Review on Power Factor Improvement of Vernier Machines

Due to flux modulation (FM) effect, vernier machines (VMs) achieve high torque density, marking them as promising for variable speed applications. However, their practical implementation is hindered by the challenge of a low power factor (PF), which leads to the poor generation power quality, the increased converter capacity, and the limited overload capability. This paper offers a comprehensive review, summarizing relevant emerging technologies aimed at breaking through the limitation. It delves into the mechanisms, calculation methods, and optimal design strategies for PF from three core angles: the excitation source, the modulator, and the filter. By examining these pertinent technologies, the main findings reveal that optimizing the three elements can reduce leakage flux and enhance the working harmonic ratio of VMs, thereby improving the PF of VMs. By examining pertinent technologies, this paper outlines a strategic roadmap and aims to spark future research endeavors to overcome the PF challenge in VMs.