Comparative Evaluation of Performance Trade-Off Under Permanent Magnet Volume Reduction in SPM, IPM, and PM-Assisted SynRM

Abstract

Rising costs, supply uncertainty, and geopolitical dependence associated with rare-earth permanent magnets have created an urgent need to reduce permanent magnet (PM) usage in electric machine designs while maintaining high electromagnetic performance. This paper presents a comprehensive comparative investigation of PM reduction strategies for three widely adopted traction machine topologies: Surface Permanent Magnet (SPM), Interior Permanent Magnet (IPM), and Permanent Magnet-Assisted Synchronous Reluctance (PMASynRM) machines. We developed a unified evaluation framework by integrating each machine’s electromagnetic characteristics, electrical operating constraints, and practical inverter limitations across a wide operating speed range. Finite element analysis (FEA) is employed to systematically investigate the effects of progressive PM volume reduction by independently varying magnet width and length while keeping stator geometry, winding configuration, material properties, and operating conditions. We reduced PM dimensions from 100% to 30% of the baseline design to evaluate their impact on torque-speed characteristics, efficiency, and flux-weakening capability. The results reveal that the impact of PM reduction depends strongly on both machine topology and the magnet reduction strategy. Across all machine topologies, reducing magnet width consistently preserves higher torque capability, efficiency, and high-speed operating performance compared with reducing magnet length. Among the machines investigated, the SPM topology exhibits the greatest sensitivity to PM reduction, particularly in the constant-torque region, owing to its complete reliance on permanent magnet excitation. In contrast, the IPM and PMASynRM machines show much greater tolerance to reduced PM volume because the additional contribution of reluctance torque from rotor saliency improves torque retention, extends the constant-power speed range, and reduces efficiency degradation. These findings provide valuable design insights into the trade-offs between permanent magnet utilization and machine performance, offering practical guidelines for minimizing rare-earth material consumption while maintaining competitive traction performance in next-generation electric vehicles and other sustainable electrification applications.

The authors' abstract, as published at the source. Applied Sciences, 2026 · DOI ↗