Review on Power Factor Improvement of Vernier Machines

Vernier machines (VMs) operate on the principle of magnetic field modulation and exhibit high torque density. However, their low power factor (PF) restricts broader applications. This paper provides a thorough review that focuses on the PF improvement of VMs. This review introduces the mechanism and influencing elements of the PF, as well as the optimal design schemes for PF from three perspectives: the excitation source, the modulator, and the filter. Additionally, this paper analyzes the optimization principles of these schemes based on magnetic field modulation theory. Moreover, advancements in machine control and the utilization of advanced materials for optimizing PF are discussed. This paper observes relevant technologies, provides a roadmap, and inspire future research direction for solving the PF problem of VMs.