Investigation of a Novel Dual-Side PM Vernier Machine With Two-Slot-Pitch Coils

Permanent magnet vernier (PMV) machines exhibit high torque density but low power factor. Selecting low pole ratios (PRs) and adopting two-slot-pitch coils have been proven to be efficient in enlarging the power factor of the PMV machines. However, the low PR results in lower torque density. Moreover, due to the different winding configurations of the two-slot-pitch coils, only some of which can denote high power factors. To improve the torque density and power factor simultaneously, outer-rotor dual-side PMV (DPMV) machines adopting two-slot-pitch coils and relatively low PR are introduced in this article. Moreover, the comparative analysis of torque production mechanisms of DPMV machines adopting different two-slot-pitch coils is presented. Since the stator-permanent magnet (PM) arrangements of the compared DPMV machines are different due to the different winding pole numbers, the electromagnetic characteristics are distinct. First, the PM-MMF-permeance-based analytical model is built to analyze the bidirectional flux modulation effects and reveal the sources of working air-gap flux field harmonics of the investigated DPMV machines. The key performances of the DPMV machines with different winding configurations and PRs are investigated and compared. It indicates that when the stator-PMs are arranged to be a PM-core–PM-core sequence, the DPMV machines with two-slot-pitch coils can achieve significantly improved torque density and power factor. Finally, an 18-stator-slot/13-pole-pair DPMV prototype is tested, and the measured results indicate that the proposed DPMV prototype has a torque density of up to 18.0 N·m/L and a power factor of 0.93.