Optimal Design of a Surface-mounted Permanent Magnet Motor with Multi-grade Ferrite Magnets to Reduce Cogging Torque and Torque Ripple

This paper deals with the optimal design of a surface-mounted permanent magnet motor (SPMM) to reduce cogging torque and torque ripple by using multi-grade ferrite magnets. Based on a conventional SPMM with single-grade ferrite magnets, the proposed SPMM is designed with four-grade ferrite magnets, and optimized to obtain low cogging torque and torque ripple by maintaining the required torque, utilizing the Kriging method and a genetic algorithm. The results obtained by the finite element analysis show that the optimized SPMM with multi-grade ferrite magnets has highly reduced cogging torque and torque ripple by maintaining the similar average torque, as compared to the conventional SPMM. Furthermore, the analysis of the working points for the multi-grade ferrite magnets reveals that the optimized SPMM has good durability against the magnet demagnetization