Pulse-Width Modulation PSpice Simulation
Pulse-width modulation is used to provide a 60-Hz voltage across a series RL load
with R 1 and L 2.65 mH. The dc supply voltage is 100 V. The amplitude of
the 60-Hz voltage is to be 90 V, requiring ma 0.9. Use PSpice to obtain the current
waveform in the load and the THD of the current waveform in the load. Use (a) bipolar
PWM with mf 21, (b) bipolar PWM with mf 41, and (c) unipolar PWM with
mf 10.
■ Solution
(a) The PSpice circuit for bipolar PWM (Fig. 8-25b) is run with ma 0.9 and mf 21.
The voltage across the load and the current in the load resistor are shown in
Fig. 8-27a. The currents for the 60-Hz fundamental and the lowest-order harmonics
are obtained from the Fourier option under x axis in Probe. The harmonic amplitudes
correspond to the peaks, and the cursor option determines precise values. The rms
current can be obtained from Probe by entering the expression RMS(I(R)). The
total harmonic distortion based on the truncated Fourier series is computed from
Eq. (8-17). Results are in the table in this example.
(b) The PSpice circuit is modified for mf 41. The voltage and current waveforms are
shown in Fig. 8-27b. The resulting harmonic currents are obtained from the Fourier
option in Probe.
EXAMPLE 8-11
Figure 8-