| Summary: | Owing to the high speed of the interior permanent magnet synchronous motor (IPMSM), the high-frequency howling noise of electromagnetic vibration is disruptive to passengers. The harmonics of the electromagnetic force serve as the primary source of vibration noise. In this work, a non-uniform air gap with a microgroove surface of the motor was proposed for optimizing the harmonics of the electromagnetic force. The research was based on a developing project of a 150 kW IPMSM for a battery electric vehicle (BEV). To find the optimal microgroove surface of the rotor, six variables were defined for the microgrooves through 9900 calculations using the Ansys Workbench. By finite element analysis (FEA) comparisons, the non-uniform air gap with microgroove surface significantly reduced the no-load back Electromotive Force (EMF) harmonics, the total distortion rate (THD) from 2.57% to 1.52%, and the torque ripple from 10.84% to 4.06%. A motor prototype with a non-uniform air gap was manufactured to prove the accuracy of the simulation. Under the whole open throttle (WOT) condition, the vibration acceleration of the 24th and 48th order was approximately 10 dB lower than the target vibration noise limit.
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