Thermal and Mechanical Design of a High-Speed Power Dense Radial Flux Surface Mounted PM Motor

Abstract

With the growing need to meet aggressive emissions targets in the aerospace industry in the coming decades, the electrification of propulsion systems has become an area of great research and commercial interest. In order to achieve full electrification of larger commercial aircraft, it is critical to improve power and energy densities of components within the propulsion system. The power densities of electric motors are steadily rising to meet this requirement. Among the various motor designs available, the high-speed radial flux permanent magnet motor is presented as an architecture capable of achieving high efficiencies and power densities. Increasing power densities, however, poses challenges for the thermal management system as higher losses need to be dissipated from a relatively small machine package. One of the failure modes specific to permanent magnet motors is the demagnetization of the magnets in the rotor at higher temperatures which leads to a loss in performance. Therefore it is critical that the thermal management system of the rotor must effectively dissipate the losses generated in the magnets and other components within the rotor. This thesis discusses the mechanical and thermal design of a 150 kW high-speed radial flux surface mounted permanent magnet motor for aerospace propulsion applications. The thesis first introduces the current landscape of aerospace electrification, focusing specifically on electric and hybrid propulsion architectures, currently available electric motors for aerospace propulsion, and ongoing aircraft electrification projects. A review is then provided of the current state-of-the-art in rotor cooling designs for high-speed speed radial flux motors for traction applications before introducing the design of the motor proposed in this thesis. The discussion of the mechanical design provides a high level overview of the design, manufacturing, and assembly of the stator and rotating assemblies while the thermal design provides a brief overview of the stator cooling design and a deep dive on the rotor cooling design. Computational Fluid Dynamics (CFD) is used along with the Taguchi method for robust design to optimize the rotor cooling design for minimizing the magnet temperatures. Analysis for the optimized rotor cooling discussed is provided before providing recommendations for future work.