Analysis of the Air-Gap Flux Density Components Contributing to the Torque in a Surface Permanent Magnet-type Vernier Motor

The air-gap magnetic flux density in a surface permanent magnet-type vernier motor, which generates high torque at low speeds, is analyzed using a mathematical model that incorporates the armature-winding magnetomotive force (MMF) harmonics and air-gap permeance pulsations, and a torque analytical method is subsequently proposed. The specific components producing the torque are identified by evaluating the local torque produced by the spatial harmonic flux density acting on the exciting coils (equivalent to permanent magnets). The results suggest that the low-speed operation of the rotor is driven by the synchronous torque generated by these spatial harmonics. Moreover, a high torque is generated by amplifying the spatial harmonic flux density via superimposing the slot harmonics on the armature MMF harmonics. Finally, the proposed torque analytical method and theoretical reasoning are validated through finite element method analysis and experimental testing using a prototype.