Multi-Physics Design Optimization and Predictive Thermal-Electromagnetic Control of Rare-Earth-Free Synchronous Reluctance Machines for High-Efficiency Drives

Abstract

The vulnerability of rare-earth permanent magnet supply chains has accelerated the need for high-performance, rare-earth-free electric drives in industrial and traction applications. Synchronous reluctance machines offer robust rotor construction and zero rotor copper losses, but their commercial adoption is hindered by lower torque density, torque ripple, and nonlinear magnetic saturation under heavy electrical loading. Existing control frameworks treat electromagnetic modulation and thermal-mechanical stress analysis independently, which often results in acoustic noise, sub-optimal flux-barrier geometries, and insulation degradation. This paper presents an integrated multi-physics design and predictive control architecture for rare-earth-free synchronous reluctance machine drives. We formulate an asymmetric rotor flux-barrier optimization using coupled finite element analysis and computational fluid dynamics to maximize torque density while enforcing von Mises mechanical stress limits at high rotational speeds, and we couple this to a lumped-parameter stator hot-spot thermal model whose temperature-dependent winding resistance feeds back into the electromagnetic and control equations. For operational control, we develop a finite-control-set model predictive control algorithm that directly incorporates nonlinear cross-saturation inductances, a thermal current-derating constraint driven by the hot-spot model, and an online high-frequency signal-injection insulation diagnostic observer. Experimental validation on a 45-kW prototype demonstrates that the proposed drive achieves ultra-premium efficiency class performance with 96.8% peak efficiency, reduces torque ripple from 14.2% to 3.8%, and detects stator winding inter-turn short-circuit precursors at a normalized impedance deviation of 0.5%.