Harmonic analysis of nondeterministic switching methods for DC-DC power converters

The authors present a rigorous theoretical harmonic analysis of random pulse width modulation (RPWM) method and random pulse position modulation (RPPM) method for dc-dc converters. The theoretical relationships of discrete harmonics, continuous noise and output voltage ripple of the RPWM and RPPM schemes are established and compared with those of a standard deterministic PWM scheme in a buck converter. Limitations in the randomly switched dc-dc converters are highlighted. The theoretical predictions indicate that the randomized schemes generally have an inherent problem in achieving low output voltage ripple due to the low-frequency continuous noise within the pass-band of the converter filter. For dc-dc power conversion, the RPPM method offers much better output voltage performance than the RPWM method.