A review of structural design for reduced-rare-earth permanent magnet motors in new energy vehicles

This review examines structural design strategies for reducing or eliminating rare-earth content in traction motors for new energy vehicles (NEVs). The analysis covers magnet-free topologies—synchronous reluctance motors (SynRMs), switched reluctance motors (SRMs), externally excited synchronous motors (EESMs), and induction motors (IMs)—together with reduced-rare-earth alternatives, including ferrite-assisted synchronous reluctance motors (PMaSynRMs), hybrid rare-earth/ferrite configurations, and emerging iron nitride magnets. For each topology, the electromagnetic and mechanical design trade-offs are analyzed, with particular attention to demagnetization resistance, torque density, efficiency, and manufacturability. The review finds that PMaSynRMs currently offer the best cost-performance balance for mass-market traction, EESMs provide mature rare-earth-free operation with dynamic flux control validated by commercial deployment, and IMs remain a proven magnet-free benchmark. Persistent barriers include irreversible demagnetization of low-coercivity magnets, mechanical deformation of flux-barrier rotors, and manufacturing scalability. Structural measures—optimized flux barriers, spoke-type magnet arrangements, direct oil cooling, and temperature-aware control—together with grain boundary diffusion and iron nitride magnets constitute the most promising pathways toward sustainable rare-earth-lean propulsion.