Analysis of air-gap field modulation effect on torque contribution of 6-slot 4-pole high-speed permanent magnet machine

PurposeThis paper aims to investigate and analyze the air-gap field modulation (AGFM) effect on torque contribution in a 6-slot/4-pole high-speed permanent magnet (HSPM) machine. To further illustrate the torque generation mechanism, the torque contribution is quantified using the Maxwell stress tensor (MST) method.Design/methodology/approachFirst, a simplified permanent magnet (PM) magnetomotive force model is established to identify the effective main-order working field harmonics. Then, the MST method is used to determine the average torque contributions of the effective main-order working field harmonics. Finally, the influences of various stator and rotor parameters on the AGFM effect are analyzed and optimized to enhance the torque density.FindingsApart from the fundamental harmonics, the AGFM harmonics contribute non-negligible average torque on the HSPM machine, and the optimized machine has higher torque density. Finally, a prototype of the 10 kW HSPM machine is manufactured and experimented with to validate the effectiveness of the theoretical analysis.Originality/valueIn this paper, the torque generation mechanism of the HSPM machine is investigated and analyzed. Meanwhile, the AGFM effect of the HSPM machine with different design parameters is analyzed and optimized to enhance the torque density.