Design and Optimization of an Outer-Rotor SPMSM with permanent magnets of Reverse Step Shape

Cogging torque and torque ripple of permanent magnet synchronous motor is one of the main concerns in design. And weakening harmonics of air-gap flux density and back electromotive force is a significant way to reduce cogging torque and torque ripple. In this paper, an outer-rotor surface-mounted permanent magnet synchronous motor (SPMSM) with permanent magnets of reverse step shape (SPMSM-RS) is designed and optimized. Compared with conventional SPMSM (CSPMSM) and that with permanent magnets of step shape (SPMSM-S), the motor of this model has fewer harmonics of air-gap flux density and fewer leakage fluxes by 2-D finite-element analysis method. Finally, the proposal model is optimized by genetic algorithm, with respectively minimum total harmonics distortion (THD) of no-load back electromotive force (EMF) and minimum torque ripple on rated operation as objective functions. The result shows that the model by optimizing no-load back EMF has a good performance with fewer harmonics of back electromotive force. And the model by optimizing torque ripple has a good performance with fewer torque ripple.