a voltage-controlled voltage source ETABLE. Both methods compare a sine
wave to a triangular wave. Either method allows the behavior of a specific load
to a PWM input to be investigated.
If the load contains an inductance and/or capacitance, there will be an initial
transient in the load current. Since the steady-state load current is usually of interest,
one or more periods of the load current must be allowed to run before meaningful
output is obtained. One way to achieve this in PSpice is to delay output in the transient
command, and another way is to restrict the data to steady-state results in
Probe. The reference signal is synchronized with the carrier signal as in Fig. 8-17a.
When the triangular carrier voltage has negative slope going through zero, the sinusoidal
reference voltage must have positive slope going through zero. The triangular
waveform starts at the positive peak with negative slope. The phase angle of the
reference sinusoid is adjusted to make the zero crossing correspond to that of the triangular
wave by using a phase angle of 90/mf. The following example illustrates
a PSpice simulation of a bipolar PWM application.
EXAMPLE 8-