Design and Analysis of a High-Specific-Power PMSM with Direct Liquid Cooling

Abstract

The demand for high-specific-power electrical machines in aerospace and advanced mobility applications requires pushing the boundaries of rotational speed and electrical loading, which introduces severe mechanical and thermal challenges. To address these bottlenecks, this paper proposes a high-specific-power permanent magnet synchronous machine (PMSM) that combines an outer-rotor topology with a direct liquid cooling (DLC) stator architecture. Moving beyond previous component-level investigations, the primary contribution of this study is the comprehensive, system-level multi-physics design and validation of this integrated machine. The outer rotor inherently retains the magnets against centrifugal forces without requiring a non-magnetic retaining sleeve, while the internal stator provides a platform for leak-free coolant routing directly through hollow Litz wire conductors that compose DLC winding. A detailed multi-objective optimization framework coupling finite element analysis and genetic algorithms is employed to maximize average torque while minimizing torque ripple and active mass. Compre-hensive electromagnetic and thermal validations demonstrate that the optimized machine delivers 600 kW of continuous power at a base speed of 6000 rpm, achieving a highly competitive specific power of 18 kW/kg. Furthermore, the DLC system effectively manages the extreme thermal loads, maintaining a maximum hotspot temperature around $\mathbf{1 2 0}^{\circ} \mathbf{C}$, thereby proving the viability of the proposed architecture for next-generation applications.