Investigation of Unbalanced Magnetic Force in Permanent Magnet Synchronous Machines With Asymmetric Design

This paper aims to disclose the unbalanced magnetic force (UMF) and the degenerated vibration and noise performance, which are possibly caused by some asymmetric designs in permanent magnet synchronous machines (PMSMs). These designs were all previously proposed to reduce cogging torque or torque ripple, but their negative effects were paid less attention. Various PMSMs are designed and simulated to verify the asymmetric design methods and the generation of UMF. It is found that improving the torque characteristic is generally at the expense of increasing the detrimental effect of local force. Experimental tests on a prototype indicate that the vibration and noise performance largely deteriorates with an asymmetric design at relatively high speed. Based on the work, it is recommended to improve the torque characteristic using the symmetric design methods instead, and the asymmetric design can be marginally accepted under low-speed or light-load condition, from the perspective of vibration and noise performance.