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

Sammanfattning

Permanent magnet synchronous machines (PMSMs) are widely used in heavy-duty electricpowertrains due to their high efficiency and torque density. However, conventional NdFeBrotor magnets often contain heavy rare earth elements (HREs), such as dysprosium andterbium, to improve coercivity and in turn thermal stability. This thesis evaluates thefeasibility of removing HREs from NdFeB magnets in a double-layer V-shaped PMSMrotor. The work combines a sustainability analysis of rare earth elements (REEs) withelectromagnetic simulations in Ansys Motor-CAD, including magnet screening, demagnetizationassessment, custom magnet evaluation, rotor geometry studies, optimization, andbenchmarking 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, HREreduction does not remove all sustainability challenges, since REE supply remains affectedby geopolitical concentration, processing capacity, environmental risks, and low recyclingrates. The simulation results show that replacing the original HRE-based magnet withavailable HRE-free magnets in the unchanged rotor geometry is not sufficient to meetboth 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 and320 Nm after demagnetization, compared with approximately 505 Nm for the HRE-basedreference design. High intrinsic coercivity, and strong coercivity retention at elevatedtemperatures are critical for limiting irreversible demagnetization under short circuitcondition. Rotor geometry optimization significantly improves the HRE-free designs,especially through increased magnet thickness up to 6.00 mm, but introduces trade-offsbetween demagnetization resistance, torque performance, and magnet weight. Overall,the results show that an HRE-free PMSM rotor application is possible only if magnetmaterial properties and rotor geometry are designed together.