Additional Magneto Motive Force of Spoke-Type Vernier Permanent-Magnet Machines

The traditional permanent magnet (PM) magneto motive force (MMF)/specific permeance model has been widely applied to analytically predict the magnetic field of Vernier permanent-magnet machines (VPMs). However, it fails to accurately predict the performances of spoke-type VPMs. This article clarifies the intrinsic reason, i.e., the spoke-type VPMs have a large additional PM MMF introduced by the stator slotting, while the traditional model ignores it. In this article, the additional PM MMF is analytically calculated and its influence on electromagnetic performance is comprehensively investigated. It shows that the additional PM MMF leads to reductions in the airgap flux density, back electromotive force (EMF), and torque performances of spoke-type VPMs. Especially when the pole ratio is high, the reductions due to the additional PM MMF are more obvious. Finally, a spoke-type VPM prototype is built and tested to verify the theoretical analysis.