Torque Improvement of a Hybrid-Excited Vernier Reluctance Machine with High-order-harmonic Winding Design for Electric Vehicle Application

Hybrid-excited Vernier reluctance machine (HEVRM) with dc field excitation and sub-slot bottom PMs is attractive for electric vehicle (EV) application in electrification transportation due to its high torque density and excellent flux regulation capability. To further enhance the torque density, a novel high-order harmonic winding design (HHWD) method is proposed. The key is to break the previous winding design principle using the fundamental field excitation harmonic, but to propose a novel winding design principle with flux modulation effect in which high-order field excitation harmonic is utilized instead. In this way, the no-load back-EMF and steady torque can be enhanced by 174% and 142%, comparing with the previous counterpart. In this paper, the machine structure and operation principle are introduced in detail, which mainly focuses on the comparison between fundamental-harmonic winding design (FHWD) and HHWD on the dc field excitation harmonic utilization condition. Using the finite element analysis (FEA), the electromagnetic performance comparisons of HEVRMs with FHWD and HHWD are conducted. Finally, the prototype of HEVRM with HHWD is manufactured and tested, which verifies the correctness of FEA results.