Sinusoidal Pulse-Width Modulation
• In multiple-pulse modulation, all pulses are
the same width
• Vary the pulse width according to the
amplitude of a sine wave evaluated at the
center of the same pulse
ECE 442 Power Electronics
1
Generate the gating signal
2 Reference Signals, vr, -vr
ECE 442 Power Electronics
2
Comparing the carrier and reference signals
• Generate g1 signal by comparison with vr
• Generate g4 signal by comparison with -vr
ECE 442 Power Electronics
3
Comparing the carrier and reference signals
ECE 442 Power Electronics
4
Potential problem if Q1 and Q4 try to turn ON
at the same time!
ECE 442 Power Electronics
5
If we prevent the problem
Output voltage is low when g1 and g4 are
both high
ECE 442 Power Electronics
6
This composite signal is difficult to generate
ECE 442 Power Electronics
7
Generate the same gate pulses with one
sine wave
ECE 442 Power Electronics
8
Alternate scheme
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rms output voltage
• Depends on the modulation index, M
V V
o
p
S

V



2p
m
S
m 1
Where δm is the width of the mth pulse
ECE 442 Power Electronics
10
Fourier coefficients of the output voltage

4V
n 
3
B 
sin
sin n  
n
4 
4
n  1, 3, 5,..
2p
S
n
m 1
m
m
m



 
 sin n    

ECE 442 Power Electronics
m
m
4 
11
Harmonic Profile
ECE 442 Power Electronics
12
Compare with multiple-pulse case for p=5
Distortion Factor is considerably less
ECE 442 Power Electronics
13