A new hybrid random pulse width modulator for industrial drives

A new hybrid pulse width modulator (HPWM) is suggested. It provides (a) extended linearity (up to modulation index of 1.154), (b) reduced switching losses, and (c) less annoying acoustic noise by changing the current spectrum. The spectrum is modified by changing randomly the ratio of the durations of the application of the two zero-state vectors, V/sub 0/ and V/sub 7/. Such a way to modify the current spectrum is effective at modulation indices up to m/spl les/0.8. A new method that provides additional capability of controlling the spectrum for m>0.8, and thus the emitted acoustic noise from the drive, is proposed and investigated. The method extends the HPWM with an additional algorithm which randomly selects the PWM carrier frequency as either f/sub carr/ or 2/spl middot/f/sub carr/. The extra losses, which normally result in an increase of the average switching frequency, are avoided by dropping one of the zero-vector states for m>0.8. This corresponds to using a discontinuous modulation function. The transition between the different operation modes is seamless and the method is easy to implement due to the HPWM structure. Simulation results and experiments validate the usefulness of the method proposed.