Comparative Analysis of Vernier Machines with Spoke, Surface Mounted, and Halbach PM Rotors for In-wheel Traction

Axial-flux Permanent Magnet (AFPM) machines are well-suited for in-wheel traction in electric vehicles due to their compact structure and higher torque density. This paper presents a large-scale design optimization of an axial-flux permanent magnet vernier machine (PMVM) of the MAGNUS type with a double stator configuration. The active stator features double-layer wound coils, while the passive stator is unwound but has a similar profile. The reference design employs a rotor with permanent magnets (PMs) arranged in a spoke-type field-intensifying pattern, providing high flux concentration. Design optimization was performed using 3-D electromagnetic Finite Element Analysis (FEA) and the Differential Evolution (DE) algorithm. A best design from the Pareto front was selected, and a comparative study was conducted by replacing the spoke-type rotor with a Halbach array and a surface-mounted PM (SPM) rotor. The performance of the machine, considering these proposed rotor types was assessed for traction requirements. The results indicate that the spoke configuration is superior in terms of power density, efficiency, cost of active material, and having a higher constant power region.