Effect of uneven magnetization on magnetic noise and vibrations in PMSM – application to EV HEV electric motor NVH

This paper studies the effect of uneven pole magnetization on acoustic noise and vibrations radiated by Permanent Magnet Synchronous Machines (PMSM) under Maxwell force excitations in open-circuit condition and on the full speed range. First, the effect of magnetic asymmetries is analyzed using analytic equations based on permeance / magneto motive force. Then, electromagnetic, structural and acoustic calculations are performed using MANATEE software on a 48s8p Interior PMSM used in Electric Vehicle (EV) / Hybrid Electric Vehicle (HEV) automotive applications. To speed up calculations under asymmetrical conditions due to magnetization variations, Electromagnetic Vibration Synthesis algorithm is used. Simulation results show that uneven pole magnetization significantly affects airborne noise and vibrations, inducing low frequency noise and new resonances with structural modes which are not predicted by the Greatest Common Divider (GCD) rule on pole/slot combination.