Investigation of Rotor Holes on the Performance of Hybrid-Magnet Interior Permanent Magnet Synchronous Machines

Hybrid-magnet multilayer interior permanent magnet synchronous machines (IPMSMs) offer reduced rare-earth magnet usage while maintaining high torque density; however, flux crowding and localized saturation in multilayer rotor structures can lead to increased core loss and torque ripples. This paper investigates hole-based rotor modification in a double U-shaped hybrid-magnet IPMSM to improve flux distribution and electromagnetic performance. A magnetic equivalent circuit (MEC) interpretation is employed to explain the influence of pole-arc hole insertion on air-gap flux and rotor saturation behaviour. Finite-element analysis (FEA) is conducted to evaluate the effects of hole location, number, size, and arrangement on torque ripple, core loss, efficiency, and mechanical integrity. Based on this investigation, a multi-objective optimization using the non-dominated sorting genetic algorithm II (NSGA-II) is performed to determine the optimal hole geometry under electromagnetic and mechanical constraints. A 1-kW prototype with a hybrid-magnet-based, Holes based topology is fabricated, and measured back-EMF and MTPA current-controlled operation validate the proposed rotor modification approach.