Design and Optimization of a Brushless Wound-Rotor Vernier Machine

In this paper, a permanent magnet (PM)-less, brushless, wound-rotor vernier machine (BL-WRVM) is proposed for variable speed applications such as electric vehicles and washing machines. The wound rotor is excited through an already existing brushless topology, which requires a dual inverter configuration to generate an additional subharmonic component in the stator magnetomotive force (MMF). Different from permanent magnet vernier machines (PMVMs), the proposed BL-WRVM provides easy regulation of the rotor flux for variable speed operation. A 24-slot, 4-pole stator, and 44-pole outer rotor were designed, and 2D finite element analysis (FEA) was carried out to determine the performance of the proposed machine. To improve the performance of the proposed machine, optimization of the rotor and stator winding turns was done. The optimized model was further analyzed for wide-speed operation, and its performance was then compared with that of an equivalent permanent magnet vernier machine (PMVM). The proposed machine has the advantage of low cost due to its PM-less structure and is suitable for variable speed applications.