Design Considerations of Spoke-Array PM Vernier Machine for Different Power Levels

Spoke-Array permanent magnet vernier machine (SA-PMVM) is a competitive candidate for direct-drive applications owing to its high torque density, while neither the theoretical models nor relations between parameters and performances are well established due to the complex influence of flux barrier effects, which further lead to the lack of design guidance for SA-PMVMs. This paper is devoted to propose a comprehensive analysis and design of SA-PMVMs covering different power levels. Via constructing closed-form per-unit formulations, the cross-coupling influences of pole ratios, i.e., the pole-pair ratios of PM to armature winding, stator slot numbers, and other normalized geometric variables, including stator slot opening ratios, length-radius ratios, et al., on machine performances are revealed. Then, the optimal selections of pole ratios as well as critical geometric parameters to satisfy various technical indexes, such as torque density and power factor, are determined. Based on the proposed design approach, two design examples with different slot/pole combinations are built and compared. Meanwhile, a prototype with 18-stator-slot 13-rotor-pole-pair is manufactured and tested to verify the feasibility.