lab-1a

7/29/2019 LAB-1a

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DEPARTMENT OF ELECTRICAL ENGINEERING

LAB WORK – ET502 POWER ELECTRONICS

EXPERIMENT : 1a

TITLE : TURN ON AND TURN OFF THYRISTOR CHARACTERISTIC (SIMULATION)

OUTCOME :

Upon completion of this unit, student should be able to:

i. Handle the practical work on the power electronics converters using appropriate

equipment. [CLO3](PLO2,LD2,P3)

OBJECTIVES :

1. Describe the turn-on and turn-off characteristics of a thyristor

2. Describe the turn-on and turn-off process of a thyristor

3. Find the turn-on time and turn-off time of a thyristor by Pspice simulation

BRIEF THEORY :

Silicon controlled rectifiers (SCRs), are one of the most popular and useful device among thyristors. It is

the most popular electrical power controller due to its fast switching action, small size and high current

and high voltage ratings. It has three terminals: the anode (A) and the cathode (K) are the power

terminals, and the gate (G) is the control terminal. When the SCR is forward-biased, that is when the

anode is made positive with respect to the cathode, a positive voltage on the gate with respect to turns

on (trigger) the SCR. However, the current through the SCR cannot be turned off using the gate. It is

turned off by interrupting the anode current. A pulse signal must be applied to the gate in order for the

SCR to conduct. If there is no pulse current at the gate, then the SCR will act as an open switch.

7/29/2019 LAB-1a


PART 1:

Thyristor Turn-on Characteristics

PROCEDURE :

1. Using Pspice, design and simulate the circuit in Figure 1.

2. Set the Vgateas shown in Figure 1.

3. Select Analysis menu, click on Setup. Then check Transient. After that click on Transient and give

the transient information: print step = 0.1ns and final time = 4.0us.

4. Run the simulation by choosing Simulate from the Analysis menu. Click on Trace> Add Trace. In

the trace expression box, type in –I(R1) and click OK.

5. Click on Plot > Add plot to window. After that, click on Trace > Add trace. In the trace

expression box, type inV(Rg:1) and click OK.

6. The graph you will see is the anode current (-I(R1)) and the gate voltage (V(Rg:1)). When the

gate voltage was applied, the anode current does not rise instantaneously. There was a delay

time of td and a rise time of tr. The turn-on time, ton = td +tr.

7. Measure the delay time and the rise time to calculate the turn-on time. Note: Take these

readings from the anode current graph (-I(R1)).

Note: To measure an interval from one point to another point, click on Trace>cursor>display. When

the window pops up, point the cursor at the first point and right click on mouse, then point the

cursor to the second point and left click on the mouse.

Note: To print out the value for each interval, click the Tab accordingly.

1. Click 1 – and point to the desired point.

2. Click 2 –

and the coordinate will pops up.

3. Click 3 – and type the name of the point

13 2

7/29/2019 LAB-1a


PART 2:

Thyristor Turn-off Characteristics

PROCEDURE :

1. Using Pspice, design and simulate the circuit in Figure 2.

2. Set the VSIN as shown in Figure 2.

3. Set the Vgate as shown in Figure 2.

4. Save the circuit and click on Analysis>Setup. Select Transient by check the box beside it. Click on

Transient and give the transient information: print step = 0.1ns and final time = 100us.

5. Simulate the circuit by select Analysis> Simulate. Click on Trace> Add trace. In the trace

expression box, type in V(R1:1) and press OK.


expression box, type inV(Rg:1) and click OK.


expression box, type in -I(R1).

8. The Pspice will plots the anode current –I(R1) and the anode-cathode voltage (V(R1:1). When

the anode current falls to zero, the thyristor still continues to conduct due to reverse recovery

time (Trr) similar to diode. The thyristor requires also an additional time known as turn-off time

Tq. This time interval is essential for the device before it can withstand any forward blocking

voltage, otherwise it will remain on and behave as a short-circuit.

9. On your graph, the anode current does not begin at t=0 and the anode-cathode voltage is

positive during this time interval, because of the delay time Td of the thyristor. You can see this

clearly if you zoom the (-I(R1) graph. The delay time is 0 to where it starts rising. The reverse

recovery time is the negative peak after the positive peak of (-I(R1)).

10. Change the frequency (FREQ) in step 1 to 25kHz and 40kHz and measure the gating period,

Delay time (Td), Reverse recovery time (Trr), rising time (Tr) and the Turn-off-time (Toff) for

frequency values of 20kHz, 25kHz and 40kHz.

Results:

As your result: print out:

1. The circuits you have designed complete with their Vgate and Vsin settings.

2. The graphs you have simulated both in Part 1 and Part 2 complete with labels indicating gating

period, Delay time (Td), Reverse recovery time (Trr), rising time (Tr) and the Turn-off-time (Toff).

3. Complete the chart below.

7/29/2019 LAB-1a


Part 1:

Figure 1: SCR turn on characteristics circuit

Part 2:

Figure 2: SCR turn off characteristics circuit

V1 = 0

V2 = 4V

PKGREF = Vgate

TD = 0

TR = 1ps

TF=1ps

PW = 1.2us

PER = 5.2us

V1 = 0V

V2 = 4V

TD = 0

TR = 1ps

TF=1ps

PW = 10us

PER = 50us

PKGREF = Vs

VOFF = 0V

VAMPL = 10V

FREQ = 20k

20V

lab-1a

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