High-Speed, High-Specific Power Electric Machine for Aerospace Propulsion: Design, Optimization and Technology Demonstration

Abstract

The electrification of the transportation sector is rapidly transforming mobility technologies. While significant progress has been made in electrifying ground transportation, the aviation sector requires further research and development. Aviation significantly contributes to greenhouse gas emissions in the transportation sector. The number of passenger aircraft fleets is expected to double by 2037, causing a dramatic increase in emissions from the aerospace industry. To address these concerns, industry and academia increasingly focus on aircraft electrification to reduce pollution, lower maintenance costs, and enable more affordable and convenient air travel. Achieving full or hybrid electrification of commercial aircraft propulsion systems necessitates the development of megawatt-class electric machines, an area where research remains limited.

This thesis presents an electromagnetic design of a 1MW permanent magnet synchronous machine (PMSM) for aerospace propulsion. The design features an inner rotor, radial flux PMSM with a 36/6 slot-pole combination and an operating speed of 20000 rpm. Recognizing motor design's iterative and computationally intensive nature, this work proposes a multi-objective optimization strategy incorporating a neural network-based surrogate model and a genetic algorithm. This hybrid approach significantly reduces computational time compared to conventional finite element method-based optimization techniques. The optimized design achieves performance exceeding NASA's targets for aerospace propulsion, with an estimated electromagnetic specific power of 24.87 kW/kg and an efficiency of 98%. A comprehensive analysis of the machine's electromagnetic performance is also presented.

High-speed machines present significant electromagnetic, thermal, and mechanical design challenges. Limited by the project timeframe, as a technology demonstrator, a 150kW PMSM with the same slot-pole combination and operating speed is designed and developed. This demonstrator facilitated the investigation of pulse-width modulation (PWM) current effects on machine losses and enabled a detailed demagnetization analysis using 2D and 3D finite element analysis. The available test results for this motor are presented.