Inner Rotor Shaping Method for Torque Ripple Suppression in Hollow-Cup Machines

The ultra-precise stabilization spacecraft (UPSS) requires the use of hollow-cup machines (HCMs) with extremely low output torque ripple to achieve accurate attitude control. Conventional permanent magnet (PM) shaping methods are effective in suppressing torque ripple. However, they pose challenges such as magnetization difficulty and mechanical strength reduction. This paper proposes an inner rotor harmonic shaping (IRHS) method to reduce the torque ripple and avoid the defects of shaped PMs. This method is based on the adjustment effect of air-gap permeance harmonic injection on the air-gap flux density harmonics. To further explore the advantages of this method, this paper compares it with several PM shaping methods. A total of five machine topologies are considered, and their electromagnetic characteristics are comprehensively analyzed and compared. The proposed method reduces the torque ripple by 87% compared to conventional HCMs. Meanwhile, the comparison with several PM shaping methods shows that the IRHS achieves a 3% to 6% increase in the average torque and a 10% to 12% reduction in the PM loss while obtaining a comparable torque ripple. Finally, two prototype machines are manufactured and experimentally validated.