Acoustic Noise and Vibration of an Interior Permanent Magnet Traction Motor: PWM Effect

The pulse width modulation (PWM) fed permanent magnet motor drives have been widely applied in various applications. Plenty of work has been carried out to investigate the effect of PWM on motor losses and efficiency. In this paper, the focus is to study the impact of PWM on the acoustic noise and vibration performance of a 48-slot 8-pole interior permanent magnet (IPM) machine. The current and radial force harmonics generated due to the PWM effect are identified and the contributions to acoustic noise of the motor are outlined. Results show that the PWM effect on the acoustic noise levels for this motor are negligible since the total sound pressure levels (SPLs) are very similar for sinusoidal and PWM currents for base- and maximum-speed operations. However, the effect on acoustic noise can be significant if introduced PWM harmonics overlap with the stator's natural frequencies to cause resonance, which should be carefully considered during the design process.