A Comparative Study of Inner Rotor and PM Shaping Methods for Torque Ripple Suppression in Hollow-Cup Machines

The ultra-precise stabilization spacecraft (UPSS) necessitates the use of hollow-cup machines (HCMs) with extremely low output torque ripple to achieve accurate attitude control. A recently proposed method, known as inner rotor sinusoidal shaping (IRSS), has been shown to effectively reduce torque ripple in HCMs while also mitigating the issues caused by existing permanent magnet (PM) shaping techniques, such as irreversible demagnetization and manufacturing complexity. To further explore the superiority of this method, this paper compares it with several PM shaping methods. A total of five machine topologies are included in this paper. The key parameters of these machine topologies are optimized using finite element method. Then, a comprehensive analysis and comparison about the electromagnetic characteristics of the five machines are conducted, such as open-circuit field distribution, open-circuit phase flux linkage, phase back electromotive force (back-EMF), and output torque. The results demonstrate that, compared to conventional PM shaping methods, the IRSS can achieve not only remarkably low torque ripple but also the highest average torque.