Optimal design of a cost-effective SPM motor to suppress torque pulsations using multi-grade permanent magnets

This paper presents an optimal design for a surface-mounted permanent magnet motor (SPMM) to save magnet cost and suppress torque pulsations, by using multi-grade permanent magnets. Based on a conventional SPMM with NdFeB magnets, the proposed SPMM is designed with multi-grade ferrite and NdFeB magnets, and then optimized by combing the Kriging method with a genetic algorithm, for further minimizing torque pulsations and saving the magnet cost. As a result, the cogging torque, torque ripple, and magnet cost of the optimized SPMM are highly reduced compared to the conventional SPMM. The optimized SPMM is finally verified to have good endurance against the irreversible demagnetization within three times of the rated current excitation, with the aid of a finite element method.