Research on cogging torque weakening of direct-drive permanent magnet motor with inner enhance force

This paper proposes a simple and efficient method to weaken the cogging torque of the direct-drive permanent magnet motor with inner enhance force (IEF-DDPMM). It is characterized by adjusting the relative position of the inner and outer permanent magnets so that the cogging torque generated by the inner and outer air-gaps is opposite in phase, thus eliminating or weakening a certain order of cogging torque. For IEF-DDPMM, the expression of cogging torque and the variation law of cogging torque with the staggered-pole angle are derived by the analytical method. The relationship between optimal staggered-pole angle and the pole-slot combination is analyzed. The influence of staggered-pole on average torque and torque ripple is analyzed. Finally, the commercial finite element software ANASYS-Maxwell is used for simulation, and the simulation results are consistent with the analytical results. The results show that the cogging torque of IEF-DDPMM is the linear superposition of cogging torque from inner and outer parts; choosing a suitable staggered-pole angle can effectively weaken the cogging torque and reduce the torque ripple. Besides, the average torque reduction caused by the staggered-pole method can be compensated by adopting the internal power factor angle compensation strategy. (c) 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.