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Power Electronics for Energy System (EET424)
Laboratory Module
EXPERIMENT 6
Pulse Width Modulation (PWM) Circuits for Inverters (Part 2)
Another method that we are going to learn in this experiment is the single-pulse width
modulation technique. This method is much easier to be made and the circuit is less
complex compares to the sinusoidal PWM technique. The modulated wave is a squarewave of low frequency (may be 50Hz or 60Hz) and envelopes the high frequency
switching pulses. The effective power to the load can be controlled by varying the duty
cycle of the high frequency pulses. Fig 2.0 below shows the block concept of producing
the output waveform.
Fig 2.0 : Single- PWM concept
1) Open a new document on the PSIM. Draw the circuit as shown in Fig 2.1 below.
Fig 2.1 : Single-PWM circuit
2) Set the parameters of VSQ1 as :
UNIVERSITI MALAYSIA PERLIS – Exp.6 (Revision 2)
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Power Electronics for Energy System (EET424)
Laboratory Module
Name : VSQ1
Vpeak_peak : 5
Frequency : 50
Duty Cycle : 0.5
DC Offset : 0
3) Similarly, set the parameters of VSQ2 as :
Name : VSQ2
Vpeak_peak : 2
Frequency :1k
Duty Cycle : 0.5
DC Offset : 0
4) After you have completed the circuit, set the simulation control time to : Time step
is 10m and Total time is 0.03.
5) Run the program. Then click Simview to observe the respective waveforms. Inside the
Data Selection box, click VSQ1 and VSQ2 together and press Add. Then press OK
and both of the waveforms will appear on the screen.
6) Then click the Add Screen button at the top menu and another selection will be
displayed. Now choose Vs1,s2 and Vs3,s4 together and press Add. A new screen
with the waveforms should appear.
7) Neatly draw all of the waveforms on a graph paper and clearly labels them.
(5x2m)
8) Save the schematic circuit into your pen-drive. You will need to copy the circuit into
your next week’s lab.
9) The effective power to the load can be controlled by varying the duty cycle of the
switching frequency. Design a simple circuit using PSIM to give a single output of
pulses that the width can be controlled accordingly. Then simulate it to prove that
your circuit works well. (Hint : refer to certain section of the circuit in Fig 1.1 (Exp.5)
and use DC voltage source). Draw your designed circuit.
(5m)
10) Run your circuit and draw the related waveforms to show the output pulses width
changes as you use 5 different DC voltage levels (at 0.3V, 1.5V, 4.0V, 6.5V and
7.0V). (Draw the output pulse for each condition between 10ms – 13ms).
(4x5m)
11) Determine the width of each pulse (in ms) at different DC voltage levels (VDC1) and
fill in as in the table below.
VDC1
0.3V
1.5V
4.0V
6.5V
7.0V
Pulse width (ms)
(5m)
UNIVERSITI MALAYSIA PERLIS – Exp.6 (Revision 2)
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Power Electronics for Energy System (EET424)
Laboratory Module
12) Plot a graph of Pulse width agaist VDC1.
(4m)
13) From the graph, determine the VDC1 that needs to produce a pulse width
output of 0.8ms.
(2m)
14) Change VDC1 to 8.0V and observe the output. Is it zero or not ? Please explain
why the condition is as such.
(2+3m)
15) What is the actual limit voltage that VDC1 needs to be set in order to get the
output to be zero ?
16) Please state your conclusion for the whole of this experiment.
(2m)
(3m)
(Total=56m)
UNIVERSITI MALAYSIA PERLIS – Exp.6 (Revision 2)
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