Analysis and Reduction Methods of Cogging Torque in Dual PM Vernier Machines with Unevenly Distributed Split Teeth

This article investigates the source and reduction methods of cogging torque in dual PM Vernier machines (DPVMs), especially for the ones with unevenly distributed split teeth (UDST). At first, the increase of no-load back electromotive force in DPVMs with UDST is illustrated through the analysis of airgap working flux harmonics. The reason for largely increased cogging torque of DPVMs with UDST is then analyzed, and main flux harmonics that contribute to cogging torque are identified. To reduce cogging torque and torque ripple, several effective methods are introduced in this article, which are mainly based on the reduction or offset of corresponding airgap flux harmonics. The cogging torque reduction effects and torque performances of these methods are compared. Among them, newly proposed N/S-parts offset method is proved to be superior to other methods in DPVMs. A new DPVM prototype with UDST and N/S-parts offset structure is built and tested. Experimental results show that through the N/S-parts offset method, cogging torque of the machine is largely decreased from 9 to 0.3 N·m, which validates the analysis and simulation results.