Continuous PWM Strategies of Multi-Phase Inverter-Fed AC Drives

Abstract

Different continuous PWM strategies of multi-phase inverter-fed ac motors are investigated from the point of view of ac motor harmonic losses. It is shown that for phase number over seven - in comparison with the space vector or with the harmonic injection methods - the natural or regular sinusoidal PWM of multi-phase system gives the best solution both from the point of view of the simplicity of realization and the value of harmonic losses. However, the stator harmonic current losses are slightly higher while the rotor harmonic current losses considerably lower than those of the three-phase system. The theoretically derived expressions for stator and rotor loss (for infinite value of switching frequency (MATHCAD program) are checked with resulting of direct computation for finite value of switching frequency (MATLAB program) and by simulation.