Low Pole-Pair Ratio Integration Design of Permanent Magnet Vernier Machine With Improved Power Factor

Benefited from flux modulation effects, permanent magnet Vernier machines (PMVMs) have the advantage of high torque. Generally, the higher pole-pair ratio (PR), i.e., PM pole-pair to armature winding pole-pair, the stronger flux modulation effects, as well as the higher torque. However, PMVMs with high PR suffer from low power factor due to the parasitic large inductance. This article is devoted to propose a low PR integration design approach of PMVMs to achieve the high average torque and power factor simultaneously. According to exploit multiple working harmonics with low PRs, not only the high power factor and low inductance characteristic can be maintained, but also the average torque and flux modulation effects can be strengthened. Further, the stator flux barrier has been added to restrict the parasitic no-working harmonics with high PRs. Based on these, two PMVM design examples with different slot/pole combinations are constructed and analyzed to verify the effectiveness of the proposed design approach. Finally, a prototype is manufactured and experimented. It is showed that under electric loading 320 A/cm, the active volume torque density of proposed PMVM can be up to 33.4 N·m/L, which is comparable to regular PMVM with high PR 8, while power factor can be improved from 0.63 to 0.8.