Design of a Novel Parallel-Hybrid-Excited Vernier Reluctance Machine with Improved Utilization of Redundant Winding Harmonics

DC-excited Vernier reluctance machines (DC-VRM) have attracted much attention due to their wide speed range and robust rotor configuration. However, DC-VRM suffers from low torque density and low efficiency, which restricts their potential in high-performance driving applications. To solve this problem, this paper proposes a novel parallel-hybrid-excited VRM with improved torque density and enhanced bidirectional field regulation capacity. The key is introducing an auxiliary stator-slot PM excitation to utilize redundant airgap harmonics of a single-layer concentrated armature excitation, thus boosting the torque density. Meanwhile, this auxiliary stator-slot PM excitation produces a parallel flux return path with dc field excitation and two excitation sources interact with different winding harmonics, which can provide an effective bidirectional field regulation. The machine structure, operation principle, and harmonic analysis are introduced first. Then, the feasibility of the proposed topology with both ac and dc electrical ports is evaluated by using finite-element method. Further, a design optimization and comparative study is performed between the proposed design and other existing topologies in terms of their torque density, overload ability, core loss, and efficiency. Finally, a prototype is manufactured. Relevant tested results agree well with the finite-element predications.