An Interior Permanent Magnet Synchronous Machine with Asymmetric Structure for Improving Torque Density

There is a 45° difference in the current angle between the peak of the reluctance torque and permanent magnet (PM) torque in conventional Interior PM synchronous machine (IPMSM), which makes it impossible to achieve the maximum simultaneously, and can further increase electromagnetic torque. This article proposes a novel design method and topology structure for IPMSM with asymmetric structure, utilizing magnetic field shifting (MFS) to improve performance such as torque density and torque ripple. Firstly, the torque enhancement principle of this method was theoretically analyzed under different reference frames, and the relationship between the structure and MFS was studied. Taking the evolution process from the structural prototype to the innermost layer of the novel structure as an example, the design ideas and structural characteristics of the proposed method are explained. And it is verified using magnetic field distribution by finite element analysis (FEA). The conventional IPMSM is modified by the proposed design method to verify its effectiveness. Even if the proposed asymmetric structure is not used to improve the uneven saturation of IPMSM, the average torque, torque ripple, torque-current angle characteristic, and torque-current characteristic of IPMSM improved by the proposed method are still all improved.