Optimal pulsewidth modulation for AC servos and low-cost industrial drives

Abstract

An optimal pulsewidth modulation method for inverters is described in which the durations of switching subcycles are considered as optimization variables, a subcycle being the time sequence of three consecutive switching state vectors. Operation at variable subcycle duration entails a prediction of the controlling reference voltage vector. It is a special advantage that the optimization and prediction can be carried out off line. The optimal technique exhibits high dynamic performance. It can be used for synchronized and asynchronous modulation in a wide range of switching frequencies. The optimization reduces the harmonic currents at a given switching frequency. The Fourier spectrum lacks dominant carrier frequencies. Hardware implementation cost compares with existing nonoptimal modulation methods.