A COMPARISON OF NONDETERMINISTIC AND DETERMINISTIC SWITCHING METHODS FOR DC-DC POWER CONVERTERS

An analysis and experimental results of the random pulsewidth modulati on (RPWM) and random pulse-position modulation (RPPM) methods for de-d e converters are presented. The characteristics and performance of pow er converters under two randomized modulations are evaluated. The theo retical relationships of discrete harmonics, continuous noise, and out put-voltage ripple of the RPWM and RPPM schemes are established and co mpared with those of a standard deterministic pulsewidth modulation (P WM) scheme in a buck converter. Limitations in the randomly switched d e-de converters, which have not been addressed before? are highlighted . Randomized schemes generally have inherent problems in achieving low -output-voltage ripple due to the low-frequency continuous noise withi n the passband of the converter filter. The inherent low-frequency noi se-induced voltage ripple problems of nondeterministic switching metho ds for de converters are confirmed experimentally. The performance of the RPPM method is found to be closer to the standard PWM method than that of the RPWM method. For de-de power conversion, the RPPM method o ffers much better output-voltage performance than the RPWM method.