Analysis of the impact of pulse-width modulated inverter voltage waveforms on AC induction motors

Abstract

The purpose of this paper is not to reveal any new technology or major breakthrough pertaining to the impact of pulse-width modulated (PWM) adjustable speed drives operating on AC motors. Nor is it to discuss the merits of the various designs of the drives. The applications are also well defined. The area where much confusion still exists deals with the voltage waveform impact on the motor performance, hence, this is the central theme of the paper. The author has assumed that the traditional fundamental sine-wave voltage is (except for starting or outside influences) a steady-state condition, with a maximum and an RMS value, whereas the voltage waveform supplied by a PWM drive can have significant harmonics and transients which may alter the motor performance characteristics and life expectancy. The effects of the maximum voltage, rate of rise, switching frequencies, capacitors, resonance, and harmonics are all considered.