No-load power losses and motor overheating effects versus PWM switching frequencies

Electric motors driven by pulse-width modulated (PWM) waveforms exhibit different power loss and heating characteristics than line-fed motors. Experimental results indicate that motor losses and heating increase as the drive switching frequency decreases. Motor power losses for low switching frequencies are described, and if the increase in motor power loss is high enough such that motor overheating is a concern, a three-phase line reactor between the drive output and the motor terminals may be used to mitigate the additional motor losses and possible motor overheating. This paper presents the effect of PWM waveforms on motor losses and demonstrates that the use of a small three-phase line reactor between the drive and the motor dramatically reduces the motor losses under low PWM switching frequencies.