Current Harmonics Impact on Torque Ripple in PM Machine Drive System

The current of an electric machine driven by PWM switching inverter is not ideal sinusoidal, containing different levels of harmonics. The current harmonics have important impact on the electrical machine torque ripple which could translate into transmission and vehicle level Noise Vibration and Harshness (NVH). In this work, the current waveforms were measured from dyno test at prescribed torque and speed levels, and the electric machine torque ripple was computed with the measured current. This paper will focus on the investigation of the current harmonics behaviors and features at various torque and speed conditions, the impact on torque ripple, and the possible mitigation method to reduce torque ripple. The key findings and insights include: the current harmonics for the same torque conditions but in different motoring and regenerating conditions could have impact on torque ripple in the opposite direction; The phase angle of current harmonics tend to be more sensitive in driving the torque ripple level in comparison to the magnitude of current harmonics; the torque ripple can be lowered with appropriate values of current magnitude and phase angle compared to pure the sinusoidal-waveform current.