Design of Axial-Flux Permanent Magnet Motors With High Torque Density and Low Thermal Raise for Electric Motorcycle
You Zhou, Junyao Liu, Zhi Chen, Guanghui Yang, Yaojie He, An Li, Ning Kang, Jiahao Chen, Christopher H. T. Lee
Abstract
Axial-flux permanent magnet synchronous motor (AFPMSM) is a compact and high-torque solution for direct-drive e-bikes. However, its complex 3-D flux path and thermal management challenges hinder its efficiency. To address these issues, an AFPMSM with Halbach PM array (H-AFPMSM) is proposed. Leveraging self-shielding magnetization, the H-AFPMSM demonstrates higher magnetic loading and significantly reduces heat dissipation while maintaining torque density. The performance of the AFPMSM is first analyzed to guide topology selection and a rapid three-stage optimization method is proposed thereby. Comparative analysis with surface-mounted PM AFPMSM (S-AFPMSM) and radial-flux PMSM (RFPMSM) via finite element analysis and 5-kW full-loading prototype testing shows a 30% increase in torque density for H-AFPMSM compared to RFPMSM and a 40°C decrease in coil temperatures compared to S-AFPMSM due to 25% loss reduction. Moreover, the proposed H-AFPMSM exhibits a 5%∼10% improvement in efficiency across the entire operating speed range compared to S-AFPMSM. Via rapid simulation and performance enhancement techniques, the H-AFPMSM is developed as an ideal fit for e-bike scenario.