Design and Evaluation of a HRE-Free PMSM Rotor for Heavy-Duty Applications A Combined Literature and Simulation Approach Considering HRE-Free Rotor Design

Abstract

Permanent magnet synchronous machines (PMSMs) are widely used in heavy-duty electric powertrains due to their high efficiency and torque density. However, conventional NdFeB rotor magnets often contain heavy rare earth elements (HREs), such as dysprosium and terbium, to improve coercivity and in turn thermal stability. This thesis evaluates the feasibility of removing HREs from NdFeB magnets in a double-layer V-shaped PMSM rotor. The work combines a sustainability analysis of rare earth elements (REEs) with electromagnetic simulations in Ansys Motor-CAD, including magnet screening, demagnetization assessment, custom magnet evaluation, rotor geometry studies, optimization, and benchmarking against the original HRE-based reference design. The sustainability analysis shows that reducing HRE content can lower material cost, reduce environmental burden, and decrease dependence on critical REEs. However, HRE reduction does not remove all sustainability challenges, since REE supply remains affected by geopolitical concentration, processing capacity, environmental risks, and low recycling rates. The simulation results show that replacing the original HRE-based magnet with available HRE-free magnets in the unchanged rotor geometry is not sufficient to meet both torque and demagnetization requirements. At 140◦C under short circuit conditions, the original HRE-free 45SH and 42SH rotor cases reached only approximately 335 Nm and 320 Nm after demagnetization, compared with approximately 505 Nm for the HRE-based reference design. High intrinsic coercivity, and strong coercivity retention at elevated temperatures are critical for limiting irreversible demagnetization under short circuit condition. Rotor geometry optimization significantly improves the HRE-free designs, especially through increased magnet thickness up to 6.00 mm, but introduces trade-offs between demagnetization resistance, torque performance, and magnet weight. Overall, the results show that an HRE-free PMSM rotor application is possible only if magnet material properties and rotor geometry are designed together.