 5/3

(C) 5/2 (D) 15/4

Q.50 The peak‐to‐peak source current ripple in Amps

is

(A) 0.96 (B) 0.144

(C) 0.192 (D) 0.288

Q.51 A dc to dc converter shown in the figure is

charging a battery bank, 2B whose voltage is

constant at 150 V. 1B is another battery bank

whose voltage is constant at 50 V. The value of

the inductor. L is 5 mH and the ideal switch. S is

operated with a switching frequency of 5 kHz

with a duty ratio of 0.4. Once the circuit has

attained steady state and assuming the diode D

to be ideal, the power transferred from 1B to 2B

(in Watt) is __________ (up to 2 decimal places).


Q.52 The input voltage DCV of the buck‐boost

converter shown below varies from 32 V to 72 V.

Assume that all components are ideal, inductor

current is continuous, and output voltage is

ripple free. The range of duty ratio D of the

converter for which the magnitude of the

steady‐state output voltage remains constant at

48 V is [GATE 2017, IIT Roorkee]

(A) 2 3

5 5D (B)

2 3

3 4D

(C) 0 1D (D) 1 2

3 3D

Q.53 In the circuit shown all elements are ideal and

the switch S is operated at 10 kHz and 60% duty

ratio. The capacitor is large enough so that the

ripple across it is negligible and at steady state

acquires a voltage as shown. The peak current in

amperes drawn from the 50 V DC source is

_________. (Give the answer up to one decimal

place.) [GATE 2017, IIT Roorkee]

:: Common Data for Questions 54 & 55 ::

In below figure (a), the ideal switch S is

switched on and off with a switching frequency

10kHzf . The circuit is operated in steady

state at the boundary of continuous and

discontinuous conduction, so that the inductor

current i is as shown in figure (b).

20 Q

100 H

470 F12 V

5mH

150 VS1B 50 V2B

DLi

L

S

C V0

+

–

VDC

5 75V

0.6 mH

50 V

S



Figure (a)

Figure (b)

Q.54 The on‐time onT of the switch is

(A) 53.33 sec (B) 63.33 sec

(C) 73.33 sec (D) 83.33 sec

Q.55 The value of the peak current pI is

(A) 63.33 A (B) 73.33 A

(C) 83.33 A (D) 93.33 A

Q.56 The power electronic converter shown in the

figure has a single‐pole double‐throw switch.

The pole P of the switch is connected alternately

to throws A and B. The converter shown is a


(A) step‐down chopper (buck converter)

(B) half‐wave rectifier

(C) step‐up chopper (boost converter)

(D) full‐wave rectifier

Q.57 A DC‐DC buck converter operates in continuous

conduction mode. It has 48 V input voltage, and

it feeds a resistive load of 24 . The switching

frequency of the converter is 250 Hz. If switch‐

on duration is 1 ms, the load power is


(A) 48 W (B) 6 W

(C) 12 W (D) 24 W

Q.58 In a DC‐DC boost converter, the duty ratio is

controlled to regulate the output voltage at 48 V.

The input DC voltage is 24 V. The output power

is 120 W. The switching frequency is 50 kHz.

Assume ideal components and a very large

output filter capacitor. The converter operates at

the boundary between continuous and

discontinuous conduction modes. The value of

the boost inductor (in H ) is _______.


Q.59 A DC‐DC boost converter as shown in the figure

below is used to boost 360 V to 400 V at a power

of 4 kW. All devices are ideal considering

continuous inductor current, the rms current in

the solid state switch (S), in ampere, is _____.

[GATE 2016 (EE), Set‐2, IISc‐Bangalore]

Q.60 A buck boost DC‐DC converter, shown in the

figure below, is used to covert 24 V battery

voltage to 36 V DC voltage to feed a load of 72

W. It is operated at 20 kHz with an inductor of 2

mH and output capacitor of 1000 F . All devices

are considered to be ideal. The peak voltage

across the solid state switch (S), in volt, is _____.

[GATE 2016 (EE), Set‐2, IISc‐Bangalore]

Q.61 The circuit shown is meant to supply a resistive

load LR from two separate DC voltage sources.

The switches S1 and S2 are controlled so that

only one of them is ON at any instant. S1 is

turned on for 0.2 ms and S2 is turned on for 0.3

ms in a 0.5 ms switching cycle time period.

Assuming continuous conduction of the

S

100 V 100 H 500 V

SON OFF ON

i

pI

tonT off

T

A

P

inVoutV

L

B

360 V

10 mH

1mF 400 VS

Load

2 mH24 VS

36 V

Load


inductor current and negligible ripple on the

capacitor voltage, the output voltage 0V (in

Volt) across LR is ________.


Q.62 The figure shows two buck converters

connected in parallel. The common input dc

voltage for the converters has value of 100 V.

The converters have inductors of identical value.

The load resistance is 1 . The capacitor voltage

has negligible rippel. Both converters operate in

the continuous conduction mode. The switching

frequency is 1 kHz, and the switch control

signals are as shown. The circuit operates in the

steady state. Assume that the converters share

the load equally, the average value of 1s

i , the

current of switch 1S (in ampere), is ______ (up

to 2 decimal places).[GATE 2018, IIT Guwahati]


CCommon Data Question for 1 to 6 ::

A step‐down chopper, fed from 220 dc, is

connected to RL load with 10R and L = 15

mH. Chopper frequency is 1250 Hz and duty

cycle is 0.5.

Q.1 The minimum value of load current is ______ A.

Q.2 The maximum value of load current is ______ A.

Q.3 The maximum value of ripple current is _____

A.

Q.4 The average value of load current is _____ A.

Q.5 The RMS value of load current is _____ A.

Q.6 The rms value of chopper current is _____ A.

Common Data Questions for 7 to 10..

For class A chopper, if 200VsV , 1mHL ,

0.3R , 20VE , 2300 secT and

1000 secont

Q.7 Average value of load current is _____ A.

Q.8 Maximum value of output current is _____ A.

Q.9 Minimum value of output current is _____ A.

Q.10 The duty cycle at which the current waveform is

just continuous is _____.

Q.11 An RLE load is operating in a chopper circuit

from a 500 volt dc source. For the load, L = 0.06

H, R = 0 and constant E. For a duty cycle of 0.2,

____ Hz is the chopping frequency to limit the

amplitude of load current excursion to 10 A.

Q.12 For type‐A chopper, feeding on RLE load, The

maximum value of average current rating for

the thyristor in case load current remains

constant is

(A) 2

As

E

V R (B)

2

A2 s

E

V R

(C) 2

A4 s

E

V R (D)

2

A8 s

E

V R

Q.13 A step‐down chopper is operated in the

discontinuous conduction mode in steady state

with a constant duty ratio . If xt – extinction

time, sV dc source voltage, T = chopping

period and E = constant dc load voltage, then the

magnitude of the average output voltage is

given by

10 V

1SL

5V C LR 0V

2S

100 V +

–1 C

L1si

2S

1S

L

t

t1 ms0.5 ms

S2

S1

Switch control signals


(A) 1 xs

tV E

T

(B) 1 xs

tV E

T

(C) 1 xs

tV E

T

(D) 1sx

TV E

t

Q.14 A step down, chopper operates from a dc

voltage source and feeds a dc motor armature

with a back e.m.f bE . From oscilloscope traces, it

is found that the current increases for time rt ,

falls to zero over time ft and remains zero for

time 0t in every chopping cycle, then the average

dc voltage across the free‐wheeling diode is


(A) 0( )

s r

r f

V t

t t t (B)

0

( )

( )s r b f

r f

V t E t

t t t

(C) 0

0

( )

( )s r b

r f

V t E t

t t t

(D) 0

0

[ ]

( )s r b f

r f

V t E t t

t t t

Common Data Questions for 15 to 19 ..

A type, step‐down chopper operates from a

110V, DC supply and feeds an active load

consisting of 11 V DC source in series with a

resistance of 0.25 and inductance of 1 mH.

Assume 2500 secT and 1000 secont .

Q.15 Average output voltage is _____ V

Q.16 Maximum value of output current is _____ A.

Q.17 Minimum value of output current is _____ A.

Q.18 RMS value of fundamental output voltage is

_____ V.

Q.19 RMS value of third harmonic of output voltage

is _____ V.

Q.20 The chopper of figure has load resistance

0.2R , input voltage 220V volts and

battery voltage 0VE . The average load

current 200AaI , and the chopping frequency

is 200Hzf (T = 5ms). The value of load

inductance L , which would limit the maximum

load ripple current to 5%f of aI is _____ mH.

Q.21 In the chopper circuit shown in figure, the input

DC voltage has a constant value sV . The output

voltage 0V is assumed ripple‐free. The switch S

is operated with a switching time period T and a

duty ratio . What is the value of at the

boundary of continuous and discontinuous

condition of inductor current Li ?

[GATE 2002, IIT Bangalore]

(A) 0

1 sV

V (B)

4L

RT

(C) 2

1L

RT (D)

RT

L


The buck‐converter in has an input voltage of

14 VsV . The required average output voltage

is 0 6 VV and the peak‐to‐peak output ripple

voltage is15 mV . The switching frequency is

30 kHz . If the peak‐to‐peak ripple current of

inductor is limited to 0.6 A .

Q.22 The duty cycle of the converter is ______.

Q.23 The filter capacitance L is _________ H .

Q.24 The filter capacitance C is _____ F .


Consider the boost converter of the input

voltage to this converter is 6 V . The average

output voltage 0 18 VV and the average load

current 0 0.4 AI . The switching frequency is

20 kHz of 250 HL and 420 FC .

Q.25 The duty ratio is _________.

Q.26 The ripple current of inductor is _____ A.

Q.27 The peak current through inductor is _____ A.

Q.28 The ripple voltage of filter capacitance is ______

mV.

1S

1D

0.2R

L

0 VE

220V

sV

S

Li

L

C R 0V


. Common Data Questions for 29 to 31 .

Consider the buck‐boost converter of the input

voltage to this converter is 14 VsV . The duty

cycle 0.6 and the switching frequency is

25 kHz . The inductance 180 HL and filter

capacitance 220 FC . The average load

current 0 1.5 AI .


Q.30 The peak to peak output voltage is _____ V.

Q.31 The peak to peak current of inductor is _____ A.

Q.32 A step down chopper is operated in the

continuous conduction mode in steady state

with a constant duty ratio D. If 0V is the

magnitude of the dc output voltages if sV is the

magnitude of the dc input voltage, the ratio

0 sV / V is given by

(A) D (B) 1 – D

(C) 1

1 D (D)

1

D

D

Q.33 For a step‐down d.c. chopper operating with

discontinuous load current, what is the

expression for the load voltage? (K is duty ratio

of chopper)

(A) 0 . .d cV V K (B) 0 . . /d cV V K

(C) 0 . . / (1 )d cV V K (D) 0 . . (1 )d cV V K

Q.34 In a type‐A chopper, given that source voltage

100 V d.c. On –period 100μsec , OFF‐period

150 μ sec and load 2R , 5 mHL with

back emf 10 VE connected in series for

continuous conduction, average output voltage

and average output current will be respectively

(A) 40V and 15A

(B) 66.66 V and 28.33 A

(C) 60 Vand 25 A

(D) 40V and 20A

Q.35 A dc chopper is fed from a constant voltage

mains. The duty ratio of the chopper is

progressively increased while the chopper feeds

a RL load. The per unit current ripple would

(A) Increase progressively

(B) Decrease progressively

(C) Decrease to a minimum value at 0.5 and

then increase

(D) Increase to a maximum value at 0.5 and

then decrease

Q.36 In dc choppers, per unit ripple is maximum

when the duty cycle is

(A) 0.2 (B) 0.5

(C) 0.7 (D) 0.9

Q.37 In a chopper, for eliminating third harmonic

from the output voltage wave, the duty cycle

should be equal to

(A) 1/5 (B) 1/4

(C) 1/3 (D) 1/2

Q.38 A d.c. chopper has a resistive load of 10 ohms

and an input voltage of 220 V. When the

chopper switch is ‘ON’, its voltage drop is 2 V

and the chopping frequency is 1 KHz. If the

duty cycle is 50%, then the average output

voltage will be _____ V.

Q.39 A chopper operating at a fixed frequency is

feeding an R‐L load, As the duty ratio of the

chopper is increased from 25% to 75%, the ripple

in the load current

(A) Remains constant

(B) Decreases, reaches a minimum at 50% duty

ratio and then increases

(C) Increases, reaches a maximum at 50% duty

ratio and then decreases

(D) Keeps on increasing as the duty ratio is

increased

Q.40 An ideal chopper operating at a frequency of

500Hz, supplies a load having resistance of 3

ohms and inductance of 9 mH from a 60V

battery. The mean value of the load voltage for

on/off ratio of 4/1, (assuming that load is

shunted by a perfect commutating diode and

battery is loss‐less) is

(A) 240 V (B) 48 V

(C) 15 V (D) 4 V

Q.41 Type‐A chopper, fed from 200 V dc, is connected

to load 5R . This chopper operates with on

and off periods of 2 ms and 3 ms respectively.


The peak value of load current and ripple factor

are

(A) 16 A, 1.225 (B) 25.3 A, 1.225

(C) 24 A, 0.8165 (D) 40 A, 1.225

Q.42 In a step down chopper with continues

conduction input/output voltage and

input/output current waveforms are

(A) Continuous / discontinuous

Continuous / continuous

(B) Continuous / discontinuous

Discontinuous / continuous

(C) Continuous / continuous

Continuous / continuous

(D) Continuous / continuous

Discontinuous / continuous

Q.43

The circuit shown in the above figure will work

as which one of the following?

(A) Buck‐Boost converter

(B) Buck converter

(C) Boost converter

(D) Dual converter

Q.44 A chopper circuit is operating on TRC control

mode at a frequency of 2 kHz on a 230 V dc

supply. For output voltage of 170 V, the

conduction and blocking periods of a thyristor

in each cycle are respectively

(A) 0.386 ms and 0.114 ms

(B) 0.369 ms and 0.313 ms

(C) 0.390 ms and 0.110 ms

(D) 0.131 ms and 0.369 ms

S

L1V C R

2V


Answer Keys


1. 91.2 2. 144.2 3. 99.13 4. 111.7 5. B

6. 1 7. C 8. A 9. C 10. A

11. A 12. A 13. 1 14. 23.2 15. 16.8

16. 6.4 17. 0.328 18. 1.43 19. 1.2247 20. 80

21. 126.49 22. 85.63 23. 97.98 24. 44 25. 165.424

26. 99.935 27. 47.09 28. – 9.701 29. 103.95 30. 31.95

31. 81.5 32. 0 33. 250 34. 50 35. 1150

36. 50 37. 1320 38. 31.25 39. 1.25 40. C

41. 0.4 42. C 43. 2.5 44. 1 45. 2.5

46. C 47. 0.75 48. A 49. B 50. C

51. 12 52. A 53. 40 54. D 55. C

56. A 57. B 58. 24 59. 3.5 60. 60

61. 7 62. 12.5


1. 9.56 2. 12.48 3. 2.93 4. 11 5. 13.9

6. 9.8 7. 223.2 8. 280 9. 168.14 10. 0.1372

11. 133.33 12. C 13. B 14. C 15. 44

16. 165.44 17. 99.93 18. 47.1 19. 9.7 20. 27.5

21. C 22. 0.4285 23. 190 24. 166.67 25. 0.667

26. 0.8004 27. 1.6 28. 31.76 29. 21 30. 0.16

31. 1.87 32. A 33. A 34. A 35. D

36. B 37. C 38. 109 39. C 40. B

41. D 42. B 43. A 44. B

Chapter 5

Commutation Techniques


Q.1 A voltage commutated chopper circuit, operated

at 500Hz, is shown below.


If the maximum value of load current is 10 A,

then the maximum current through the main (M)

and auxiliary (A) thyristors will be

(A) M max A maxi 12A and i 10A

(B) M max A maxi 12A and i 2A

(C) M max A maxi 10A and i 12A

(D) M max A maxi 10A and i 8A


A voltage commutated chopper operating at 1

kHz is used to control the speed of dc motor as

shown in figure. The load current is assumed to

be constant at 10 A. [GATE 2006, IIT‐Kharagpur]

Q.2 The minimum time in sec for which the SCR M

should be ON is

(A) 280 (B) 140

(C) 70 (D) 0

Q.3 The average output voltage of the chopper will

be.

(A) 70 V (B) 47.5 V

(C) 35 V (D) 0 V

Q.4 Figure shows a chopper. The device 1S is the

main switching device. S2 is the auxiliary

commutation device. 1S is rated for 400 V, 60 A.

2S is rated for 400 V, 30 A. The load current is 20

A. The main device operates with a duty ratio of

0.5. The peak current through 1S is


(A) 10 A (B) 20 A

(C) 50 A (D) 40 A


A voltage commutated chopper given in below

figure has the following parameters :

220VsV , load circuit parameters : R = 0.5 , L

= 2 mH, E = 40 V.

Commutation circuit parameters :

20 HL , 50 FC , 800 seconT , 2000 secT

and 0i = constant load current is 80 A.

Assume the initial voltage across capacitor is 220

V according to polarity as shown in below figure.

1 mH

Load200 V

0.1 F

M

A

Mi 10 A

Li

Ai

A

2 mH

250V

Li

M

1 F

2S

1S

200 H

D200 V

2 F

20 A

GATEACADEMY® 47 CommutationTechniques

Q.5 Effective on period in sec is ____.

Q.6 Peak current through main thyristor MT is _____

A.

Q.7 Peak current through auxiliary thyristor AT is

____A.

Q.8 Circuit turn off time for MT is ___ sec .

Q.9 Circuit turn of time of AT is ____ sec

Q.10 Total commutation interval is _____ sec .

Q.11 Capacitor voltage at 150 sect after AT is

triggered is _____ V.

Q.12 Time needed to recharge the capacitor to voltage

sV is _____ sec .

Q.13 The circuit in the figure is a current commutated

dc – dc chopper where, MTh is the main SCR and

AUXTh is the auxiliary SCR. The load current is

constant at 10 A. MTh is ON. AUXTh is triggered at

0t . MTh is turned OFF between.


(A) 0 25s t s (B) 25 50s t s

(C) 50 75s t s (D) 75 100s t s


The L‐C circuit shown in the figure has an

inductance L=1mH and a capacitance C = 10 μF.

[GATE 2010, IIT‐Guwahati]

Q.14 The initial current through the inductor is zero,

while the initial capacitor voltage is 100 V. The

switch is closed at t = 0. The current i through the

circuit is.

(A) 35cos(5 10 ) At (B) 45sin(10 ) At

(C) 310cos(5 10 ) At (D) 410sin(10 ) At

Q.15 The L‐C circuit of Q.8 is used to commutate a

thyristor, which is initially carrying a current of 5

A as shown in the figure below. The values and

initial conditions of L and C are the same as in

Q.57. The switch is closed at t = 0. If the forward

drop is negligible, the time taken for the device to

turn off is.

(A) 52 sec (B) 156 sec

(C) 312 sec (D) 26 sec

Q.16 A voltage commutated circuit is shown in figure.

If the turn off time of the SCR is 50 s and a safety

margin of 2 is considered. What will be the

approximate minimum value of capacitor

required for proper commutation?


(A) 2.88 F (B) 1.44 F

(C) 0.91 F (D) 0.72 F

C

D L

FD

+

0V

MT

AT

FDi

R

L

E

0i

VS

230 V

10 F 25.28 H

Load

MT

AT

0t 100 VC

L

i

C 100 V

20

5A

L

100V

i0t

50

1Th

100 V

2Th

50



Q.1 For the circuit shown in below figure, the

condction time for thyristor in nanoseconds is

(A) 0.393 (B) 2.546

(C) 25.133 (D) 8.0

Q.2 For the circuit in below figure, the capacitor

voltage after SCR gets self‐commutated is

(A) 200 V (B) 400 V

(C) 300 V (D) 100 V

Q.3 For the circuit shown in below figure, the

voltage across thyristor, after it is self‐

commutated is

(A) zero (B) – 1.5 V

(C) – 200 V (D) – 400 V

Q.4 In the circuit of below figure, the peak thyristor

current is

(A) 100 mA (B) 50 mA

(C) 400 mA (D) 800 mA

Q.5 For the circuit shown in below figure, the peak

value of resonant current is twice the load

current. In case 200VsV , the magnitude of

voltage across the main thyristor, when it gets

turned off, is equal to

(A) 86.6 V (B) 100 V

(C) 173.2 V (D) 200 V

Q.6 In the current‐commutated chopper shown in

figure, thyristor T1 is conducting a load current.

When thyristor TA is turned off with capacitor

polarity as shown the capacitor current Ci would

flow through….. (thyristor T1/diode D1)

(A) Thyrsitor 1T (B) Diode 1D

(C) Both (A) and (B) (D) None of these

Q.7 Refer to the circuit in given figure. The maximum

time after which main SCR M get turn‐off in

sec is ______.

200V

T

16 μH

4 pF

200V

T

16 μH

4 pF

200V

T

16 μH

4 pF

200V

T

16 μH

4 pF

1T

CSV

AT

LD

R

SV

LOAD

D1

D2

C

L

1T

AT

iVA

M

A

200 V

16 F

64 H

70.7

A

R

L

E

GATEACADEMY® 49 CommutationTechniques

Common Data Question for 8 and 9 ::

A voltage commutated chopper is inserted

between a battery 150sV V and a load resistance

10LR . The circuit turn OFF time for main

thyristor 1T is 110 s and the maximum

permissible current through it is a 30 A.

Q.8 The commutating capacitor is _____ μF .

Q.9 The commutating inductor is _____ mH.


A current commutated chopper has the following

data :

Source voltage 220 Vdc, Peak commutating

current 1.8 times the load current,

Main SCR, 20 sqt , Factor of safety 2 ,

Load current 180 A

Q.10 The commutating inductor is _____ μH .

Q.11 The commutating capacitor is _____ μF .

Q.12 The peak capacitor voltage is _____ V.

Q.13 Thyristor T in the figure below is initially off and

is triggested with a single pulse of width 10 s . It

is given that 100

HL

and 100

HC

.

Assuming latching and holding currents of the

thyristor are both zero and the initial charge on C

is zero, T conducts for

(A) 10 s (B) 50 s

(C) 100 s (D) 200 s

Q.14 In a thyristor dc chopper, which type of

commutation results in best performance?

(A) voltage commutation

(B) current commutation

(C) load communication

(D) supply commutation

Q.15 In the circuit configuration shown in below

figure, the circuit turn‐off time for main

thyristor is 34.657 s . The value of capacitor C

required, in this circuit, is

(A) 5 F (B) 3.466 F

(C) 1.733 F (D) 10 F


The commutating components for a current‐

commutated chopper are 40 FC and

18 HL . DC source voltage is 220 V and load

current is constant at a value of 180 A during the

commutation interval.

Q.16 The circuit turn‐off time for main thyristor is

(A) 43.12 sec (B) 53.12 sec

(C) 63.12 sec (D) 73.12 sec

Q.17 The circuit turn‐off time for auxiliary thyristor is

(A) 48.71 sec (B) 58.71 sec

(C) 68.71 sec (D) 78.71 sec

Q.18 The total commutation interval is

(A) 203.176 sec (B) 303.176 sec

(C) 403.176 sec (D) 503.176 sec

Q.19 A two‐quadrant d.c. to d.c. chopper can operate

with which of the following load conditions?

1. + ve voltage, + ve current

2. – ve voltage, + ve current

3. – ve voltage, – ve current

4. + ve voltage, – ve current

VS

C

DL

1T

AT

LR

0I

C

L

T

15 V

1T

C

200 VAT

D

10


Select the correct answer using the code given

below :

(A) 1 only (B) 1 and 2

(C) 1 and 4 (D) 3 and 4

Q.20 A chopper can be used on

(A) pulse‐width modulation only

(B) frequency modulation only

(C) amplitude modulation only]

(D) both PWM and FM

Q.21 In PWM method of controlling the average

output voltage in a chopper,

1. on‐time onT is varied and chopping frequency

f is kept constant.

2. onT is kept constant and f is varied.

3. both onT and off‐time offT are varied and f is

kept constant.

4. offT is varied and T is kept constant.

From above, the correct statements are

(A) 1, 3 (B) 1, 3, 4

(C) 2, 3, 4 (D) 3, 4

Q.22 For the circuit in below figure, the peak value of

current through auxiliary SCR is twice that

through the main SCR. In case 100VsV ,

10 FC and constant load current = 40 A, the

circuit turn‐off time for main SCR, in

microseconds is

(A) 12.5 (B) 21.65

(C) 25 (D) 10

Q.23 Refer to the circuit in the figure. The maximum

current in the main SCR can be

(A) 200 A (B) 170.7 A

(C) 141.4 A (D) 70.7 A

Answer Keys


1. A 2. B 3. B 4. D 5. 1075

6. 427.85 7. 80 8. 137.5 9. 49.6 10. 275

11. 20 12. 275 13. C 14. D 15. A

16. A


1. C 2. B 3. C 4. A 5. C

6. A 7. 125 8. 15.86 9. 1.586 10. 13.86

11. 29.94 12. 342 13. C 14. B 15. A

16. B 17. C 18. A 19. C 20. D

21. B 22. B 23. B

1T

CSV

AT

LD

R

SV

M

A

200 V

16 F

64 H

70.7

A

R

L

E

Chapter 6

Inverter (DC to AC Converter)



Single‐phase half‐bridge inverter has resistive

load of 3R and the d.c. input voltage

50 V.dcV

Q.1 The rms output voltage at fundamental

frequency (in volts) is _____.

Q.2 The output power (in watts) is _______.

Q.3 The peak current of each thyristor (in amp) is

________.

Q.4 The average current of each thyristor (in amp) is

________.


The single‐phase half‐bridge inverter has a

resistive load of 10 and the center‐tap dc

input voltage is 96 V.

Q.5 The rms output voltage (in volts) is ________.

Q.6 The rms value of fundamental output voltage

(in volts) is ________.

Q.7 The fundamental power consumed by the load

(in watts) is ________.

Q.8 The rms power consumed by the load (in watts)

is ________.


A single‐phase half –bridge inverted has load

2R . And dc source voltage

115V2sV

Q.9 The power delivered due to 1T (in watts) is

________.

Q.10 The power delivered to the load due to

fundamental current (in watts) is ________.

Q.11 Forced commutation is required (Yes/No)


A single phase full bridge inverter has RLC load of

4 , 35 mH,LR L and 155 FC . The dc input

voltage is 230 V and he output is 50 Hz.

Q.12 The ratio of 03(peak)

01(peak)

i

i is ___________.

Q.13 The ratio of 02(peak)

01(peak)

i

i is __________.

Q.14 The power absorbed by the load (in watts) is

____.

Q.15 The fundamental output power (in watts) is

_____.

Q.16 The conduction time of thyristor (consider

fundamental component) in msec is _______.

Q.17 The conduction time of diode (consider

fundamental component) in msec is _______.


A single phase full bridge inverter is fed from a

dc source such that fundamental component of

output voltage is 230 V.

Q.18 The rms value of fundamental component of

current of thyristor ( 2 , 8 , 6L CR X X )

is _________ A.


current of diode ( 2 , 8 , 6L CR X X ) is

_________ A.

Q.20 A single phase voltage source inverter is feeding

a purely inductive load as shown in the figure.

0.1 H

0i200 V


The inverter is operated at 50 Hz in 0180 square

wave mode. Assume that the load current does

not have any dc component. The peak value of

the inductor current 0i will be


(A) 6.37 A (B) 10 A

(C) 20 A (D) 40 A

Q.21 A single‐phase full‐bridge voltage source

inverter feeds a purely inductive load, as shown

in Fig., where 1 2 3 4T ,T ,T ,T are power transistors

and 1 2 3 4D , D , D ,D are feedback diodes. The

inverter is operated in square‐wave mode with a

frequency of 50 Hz. If the average load current is

zero, the time duration of conduction of each

feedback diode in a cycle is


(A) 5 msec (B) 10 msec

(C) 20 msec (D) 2.5 msec


inverter operating in square wave mode

supplied a purely inductive load. If the inverter

time period is T, then the time duration for

which the feedback diodes conduct in a cycle is

(A) T (B) 2

T [ESE 2000]

(C) 4

T (D)

8

T

Q.23 In the converter circuit shown below, the

switches are controlled such that the load voltage

0 ( )v t is a 400 Hz square wave.

The RMS value of the fundamental component

of 0 ( )v t in volts is _________.



Single‐phase full‐bridge inverter of figure has a

resistive load of 3R and the d.c. input

voltage 50VdcV .

Q.24 The rms output voltage at fundamental

frequency (in volts) is ________.

Q.25 The output power (in watts) is ________.

Q.26 The average current through each thyristor (in

amp) is ________.

Q.27 The power delivered to load due to fundamental

component is _____ W.

Q.28 The Voltage Source Inverter (VSI) shown in the

figure below is switched to provide a 50 Hz,

square‐wave ac output voltage ( 0v ) across an R‐

L load. Reference polarity of 0v and reference

direction of the output current 0i are indicated

in the figure. It is given that 3 ,R

. [GATE 2013, IIT‐Bombay]

In the interval when 0 0v and 0 0i the pair of

devices which conducts the load current is

(A) 1 2,Q Q (B) 3 4,Q Q

(C) 1 2,D D (D) 3 4,D D

3T

2T

1T

4T

3D

2D

1D

4D

Ls

V

Load220 V

0 ( )v t

1S 3S

4S 2S

dcV

4Q

Q1

2Q

3Q

1D 3D

4D 2D

0v

0i

3R

9.55 mHL

dcV

4Q

Q1

2Q

3Q

1D 3D

4D 2D

0v0i R

L

GATEACADEMY® 53 Inverter(DCtoACConverter)

Q.29 Figure (a) shows an inverter circuit with a dc

source voltage sV . The semi‐conductor switches

of the inverter are operated in such a manner

that the pole voltages 10 20andV V are as shown in

Figure (b). What is the rms value of the pole‐to‐

pole voltage 12V ?


(a)

(b)

(A) 2

sV

(B) sV

(C)

2sV (D) sV

Q.30 A single‐phase voltage source inverter shown in

figure is feeding power to a load. The triggering

pulses of the devices are also shown in the

figure. [GATE 2014, IIT‐Kharagpur]

If the load current L

i is sinusoidal and is zero at

0, , 2 ......, the node voltage Ao

V has the

waveform

(A)

(B)

(C)

(D)

Q.31 A 3‐phase voltage source Inverter is operated in 0180 conduction mode. Which one of the

following statements is true?

[GATE 2005, IIT Bombay]

(A) Both phase‐voltage and line voltage will

have 3rd harmonic components

(B) Phase‐voltage will have 3rd harmonic

component but line‐voltage will be free from

3rd harmonic

(C) Line‐voltage will have 3rd harmonic

component but phase‐voltage will be free

from 3rd harmonic

(D) Both phase‐voltage and line‐voltage will be

free from 3rd harmonic component.

Q.32 A three phase voltage source inverter with ideal

devices operating in 0180 conduction mode is

feeding a balanced star‐connected resistive load.

The DC voltage input is dcV . The peak of the

fundamental component of the phase voltage is


sV 10V 20V

0

10V

sV

0 2

20V

sV

iLLoad BO AVDC

S1 S2

S3 S4

θ – θ

+ θ 2 + θ

S S1 4,

S S2 3,

t

t

θ – θ VAO

V /DC 2

–V /DC 2

t

θ – θ VAO

V /DC 2

t

θ – θ VAO

V /DC 2

t

θ – θ VAO

V /DC 2

–V /DC 2

t


(A) dcV

(B)

2 dcV

(C) 3 dcV

(D)

4 dcV

Q.33 A three‐phase Voltage Source Inverter (VSI) as

shown in the figure is feeding a delta connected

resistive load of 30 Ω/phase. If it is fed from a

600 V battery, with 1800 conduction of solid‐state

devices, the power consumed by the load, in

kW, is __________. [GATE 2016, IISc‐Bangalore]


In the 3‐phase inverter circuit shown, the load is

balanced and the gating scheme is 180°

conduction mode. All the switching devices are

ideal. [GATE 2012, IIT‐Delhi]

Q.34 The rms value of load phase voltage is

(A) 106.1 V (B) 141.4 V

(C) 212.2V (D) 282.8 V

Q.35 If the dc bus voltage 300 VdV , the power

consumed by 3‐phase load is

(A) 1.5 kW (B) 2.0 kW

(C) 2.5 kW (D) 3.0 kW

Q.36 A 3 VSI is, supplying pure resistive load,

operating in 0180 conduction mode if peak value

of thyristor current is 12 A , the rms value of

Thyristor currents is _____ A.

Q.37 A 3‐phase voltage source inverter is supplied

from a 600 V DC source as shown in the figure

below. For a star connected resistive load of 20

per phase, the load power for 0120 device

conduction, in kW, is ____________.



A Y‐connected load of 15 per phase is fed

from 420 V . DC source through a 3 bridge

inverter

Q.38 The rms load current for 0180 mode is _____ A.

Q.39 The rms thyristor current for 0180 mode is _____

A.

Q.40 The average thyristor current for 0180 mode is

_____ A.

Q.41 The output power for 0180 mode is _____ W.

Q.42 The rms load current for 0120 mode is _____ A.

Q.43 The rms thyristor current for 0120 mode is _____

A.

Q.44 The average thyristor current for 0120 mode is

_____ A.

Q.45 The output power for 0120 mode is _____ W.

Statement for Linked Answer Ques. for 46 and 47 ::

An inverter has a periodic output voltage with the

output waveform as shown in figure.

Q.46 When the conduction angle 0120 , the rms

fundamental component of the output voltage is


(A) 0.78 V (B) 1.10 V

(C) 0.90 V (D) 1.27 V

30

30

30600 V

= 20R

R

phv

R

1S

3S

5S

2S6S4S

dV

3-phase inverter 3-phase balanced load

600 V

20

20 20

+1

–1

0


Q.47 With reference to the output waveform given in

figure, the output of the converter will be free

from 5th harmonic when


(A) 072 (B) 036

(C) 0120 (D) 0150

Q.48 A single‐phase voltage source inverter is

controlled in a single pulse‐width modulated

mode with a pulse width of 0150 in each half

cycle. Total harmonic distortion is defined as

THD 2 2

1

1

100rmsV V

V

where 1V is the rms value of the fundamental

component of the output voltage. The THD of

output ac voltage wave form is


(A) 65.65 % (B) 48.42 %

(C) 31.83 % (D) 30.49 %


inverter (VSI) is fed from a 300 V battery. A

pulse of 0120 duration is used trigger the

appropriate devices in each half‐cycle. The rms

value of the fundamental component of the

output voltage, in volts, is


(A) 234 (B) 245

(C) 300 (D) 331

Q.50 A single‐phase inverter is operated in PWM

mode generating a single‐pulse of width 2d in

the centre of each half cycle as shown in figure.

It is found that the output voltage is free from 5th

harmonic for pulse width 0144 . The percentage

of 3rd harmonic present in the output voltage

03 01max( / )V V will be


(A) 0.0% (B) 19.6%

(C) 31.7% (D) 53.6%

Q.51 The figure shows one period of the output

voltage of an inverter. should be chosen such

that0 060 90 . If rms value of the

fundamental component is 50 V, then in degree is ______. [GATE 2014, IIT‐Kharagpur]


A 1 , 50 Hz full bridge inverter is controlled

using multiple pulse width modulation

technique. A triangular carrier wave with peak

value of 3 V, 1 kHz is compared to the reference

square wave with peak value of 1 V.

Q.52 The number of pulses per half cycle is _______.

Q.53 The modulation index is ________.

Q.54 The total pulse width per half cycle (in degree)

is ________.

Q.55 The width of each pulse (in degree) is ________.

Q.56 The spacing between two pulses (in degree) is

_________.

Q.57 The location of first point from center of pulse

(in degree) is ________.

Q.58 The figure below shows a half‐bridge voltage

source inverter supplying an RL‐load with

40R and 0.3

HL

. The desired

fundamental frequency of the load voltage is 50

Hz. The switch control signals of the converter

are generated using sinusoidal pulse width

modulation with modulation index 0.6M . At

50 Hz, the RL‐load draws an active power of

1.44 kW. The value of DC source voltage DCV in

volts is [GATE 2017, IIT Roorkee]

0

V

–V

2d

2d

0v

/2 3 /2

2

0

100V

–100 V –100 V –100 V

180 – 180

180 + 360 – 360

t(degree)

100V 100V

+–

+–DC

V

DCV

R L

1S

2S


(A) 300 2 (B) 500

(C) 500 2 (D) 1000 2

Q.59 The switches T1 and T2 in figure (a) are

switched in a complementary fashion with

sinusoidal pulse width modulation technique.

The modulating voltage ( ) 0.8sin(200 )mv t t V

and the triangular carrier voltage ( cv ) are as

shown in figure (b). the carrier frequency is 5

kHz. The peak value of the 100 Hz component

of the load current (i1), in ampere, is _________.


Q.60 A single‐phase bi‐directional voltage source

converter (VSC) is shown in the figure below.

All devices are ideal. It is used to charge a

battery at 400 V with power of 5 kW from a

source Vs = 220 V (rms), 50 Hz sinusoidal AC

mains at unity p.f. If its AC side interfacing

inductor is 5 mH and the switches are operated

at 20 kHz, then the phase shift (δ) between AC

mains voltage (Vs) and fundamental AC rms

VSC voltage (VC1), in degree, is _________.


Q.61 The output voltage of a single‐phase full bridge

voltage source inverter is controlled by unipolar

PWM with one pulse per half cycle. For the

fundamental rms component of output voltage

to be 75% of DC voltage, the required pulse

width in degrees (round off up to one decimal

place) is _______. [GATE 2019, IIT‐Madras]

Q.62 The single‐phase full‐bridge voltage source

inverter (VSI), shown in figure, has an output

frequency of 50 Hz. It uses unipolar pulse width

modulation with switching frequency of 50 kHz

and modulation index of 0.7. For inV = 100 V DC,

L = 9.55 mH, C = 63.66 μF, and 5R , the

amplitude of the fundamental component in the

output voltage 0V (in Volt) under steady‐state is

_____. [GATE 2015, IIT‐Kanpur]


Q.1

For a single‐phase, full‐bridge inverter

supplying power to a highly induction load as

shown above, the correct sequence of operation

of switches and diodes is

/2 250 VdcV

/2 250 VdcV

Li

1T

2T12R 16LX

100Hz

at

(a)

0.81

t

cv

mv

(b)

400 V1mFS

I SX

5mH

220 V AC

S

I

SV

S SI X1C

V

L

inV RV C R 0V

Full bridge VSI

2S

1S

4S

3S

2D

1D

4D

3D


(A) 1 4 3 2 1 4 3 2S S S S S S S S

(B) 1 4 1 4 2 3 2 3D D S S D D S S

(C) 1 3 1 4 4 2 2 3S D S S S D D D

(D) 2 4 4 1 1 3 3 2S D D D D S S S


A single‐phase bridge inverter, fed from 230 V

dc is connected to load 10R and 0.03 HL .

Q.2 The power delivered to load in case the inverter

is operating at 50 Hz with square wave output

will be

(A) 1333.7 W (B) 1166.6 W

(C) 888.8 W (D) 2330.3 W

Q.3 The power delivered to load in case the inverter

is operating at 50 Hz with quasi‐square wave

output with an on‐period of 0.5 of a cycle will be

(A) 1333.7 W (B) 1163.2 W

(C) 888.8 W (D) 2333.7 W


A single‐phase full‐bridge inverter is fed from a

dc source such that fundamental component of

output voltage is 230 V.

Q.4 The rms value of thyristor current due to

fundamental component when load is

2R is _____ A.

Q.5 The rms value of diode current due to

fundamental component when load is 2R is

_____ A.


The full‐bridge inverter has a source voltage

220 VsV . The inverter supplies an RLC load

with 10R ohm, 10 mHL and and 52 FC .

The inverter frequency is 400 Hz.

Q.6 The rms load current at fundamental frequency

is _____ A.

Q.7 The rms load current is _____ A.

Q.8 The average supply current is _____ A.

Q.9 The average output power is _____ W.

Q.10 A single‐phase bridge inverter delivers power to

a series connected RLC load with 2R and

10 .L the periodic time 0.1T msec. What

value of C should the load have in order to

obtain load commutation for the SCRs. The

thyristor turn‐off time is 10μsec. Take circuit

turn off time as 1.5 .qt Assume that load current

contains only fundamental component.

(A) 1.481 F (B) 1.648 F

(C) 1.812 F (D) 1.248 F


A three‐phase bridge inverter is fed from a 500

V dc source. The inverter is operated in 0180

conduction mode conduction mode and it is

supplying a purely resistive, star‐connected

load.

Q.11 The rms line voltage is _____ V.

Q.12 The rms phase voltage is _____ V.


phase voltage is _____ V.


line voltage is _____ V.


A three‐phase bridge inverter is fed from 200 V

dc source. The inveter is operated in 0180

conduction mode and it is supplying inductive,

star‐connected load with 10R , and

20 mHL . The inverter frequency is 0 50 Hzf

Q.15 The rms line voltage is _____ V.

Q.16 The rms phase voltage is _____ V.

Q.17 The rms line voltage at fundamental frequency

is _____ V.

Q.18 The rms phase voltage at fundamental

frequency is _____ V.

Q.19 The total harmonic distortion (THD) is _____ %.

Q.20 The distortion factor is _____ %.

Q.21 The harmonic factor of the lowest order

harmonic is _____ %.

Q.22 The distortion factor of the lowest order

harmonics is _____ %.

Q.23 The load power is _____ W.

Q.24 The average switch current is _____ A.

Q.25 In single‐pulse modulation of PWM inverters,

fifth harmonic can be eliminated if pulse width

is equal to


(A) 030 (B) 060

(C) 0120 (D) 0150

Q.26 In multiple‐pulse modulation used in PWM

inverters, the amplitudes of reference square

wave and triangular carrier wave are

respectively 1 V and 2 V. For generating 5 pulses

per half cycle, the pulse width should be :

(A) 036 (B) 024

(C) 018 (D) 012

Q.27 A constant current source inverter supplies 20 A

to a load resistance of 1 . If the load resistance

is changed to 5 , then the load current

(A) Remains same at 20 A whereas the load

voltage changes to 100 V

(B) Changes to 4 A from 20 A and the load


(C) Changes to 4 A from 20 A and the load


(D) And load voltage stay at 20 A and 20 V

respectively

Q.28 A voltage source inverter is used when source

and load inductances are respectively

(A) Small and large (B) Large and small

(C) Large and large (D) Small and small

Q.29 A single phase, voltage source, square wave

inverter feeds a pure inductive load. The

waveform of the current will be

(A) Sinusoidal (B) Rectangular

(C) Trapezoidal (D) Triangular

Q.30 A single‐phase inverter has square wave output

voltage. The percentage of the fifth harmonic

component in relation to the fundamental

component will be

(A) 40% (B) 30%

(C) 20% (D) 10%

Q.31 A single‐phase, half‐bridge inverter has input

voltage of 48V DC. Inverter is feeding a load of

2.4 . The rms output voltage at fundamental

frequency is

(A) 2 48V

(B)

2 48V

2

(C) 2 48V

(D) 2 48V

2 2

Q.32 Compared to a single‐phase half‐bridge inverter,

the output power of a single‐phase full‐bridge

inverter is higher by a factor of

(A) 12 (B) 8

(C) 4 (D) 2

Q.33 In an inverter with fundamental output

frequency of 50 Hz, if third harmonic is

eliminated, then frequencies of other

components in the output voltage wave, in Hz,

would be

(A) 250, 350, 450, high frequencies

(B) 50, 250, 350, 450

(C) 50, 250, 350, 550

(D) 50, 100, 200, 250

Q.34 In a 1‐phase bridge inverter, the maximum

value of fundamental component of load current

is I. For a load which is highly inductive in

nature, the maximum value of nth harmonic

component of load current would be

(A) I

n (B)

I

n n

(C) 2

I

n (D) I


A single‐phase half‐bridge inverter has a

resistive load of 3R and the dc input voltage

24sV volts.

Q.35 The total harmonic distortion (THD) is _____ %.

Q.36 The distortion is _____ %.

Q.37 The harmonic factor of the third harmonics is

_____ %

Q.38 The distortion factor of lowest order harmonics

is _____ %.

Q.39 For a 3‐phase bridge inverter in 0180 conduction

mode, figure the sequence of SCR conduction in

the first two steps, beginning with the initiation

of thyristor 1, is

(A) 6, 1, 2 and 2, 3, 1 (B) 2, 3, 1 and 3, 4, 5

(C) 3, 4, 5 and 5, 6, 1 (D) 5, 6, 1 and 6, 1, 2

Q.40 For a 3‐phase bridge inverter in 0120 conduction

mode, figure the sequence of SCR conduction in

the first two steps, beginning with the initiation

of thyristor 1, is


(A) 6, 1 and 1, 2 (B) 1, 2 and 2, 3

(C) 1, 6 and 5, 6 (D) 1, 3 and 3, 4

Q.41 In three‐phase 0180 mode bridge inverter, the

lowest order harmonic in the line to neutral

output voltage (fundamental frequency output =

50 Hz) is

(A) 100 Hz (B) 150 Hz

(C) 200 Hz (D) 250 Hz

Q.42 A PWM switching scheme is used with a three

phase inverter to

(A) Reduce the total harmonic distortion with

modest filtering

(B) Minimize the load on the DC side

(C) Increases the life of the batteries

(D) Reduce low order harmonics and increase

high order harmonics

Q.43 A d.c. source is switched in steps to synthesize

the three‐phase output. The basic three‐phase

bridge inverter can be controlled. The angle

through which each switch conducts, and at any

instant the number of switches conducting

simultaneously are, respectively

(A) 0120 and 02 (B) 0120 and 03

(C) 0180 and 02 (D) 0180 and 04

Q.44 PWM switching is preferred in voltage source

inverters for the purpose of

(A) Controlling output voltage

(B) Output harmonics

(C) Reducing filter size

(D) Controlling output voltage, output

harmonics and reducing filter size


third harmonic can be eliminated if pulse width

is equal to

(A) 030 (B) 060

(C) 0120 (D) 0150

Q.46 In single‐pulse modulation used in PWM

inverters, sV is the input dc voltage. For

eliminating third harmonic, the magnitude of

rms value of fundamental component of output

voltage and pulse width are respectively

(A) 02 2V ,120s

(B) 06V ,60s

(C) 02 2V ,60s

(D) 06V ,120s

Q.47 In multiple‐pulse modulation used in PWM

inverters, the amplitude and frequency for

triangular carrier and square reference signals

are respectively 4 V, 6 kHz and 1 V, 1 kHz. The

number of pulses per half cycle and pulse width

are respectively

(A) 06,90 (B) 03,45

(C) 04,60 (D) 03,40

Q.48 In sinusoidal‐pulse modulation used in PWM

inverters, amplitude and frequency for

triangular carrier and sinusoidal reference

signals are respectively 5 V, 1 kHz and 1 V, 50

Hz. If zeros of the triangular carrier and

reference sinusoid coincide, then the modulation

index and order of significant harmonics are

respectively

(A) 0.2, 9 and 11 (B) 0.4, 9 and 11

(C) 0.2, 17 and 19 (D) 0.2, 19 and 21

Q.49 In sinusoidal‐pulse modulation used in PWM

inverters, amplitude and frequency of triangular

carrier and sinusoidal reference signals are

respectively 5 V, 1 kHz and 1 V, 50 Hz. If peak

of the triangular carrier coincides with the zero

of the reference sinusoid, then the modulation

index and order of significant harmonics are

(A) 0.2, 9 and 11 (B) 0.4, 9 and 11

(C) 0.2, 17 and 19 (D) 0.2, 19 and 21

Q.50 Simplest method of eliminating third harmonic

from the output voltage waveform of a single‐

phase bridge inverter is to use

(A) Inverters in series

(B) Single‐pulse modulation

(C) Stepped‐wave inverters

(D) Multiple‐pulse modulation

Q.51 A PWM switching scheme is used in single‐

phase inverters to

(A) Reduce the total harmonic distortion with

modest filtering

(B) Minimize the load on the dc side


(C) Increase the life of the batteries

(D) Reduce low‐order harmonics and increase

high‐order harmonics.


the pulse width is 0120 . For an input voltage of

220 V dc, the r.m.s. value of output voltage is

(A) 179.63 V (B) 254.04 V

(C) 127.02 V (D) 185.04 V

Q.53 Statement (I) : The output current of a current

source inverter remains constant irrespective of

load.

Statement (II) : The load voltage in CSI depends

on the load impedance.

Codes :

(A) Both Statement (I) and Statement (II) are

individually true and Statement (II) is the

correct explanation of Statement (I).

(B) Both Statement (I) and Statement (II) are

individually true but Statement (II) is NOT

the correct explanation of Statement (I).

(C) Statement (I) is true but Statement (II) is

false.

(D) Statement (I) is false but Statement (II) is

true.

Q.54 Which of the following statement/statements

is/are correct in connection with inverters

(A) VSI and CSI both require feedback diodes

(B) Only CSI requires feedback diodes

(C) GTOs can be used in CSI

(D) Only VSI requires feedback diodes.

Q.55 In a CSI, if frequency of output voltage is f Hz,

then frequency of voltage input to CSI is

(A) f (B) 2 f

(C) / 2f (D) 3 f

Q.56 A single‐phase CSI has capacitor C as the load.

For a constant source current, the voltage across

the capacitor is

(A) Square wave (B) Triangular wave

(C) Step function (D) Pulsed wave


Answer Keys


1. 22.5 2. 208.33 3. 8.33 4. 4.165 5. 96

6. 86.43 7. 747.01 8. 921.6 9. 3306.25 10. 5359.85

11. Yes 12. 0.1302 13. 0.0 14. 1634.63 15. 1604.27

16. 6.265 17. 3.735 18. 54.82 19. 17.33 20. B

21. A 22. C 23. 198 24. 45 25. 833.33

26. 8.33 27. 675.47 28. D 29. B 30. D

31. D 32. B 33. 24 34. B 35. D

36. 6 37. 9 38. 13.19 39. 9.33 40. 6.22

41. 7839.92 42. 11.43 43. 8.08 44. 4.66 45. 5879.98

46. A 47. A 48. C 49. A 50. B

51. 77.17 52. 10 53. 0.33 54. 120 55. 12

56. 5.45 57. 11.45 58. C 59. 10 60. 9.21

61. 112.82 62. 62.87


1. B 2. D 3. B 4. 81.31 5. 0

6. 9.83 7. 9.88 8. 4.43 9. 976.46 10. D

11. 408.24 12. 235.70 13. 225.07 14. 389.84 15. 163.29

16. 94.28 17. 155.93 18. 90.03 19. 31.15 20. 4.49

21. – 20 22. – 0.8 23. 1752.92 24. 3.1673 25. B

26. C 27. A 28. C 29. D 30. C

31. A 32. C 33. C 34. C 35. 49.34

36. 11.98 37. 0.18 38. 3.70 39. D 40. A

41. D 42. D 43. B 44. D 45. C

46. D 47. B 48. C 49. D 50. B

51. D 52. A 53. A 54. D 55. B

56. B

Chapter 7

AC Voltage Regulator

Introduction: AC voltage regulator are thyristor based devices which convert fixed alternating voltage directly to

variable alternating voltage without a change in the frequency.

Application of AC Voltage Regulators :

(i) Voltage control in power system (ii) Reactive power compensation (iii)Room heater

Types of AC Voltage Regulators : (iv) Single Phase Half Controlled ACVR (v) Single Phase Full Controlled ACVR (vi) Integral Cycle Control

SinglePhaseHalfControlledACVR: Single phase half controlled ACVR circuit consist of one thyristor in antiparallel with one diode.

During positive half cycle of input supply voltage SV , the thyristor 1T gets forward biased and can

be fired at any delay angle ( ) by applying gate pulse.

Once 1T is fired, the load get connected to source for rest of the portion of half cycle ( to ) .

During negative half cycle, the thyristor 1T remains OFF as it is reversed biased. But diode 1D get

forward biased and conducts for whole half cycle, i.e. from to 2t .

(1) During Positive Half Cycle (0 )t

(i) Mode – I (0 )t

Thyristor 1T OFF (Forward blocking mode)

Diode D OFF (Reverse biased)

ACVR Controlled ACUncontrolled AC

0isi

1Ti

Di

0VRsins mV V t

1T

D

0 As

i

0VRsinm

V t

GATEACADEMY® 63 ACVoltageRegulator

0 0S T Di i i i

0 0 0V i R

(ii) Mode – II ( )t

Thyristor 1T ON (Forward conducting mode)

Diode D OFF (Reverse Biased)

1

00T s

Vi i i

R

0 sins mV V V t

0Di

(2) During Negative half cycle ( 2 )t

Thyristor 1T OFF (Reverse biased)

Diode D ON (Forward biased)

0 sins mV V V t

00 D s

Vi i i

R

1

0Ti

0isi

0VRsinm

V t

1Ti

0isi

0VRsinm

V t

Di

SV

mV

0V

mV

t

t

t

mI

0i

sinm

V

2

2 3 4

2

2 3 4

2

2 3 4

T T

D D

sinm

I


Performance parameters :

(i) RMS output voltage is given by,

12 2

20 0

1

2rV V d t

1

2

0

1 1(2 ) sin 2

2 2m

r

VV

(ii) RMS value of output current is given by,

00

rr

VI

R

(iii)Average output voltage 0V is given by,

2

0

1sin

2 mV V t d t

0 [cos cos 2 ]2

mVV

0 [cos 1]2

mVV

(iv) Average load current/source current is given by,

00 ( )/ (cos 1)

2m

S avg

V VI I

R R

(v) Input power factor/Supply power factor is given by,

0 0 0SPF r r r

S S S

V I V

V I V 0( )r SI I

1

2sin 2(2 )

22SPF

2

m

m

V

V

1

21 sin 2SPF (2 )

22

(vi) Average value of thyristor current is given by,

( )

1sin

2m

T avg

VI t d t

R

( ) [cos cos ]2

mT avg

VI

R

( ) [1 cos ]2

mT avg

VI

R

(vii) RMS value of thyristor current is given by,

2

( )

1sin

2m

T rms

VI t d t

R


1

2

( )

sin 2

22m

T rms

VI

R

(viii) Average value of diode current is given by,

2

( )

1sin

2m

D avg

VI t d t

R

( ) [cos cos 2 ]2

mD avg

VI

R

( ) [ 1 1]2

m mD avg

V VI

R R

(ix) RMS value of diode current is given by,

22

( )

1sin

2m

D rms

VI t d t

R

1

2( ) [2 ]

2m

D rms

VI

R

( ) 2m

D rms

VI

R

SinglePhaseFullControlledACVR The controller becomes a full wave or bidirectional controller when power flow can be controlled in

both half cycles.

R load :

A single phase bidirectional controller employs two SCRs are connected in anti-parallel. The thyristor

1T conducts during positive half cycle of the input supply voltage and 2T conducts during negative half

cycle.

During positive half cycle 1T is triggered at a firing angle .

Once 1T is turned ON. At t , both source voltage and current falls to zero naturally and then

supply voltage is reversed. So, 1T is commutated at t .

During negative half cycle, 2T is fired at 2,t T then conducts from ( )t to 2 .

(1) During Positive half cycle (0 )t

(i) Mode – I (0 )t


Thyristor 2T OFF (Reverse biased mode)

1 2 0 0s T Ti i i i

0 0 0V i R

sinm

V t

2T

1T

0i

0VR

S

V

Si


(ii) Mode – II ( )t

Thyristor 1T ON (Forward conduction mode)


0 sins mV V V t

10

sinms T

V ti i i

R

(2) During Negative half cycle (π<ωt<2π)

(i) Mode – III ( )t



2 10 0s T Ti i i i

0 0 0V i R

(ii) Mode – IV ( 2 )t


Thyristor 2T ON (Forward conduction mode)

0A

0VRsinm

V t

0isi

0VRsinm

V t

1Ti

0A

0VRsinm

V t

0isi

0VRsinm

V t

2Ti


0 sins mV V V t

2

00

sinms T

V V ti i i

R R

1

0Ti


(i) Average output voltage is given by,

2

0

1sin sin

2 m mV V t d t V t d t

0 [cos cos ] [cos( ) cos(2 )]2 2

m mV VV

0 [cos 1 cos 1] 02

mVV

(ii) RMS output voltage is given by,

20

1( sin )r mV V t d t

1

2

0

sin 2

22m

r

VV

(iii)RMS output current is given by,

1

20

0

sin 2( )

22r m

r

V VI

R R

(iv) Input power factor/supply power factor is given by,

0 0 0SPF r r r

S S S

V I V

V I V

1

21 sin 2SPF

2

SV

mV

0V

mV

t

t

t

/m

V R

0i

sinm

V

2

2 3 4

2

2

3

4

2

2

3

4

T1

3

T1

T2 T2

3

3


(v) Average value of thyristor current is given by,

1 ( )

1sin

2m

T avg

VI t d t

R

1 ( ) [cos cos ]

2m

T avg

VI

R

1 ( ) [1 cos ]

2m

T avg

VI

R

Similarly, 2 ( ) [1 cos ]

2m

T avg

VI

R

(vi) RMS value of thyristor current is given by,

2

( )

1sin

2m

T rms

VI t d t

R

1

2

( )

sin 2

22m

T rms

VI

R

(vii) Power delivered to load is given by,

20 0rP I R

(viii) Circuit turn-off time is given by,

cktt

cktt

RL load :

In steady state, current will lag voltage by certain angle , as shown in figure below.

where, 1tanL

R

Case 1 : 0( ), is controlledV

During zero to , 1T is forward biased. At t , 1T is triggered and 10 Ti i starts building up

through the load.

sinm

V t

2T

1T

0i

R

S

V

Si

L

0V

0V

t

0i


At , load and source voltages are zero 0 0SV V , but the current 0i is not zero because of the

presence of inductance in the load circuit.

Due to the stored energy in the inductor, thyristor continues to conduct until which is called

extinction angle. At , load current 0i reduces to zero.

After , 1T is reverse biased but not turned OFF because 0i is not zero.

At only, when 0i is zero the thyristor 1T is turned OFF as it is already reverse bias. After the

commutation of 1T at , a voltage of magnitude sinmV at once appears as a reverse bias across

1T and as a forward bias across 2T .

From to ( ) , no current exist in the power circuit therefore 1 20 0, and .T S T SV V V V V

Thyristor 2T is turned ON at ( ) current 20 Ti i starts building up in the reverse direction

through the load.

When 1T conducts, voltage drop across it appears as a reverse bias across 2T . Similarly when 2T conducts

2TV appears as a reverse bias across 1T .

where, 1tanL

R


(i) Average output voltage is

0 0V

(ii) RMS load voltage is

1

2

0

1 sin 2 sin 2

2 22S

r

VV

mV

SV

2 3

2 t

3

mV

0V

2 t

3

1T

2T

1T

2T

mI

0i

2 t

3


Case 2 : 0( ), is uncontrolledV

Current will be zero at which is greater than the value of (so firing pulse of 2T is

skipped and it will not conduct.

1tanL

R


(i) Average output voltage is

0 (cos cos )2

mVV

(ii) RMS load voltage is

1

2

0

1 sin 2 sin 2

2 2 2S

r

VV

IntegralCycleControl Integral cycle control, consist of switching ON the supply to load for an integral number of cycles

and then switching OFF the supply for further number of integral cycles.

In Integral cycle control, the load is connected to a source through a pair of thyristor connected in anti-parallel.

The thyristor is turned ON for an integral number of cycles (n) at zero voltage crossing of ac

input voltage and maintained OFF for another few cycles (m) by inhibiting the gate pulse.

The ON time ONt usually consists of an integral number of cycle (n). Hence this method is

referred as “Integral Cycle Control ”.

SV

2 3

2 t

3

mV

0V

t

sinm

V

0I

t

2 3

2

3

3

sinm

V t

2T

1T

0i

0VR

S

V

Si


Integral cycle control is also known as burst firing, zero voltage switching, ON-OFF control. This type of control is used in application having high mechanical time constant (Example :

Speed control drives) or high thermal time constant (Example : Industrial heating loads).

Performance parameters : (i) RMS load voltage is

2

20

0

( sin )2 ( )r m

nV V t d t

m n

2

0 (2 0)2 ( )

Sr

VV n

m n

0r S

nV V

n m

SV k

where, Dutycyclen

kn m

,

Integralnumber of cycle (ON cycle)n

Another cycle (OFFcycle)m

(ii) RMS load current 0rI /RMS source current (rms)SI is

For purely resistive load rms value of current will be,

00 ( )/ r

r S rms

VI I

R SV k

R

(iii)Input power factor/Supply power factor is

0 0 0SPF r r r S

S S S S

V I V V kk

V I V V

(iv) Peak thyristor current (max)TI is

(max)m

T

VI

R

(v) Average value of thyristor current is

2

2

3

3

4

4

5

5

6 7 8 9 101T

1T

1T

1T

1T

1T

2T

2T

2T

2T

2T

2T

0V

SV

n cycle ON m cycle OFF

mV

t

6t

1T

2T

1T

2T

1T 1T 1T

1Ti

n cycle ON m cycle OFF

mI

t


( )

0

sin( )2T avg m

nI I t d t

m n

( ) [cos 0 cos ]( )2

mT avg

nII

m n

( )

2

( )2m m

T avg

nI I nI

m n m n

( )m

T avg

kII

m

m

VI

R

(vi) RMS values of thyristor current is

2( )

0

1( sin )

2 ( )T rms mI n I t d tm n

2

( )

0

2 ( ) 2m

T rms

nII

m n

( ) 2m

T rms

I kI

Solved Example 1

A single phase half wave ac voltage controller feeds a load of 20R with an input voltage of 230

V, 50 Hz. Firing angle of thyristor is 045 . Determine :

(a) RMS value of output voltage

(b) Power delivered to load and input power factor

(c) Average input current

Sol. Given :

(i) 230 VSV , 2 230VmV

(ii) 0454

, 20R

(a) RMS value of load voltage is

1

2

0

1 sin 2(2 )

2 2m

r

VV

1

2

0

2 230 1 sin 2 452

2 4 2rV

0 224.715 VrV Ans.

(b) Load power is given by,

20 0rP I R

RMS value of load current is

00

224.715

20r

r

VI

R

0 11.2357 ArI


20 0rP I R 2(11.2357) 20

0 2524.81 WP Ans.

0 11.2357 AS rI I

Input volt ampere S SV I 230 11.2357 VA = 2584.211 VA

Input power factor 20Load power or output power

Input powerr

S S

I R

V I

2524.81

2584.211

IPF 0.977 (lag) Ans.

(c) The average output voltage 0V is given by,

00

2 230(cos 45 1)

2V

15.162 V

Average input current,

00

15.162

20

VI

R

0 0.758 AI Ans.

Solved Example 2

A single phase half wave ac voltage controller has input voltage of 230 V, 50 Hz and a load of 15R . For 6 cycles ON and 4 cycle OFF. Determine :

(a) RMS output voltage

(b) Input power factor

(c) Average and rms thyristor currents

Sol. Given :

(i) 230 VSV , 50Hzf

(ii) 15R

(a) RMS value of output voltage is

0r S

nV V

n m

ONcycle, OFFcyclen m

0

6230

6 4rV

6230

10

0 178.157 VrV Ans.

(b) Input power factor k6

6 4

n

n m


(c) Peak thyristor current mI is

230 2

15mI

21.684 A

Average value of thyristor current is

( )

0.6 21.684mT avg

kII

( ) 4.1413 AT avgI Ans.


RMS value of thyristor current is

( )

21.684 0.6

2 2m

T rms

I kI

( ) 8.398 AT rmsI Ans.

Solved Example 3 A single phase full wave ac voltage controller feeds a load of 20R with an input voltage of 230

V, 50 Hz. Firing angle for both the thyristor is 045 . Calculate :

(a) RMS value of output voltage (b) Load power and input power factor

(c) Average and rms current of thyristor

Sol. Given :

(i) 230 VSV , 2 230VmV

(ii) 0454

, 20R

(a) RMS value of output voltage is

1

2

0

1 sin 2( )

22m

r

VV

10 2

0

sin 2 451230

4 2rV

0 219.304 VrV Ans.

(b) Load power and input power factor is

Load power, 20 0rP I R

RMS value of load current is

00

219.304

20r

r

VI

R 10.9652A

20 0rP I R 2(10.9652) 20

0 2404.71WP Ans.

0 10.9652 AS rI I

Input power factor Output power

Input power (VA)

2404.71

230 10.9652


(c) Average thyristor current is

( )

1sin

2T avg mI V t d tR

( ) (1 cos )2

mT avg

VI

R

0( )

2 230(1 cos 45 )

2 20T avgI

( ) 4.418 AT avgI Ans.


RMS value of thyristor current is

1

22

( ) 2

1sin

2T rms mI V t d tR

1

2

( )

1 sin 2( )

2 2m

T rms

VI

R

10 2

( )

2 230 1 sin(2 45 )

2 20 4 2T rmsI

( ) 7.7524 AT rmsI Ans.

Solved Example 4 The triac circuit shown in figure controls the ac output power to the resistive load. The peak power

dissipation in the load is [GATE 2004, IIT Delhi]

(A) 3968 W (B) 5290 W (C) 7935 W (D) 10580 W

Sol. Given circuit is shown below,

Supply voltage, sin( t)s mV V

Peak value of input voltage mV is,

230 2 VmV

230 2 sin t4

10R

230 2 sins

V t 4

10R

0v

4

2

mV

3

2

2

sV

0

4

2

0v

mV

t

t0


Since 4

(firing angle), so peak voltage across resistive load is also mV .

Peak power dissipation in the load 2 2( ) (230 2 )

10580 W10

mV

R

Hence, the correct option is (D).

Solved Example 5 In the single phase voltage controller circuit shown in the figure, for what range of triggering angle

(), the output voltage ( 0V ) is not controllable? [GATE 2008, IISc Bangalore]

(A) 0 00 45 (B) 0 045 135 (C) 0 090 180 (D) 0 0135 180

Sol. Single phase AC voltage controller shown above is supplied from,

sins mV V t

Given circuit is shown below,

Load impedance,

L LZ R jX R j L Z

L power factor angle

50R , 50X

50 50LZ j

1 1 0tan tan (1) 45L

X

R

050 2 45LZ

The output voltage is controllable when ,L therefore 00 45 the output voltage is not

controllable. Hence, the correct option is (A).

Solved Example 6 A single phase SCR based ac regulator is feeding power to a load consisting of 5 resistance and 16

mH inductance. The input supply is 230 V, 50 Hz ac. The maximum firing angle at which the voltage across the device becomes zero all throughout and the rms value of current through SCR, under this operating condition, are [GATE 2014, IIT Kharagpur]

(A) 030 and 46A (B) 030 and 23 A (C) 045 and 23 A (D) 045 and 32 A

50

sV 0v

50j

50

sV 0v

50j


Sol. Given :

(i) Single phase SCR based AC regulator load consists 5 ,R 16mHL .

(ii) Supply 230V, 50Hz .

The load impedance,

Z R j L 2 2( )R L

2 3 25 (2 50 16 10 )Z

5 2Z

1tanL

ZR

3

1 0(2 50 16 10 )tan 45

5Z

05 2 45Z Z

The impedance angle of inductive load,

045

The range of firing angle for controlled operation,

0180

The maximum firing angle at which the voltage across the device becomes zero or for continuous

conduction of thyristor 0max 45 because if we provide firing angle less than 045 , switch will not be

fully controlled. If we provide 045 then voltage across switch will not be zero.

. Method 1 :

RMS value of current through SCR

2

1sin( )

2rms

mT

VI t d t

Z

2

2

1 cos2( )( )

2 2rms

mT

V tI d t

Z

( )2

2

sin 2( )

2 2 2rms

mT

V tI t

Z

sin 2( ) sin 2( )

22rms

mT

VI

Z

22rms

mT

VVI

ZZ

Where, 5 2Z

230 2mV

4

After substituting the above values the RMS value of current through SCR is,

23 ArmsTI

Hence, the correct option is (C).


. Method 2 :

Since, 1T and 2T conducts alternatively (each for half of the cycle) to carry the load current 0i

Rms load voltage in this condition,

230 Vor sV V

Rms load current,

230

A5 2

oror

VI

Z

So, thyrsistor current rms,

230

23 A2 2 5 2

ortr

II

Hence, the correct option is (C).

Solved Example 7

For the circuit shown in the figure below, assume that diodes 1 2,D D and 3D are ideal.

The DC components of voltages 1V and 2V respectively are [GATE 2017, IIT Roorkee]

(A) 0 V and 1 V (B) – 0.5 V and 0.5 V (C) 1 V and 0.5 V (D) 1 V and 1 V

Sol. Given figure is shown below,

During positive half cycle :

1D is forward biased, hence it will act as short circuit.

2 3andD D are reverse biased, hence it will act as open circuit.

1 2

( ) ( )

2

V t R V tV V

R R

[By voltage division rule]

R

1V

R2V

( ) sin(100 ) VV t t

1D

2D

3D

R

1V

R2V

( ) sin(100 ) VV t t

1D

2D

3D

R

1V

R2V( )V t


During negative half cycle :

2D and 3D are forward biased, hence it will act as short circuit.

1D is reverse biased, hence it will act as open circuit.

1 ( )V V t

2 0V

Waveform of 1 2andV V :

Average value of 1V :

2

1, 1

0

1( )

2avgV V d t

2

1,

0

1 1sin ( ) sin ( )

2 2 2avgV t d t t d t

2

1, 0

1 1cos cos

4 2avgV t t

1,

1 1(1 1) (1 1)

4 2avgV

1,

11 0.5

2avgV

Average value of 2V :

2

2, 2

0

1( )

2avgV V d t

R

1V

( )V t

( ) sinV t t

t2

t2

2

1V

t2

2

2V

0

0

0


2,

0

1sin ( )

2 2avgV t d t

2, 0

1cos

4avgV t

2,

10.5

2avgV

Hence, the correct option is (B).

Solved Example 8 A load resistance of 10 is fed through a 1-phase voltage controller from a voltage source of

200sin 314 .t For a firing angle delay of 090 , the power delivered to load in kW is

(A) 0.5 (B) 0.75 (C) 1 (D) 2

Sol. Given :

(i) 200sin 314SV t

(ii) 090 , 10R

RMS value of output voltage,

1

2

0r

sin 2( )

22mV

V

1 1

2 2

0

200 2000 100 V

2 22 2rV

Power delivered to load,

2 2

00

1001000 W

10rV

PR

0 = 1kWP Ans.

Solved Example 9 A single-Phase voltage controller is employed for controlling the power flow from 260 V, 50 Hz source

into a load consisting of 5R and 12L . The value of maximum rms load current and the

firing angle are respectively

(A) 020A,0 (B) 0260A,0

10.91 (C) 020 A,90 (D) 0260

A,9010.91

Sol. Given :

(i) 260 VSV , 50Hzf

(ii) 5R , 12L

RMS quantity will be maximum only when firing angle 00 . Ans.

For 00 ,

0V

mV

t 2 3 4


0 260 V2m

r

VV

Maximum value of rms current is

0 max 2 2

260 260

5 12S

r

VI

Z Z

0 max20 A

rI Ans.

Solved Example 10 A single-phase voltage controller feeds power to a resistance of 10 . The source voltage is 200V rms.

For a firing angle of 090 , the rms value of thyristor current in amperes is ________ A.

Sol. Given :

(i) 200V(rms)SV

(ii) 090 , 10R

2

( )

sin1

2m

T rms

V tI d t

R

1

2

( )

sin 2( )

22 2m

T rms

VI

R

1

2200 2

210 2

( )

10 2

2T rmsI

( ) 10 AT rmsI Ans.

Solved Example 11 The full wave AC voltage controller circuit shown in figure controls AC output power to the resistive

load. The peak power dissipation in the load is

(A) 10580 W (B) 10260 W (C) 3787 W (D) 5000 W

Sol. Given :

(i) 230 2 sinSV t

(ii) 0100 , 10R

Given circuit diagram is

230 2 sin t

2T

1T

10R

0100

230 2 sin t

2T

1T

0i

0V

S

V

Si

0100

10R


If 090 ,

Peak power dissipation in the load is

202

0(max)

230 2 sin (100 )( sin )

10mV

PR

0(max) 10260.9 WP Ans.

Solved Example 12

A single-phase voltage controller has input voltage of 240 V, 50 Hz and a load of 6 .R For 3 cycles

ON and two cycles OFF, the load would consume a power of

(A) 2880 W (B) 5760 W (C) 3456 W (D) 11520 W

Sol. Given :

(i) 240V(rms)SV , 6R

(ii) 3m , 2n

RMS Value of load voltage,

2

20

0

( sin )2 ( )r m

mV V t d t

m n

1 1

2 2

0

sin 2 0 sin 2 22 0

2 22 2m

r

V mV

m n

11

22

0

240 2[2 ]

2 2r

mV

m n

1

2

0

3240 185.90V

5rV

Power delivered to the load will be

2 20

0

185.90

6rV

PR

0 5759.80 WP Ans.

Solved Example 13

A single phase ac voltage regulation with RL load has the following details, 4 , 3LR X .

________ is the minimum firing angle for which output voltage is controllable.

Sol. Given : 4 Ω, 3 Ω, 230 VL SR X V

1 1 03tan tan 36.86

4

L

R

For output voltage is controllable. Range of firing angle will be

0180

0 036.86 180

036.86 is the minimum firing angle. Ans.


Solved Example 14

A single phase ac voltage controller is controlling current in a purely inductive load. If the firing angle of the SCR is , the conduction angle of the SCR will be

(A) (B) 2( ) (C) (2 ) (D) 2

Sol. Assuming conduction is continuous then for pure Inductive load, inductive Energy stored by inductor will be . So energy will release for . Hence, conduction angle for SCR should be 2( ).

Ans.


SPACEFORNOTES

edition 2020-21 power electronics

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