Air-Gap Flux Density Characteristics Comparison and Analysis of Permanent Magnet Vernier Machines With Different Rotor Topologies

In this paper, the air-gap flux density characteristics of three permanent-magnet vernier machines (PMVMs) with different rotor-PM topologies, i.e., surface, Halbach and spoke-array types are analyzed and compared. The investigated machines share the same stator configuration characterized by fractional-slot concentrated windings and multitooth split-pole structure. By using the finite-element analysis, the dominant factors that influence the air-gap flux density characteristics of the proposed PMVMs are investigated and discussed. It demonstrates that the air-gap flux densities of all these machines are predominantly sensitive to conventional parameters, such as air-gap lengths, PM thicknesses, as well as exclusive parameters of the flux modulation pole (FMP) width and gear ratio. The higher pole arc coefficients are desired for PMVMs with surface and Halbach PMs, whereas a small value is preferred for poke-array PMVM. In addition, higher air-gap flux density can be obtained for all three PMSMs with suitable FMP width and optimal gear ratio. Finally, the aforementioned analysis and calculation are verified by one PMVM prototype with spoke-array PM configuration.