advanced techniques of pulse width modulation

AUDISANKARA

ADVANCED TECHNIQUES

OF

PULSE WIDTH

MODULATIONUnder the esteemed guidance of

A.N.V.K NAVEEN

BY

SUDHEER PUCHALAPALLI

112H1A0279

INSTITUTE OF TECHNOLOGY

H.O.D

M.NAGARAJU M.Tech.,(Ph.D.,)

CONTENTS

Need for voltage control

Traditional methods for inverter voltage control

Disadvantages of conventional methods

Pulse width modulation

Classification of pwm

Components used in vsi and csi

Single-pulse width modulation

Multiple-pulse width modulation

Sinusoidal pulse width modulation

Disadvantages with above techniques

Space vector pulse width modulation

Advantages of svpwm

Applications

conclusion

NEED FOR VOLTAGE CONTROL

Light dimming circuits for street lights

Industrial & domestic heating

Induction heating

transformer tap changing

Speed control of Motors (variable torque)

speed control of winding machines, fans

AC magnet controls

TRADITIONAL METHODS FOR INVERTER

VOLTAGE CONTROL

EXTERNAL CONTROL OF AC OUTPUT VOLTAGE

EXTERNAL CONTROL OF DC INPUT VOLTAGE

InverterAC Voltage

ControllerAC Load

InverterFilterFully

Controlled

rectifier

Constant

DC Voltage

Controlled

AC voltage

AC

voltage

Constant

AC VoltageDC

Voltage

Controlled

DC Voltage

Controlled

AC Voltage

DISADVANTAGES OF TRADITIONAL METHODS

Complexity increases

High cost

Occupies more space

Not flexible in control

Not compatible with user

Not commercial

Requires more floor area

Unique solution to above all problems is PULSE WIDTH MODULATION technique.

PULSE WIDTH MODULATION

The modulating of width of the pulse by

keeping height as constant.

The different time periods or pulses will be

given to power electronics devices.

Although this modulation technique can be

used to encode information for transmission.

Its main use is to allow the control of the

power supplied to electrical devices,

especially to inertial loads such as motors.

COMPONENTS USED IN VSI AND CSI

Silicon control rectifier(SCR)

Gate Turn off Thyristor(GTO)

Thyristors

Transistors

Bi-junction transistor(BJT)

Metal oxide semi-conductor device(MOSFET)

Static induction transistor(SIT)

Insulated gate bi-polar transistor(IGBT)

Pulse Width

Modulation

Single Pulse

Width

Modulation

Multiple Pulse

Width

Modulation

Sinusoidal

Pulse Width

Modulation

CLASSIFICATION OF PWM

SINGLE-PULSE WIDTH MODULATION

Single pulse for half cycle generates from this

techniques.

It consists of a pulse located symmetrical about π/2

and another pulse located symmetrical about 3π/2.

The shape of the output voltage is Quasi-Square wave.

Great deal of harmonic content is introduced in the output voltage.

The amplitude of harmonic content is 0.33 units.

Very poor performance at lower voltages.

CONTD.,

MULTIPLE-PULSE WIDTH MODULATION

It is an extension to single pulse width modulation.

More pulses will exist in an half cycle.

The width of every single pulse is same.

ComparatorTrigger pulse

generator

Triangular wave

Square wave

Trigger

pulses to

scr

lower order harmonics are

eliminated.

The magnitude of higher harmonics

would go up.

This has more applications than

single-pulse width modulation in

olden days.

CONTD.,

SINUSOIDAL PULSE WIDTH MODULATION

Pulses will have

different widths.

The width of the

individual pulse will

be decided

according to the

angular position of

sine wave.

CONTINUE

Height of the pulse is kept as constant

Odd multiple of 3 and even harmonics are suppressed

Popularly accepted pulse width modulation technique.

DISADVANTAGES OF ABOVE

PWM TECHNIQUES

Lesser utilization of DC supply voltage.

Higher harmonics

Lower modulation index

Less flexibility

Difficult in manipulation

Unique solution to above all problems is

SPACE VECTOR PULSE WIDTH MODULATION

technique.

SPACE VECTOR PULSE WIDTH MODULATION

Output voltages of three-phase inverter (1)

where, upper transistors: S1, S3, S5

lower transistors: S4, S6, S2

switching variable vector: a, b, c

tdc

ca

bc

ab

c]b[avectorvariableswitchingwhere,

c

b

a

101

110

011

V

V

V

V

c

b

a

211

121

112

V3

1

V

V

V

dc

cn

bn

an

Output voltages of three-phase inverter (2)

S1 through S6 are the six power transistors that shape the ouput voltage

When an upper switch is turned on (i.e., a, b or c is “1”), the corresponding lower

switch is turned off (i.e., a', b' or c' is “0”)

Line to line voltage vector [Vab Vbc Vca]t

Line to neutral (phase) voltage vector [Van Vbn Vcn]t

Eight possible combinations of on and off patterns for the three upper transistors (S1, S3, S5)

Output voltages of three-phase inverter (3)

The eight inverter voltage vectors (V0 to V7)

Output voltages of three-phase inverter (4)

The eight combinations, phase voltages and output line to line voltages

Principle of Space Vector PWM

This PWM technique approximates the reference voltage Vref by a combination

of the eight switching patterns (V0 to V7)

The vectors (V1 to V6) divide the plane into six sectors (each sector: 60 degrees)

Vref is generated by two adjacent non-zero vectors and two zero vectors

Coordinate Transformation (abc reference frame to the

stationary d-q frame)

: A three-phase voltage vector is transformed into a vector in the

stationary d-q coordinate

frame which represents the spatial vector sum of the three-phase

voltage

Treats the sinusoidal voltage as a constant amplitude vector rotating

at constant frequency

Basic switching vectors and Sectors

Fig. Basic switching vectors and sectors.

6 active vectors (V1,V2, V3, V4, V5, V6)

Axes of a hexagonal

DC link voltage is supplied to the load

Each sector (1 to 6): 60 degrees

2 zero vectors (V0, V7)

At origin

No voltage is supplied to the load

Comparison of Sine PWM and Space Vector PWM (2)

Space Vector PWM generates less harmonic distortion

in the output voltage or currents in comparison with sine PWM

Space Vector PWM provides more efficient use of supply voltage

in comparison with sine PWM

Voltage Utilization: Space Vector PWM = 2/3 times of Sine PWM

Realization of Space Vector PWM

Step 1. Determine Vd, Vq, Vref, and angle ()

Step 2. Determine time duration T1, T2, T0

Step 3. Determine the switching time of each transistor (S1 to S6)

cn

bn

an

q

d

V

V

V

2

3

2

30

2

1

2

11

3

2

V

V

frequency)lfundamentaf(where,

t2ππtω)V

V(tanα

VVV

s

ssd

q1

2q

2dref

Fig. Voltage Space Vector and its components in (d, q).

cnbnan

cnbnq

cnbnan

cnbnand

V2

3V

2

3V

cos30Vcos30V0V

V2

1V

2

1V

cos60Vcos60VVV

Step 1. Determine Vd, Vq, Vref, and angle ()

Coordinate transformation

: abc to dq

Fig. Reference vector as a combination of adjacent vectors

at sector 1.

Step 2. Determine time duration T1, T2, T0 (1)

Switching time duration at any Sector

Step 2. Determine time duration T1, T2, T0 (3)

60α0

6)toSector1is,(that6through1nwhere,,

3

1cossin

3

1sincos

3

3

1sin

3

sin3

coscos3

sin3

3sin

3

3

1

3sin

3

210

2

1

TTTT

nn

V

refVT

n

V

refVTT

nn

V

refVT

n

V

refVT

n

V

refVTT

z

dc

z

dc

z

dc

z

dc

z

dc

z

Fig. Space Vector PWM switching patterns at each sector.

(a) Sector 1. (b) Sector 2.

Step 3. Determine the switching time of each transistor (S1 to S6) (1)

Fig. Space Vector PWM switching patterns at each sector.

(c) Sector 3. (d) Sector 4.

Step 3. Determine the switching time of each transistor (S1 to S6) (2)

Fig. Space Vector PWM switching patterns at each sector.

(e) Sector 5. (f) Sector 6.

Step 3. Determine the switching time of each transistor (S1 to S6) (3)

Table 1. Switching Time Table at Each Sector

Step 3. Determine the switching time of each transistor (S1 to S6) (4)

APPLICATIONS

Power converters

Motor control

Ac machines control

UPS

Low power applications

CONCLUSION

Space vector pulse width modulation

is the best technique which is ruling

the world now.

Still a lot of research is going on this

svpwm.

It should be available with low cost

for household purpose.

Any queries…