PM-Bottom-Arc Shaping Method in Surface-Mounted PM Machine for Improved Torque Profile and Reluctance Torque

This paper proposed a PM-bottom-arc shaping rotor for high-speed SPM machine. The PM-bottom-arc shaping rotor can offer three advantages. First, the third magnetic harmonic is utilized for fundamental flux density enhancement, and the additional reluctance torque can also be introduced by the PM-bottom-arc shaping method. Both of them help to increase average torque output. Second, the high-order harmonics can be effective suppressed to obtain low torque ripple. Third, the outer profile of the PM-bottom-arc shaping rotor are smooth, which overcomes the conventionally existing stress concentration of the PM-top-arc shaping methods, especially for high-speed operation. Firstly, the PM-bottom-arc shaping concept and its electromagnetic characteristics are presented and compared with conventional PM-top-arc shaping method. Then, the PM-bottom-arc model is established, and the optimal third-harmonic injection factor is derived to obtain the highest torque output. Following that, various electromagnetic performances of the proposed rotor are compared with those of the conventional PM-top-arc shaping and typical curve-shaped designs. Finally, a research prototype is developed and several dynamic/steady test-rigs are constructed for the experimental validation. The simulation results demonstrate that the proposed PM-bottom-arc shaping machine exhibits 11.1% higher average torque than the conventional third-harmonic shaping design, while its torque ripple remains similar to that of the third-harmonic PM-top-arc shaping design, i.e., 35.5% torque ripple of the commonly used curve-shaped design.