Research on loss optimization calculation and cooling structure design of high-speed permanent magnet motor rotor for integrated starter-generator

Hybrid propulsion systems, with their advantages such as strong endurance and high safety redundancy, have become an important research direction in the field of electric aircraft power. As a core component, the high-speed permanent magnet motor for integrated starter-generator must balance the requirements of aviation-level reliability and high power density, thus posing multiple challenges to motor design. This paper proposes a topology of surface-mounted permanent magnet motor without yoke, featuring stator overall oil immersion cooling and rotor carbon fiber binding. Firstly, the Halbach magnetization technology is utilized to optimize the number of radial segments of the permanent magnet and the magnetization angle of each segment, maximizing the closed-loop magnetic circuit within the rotor permanent magnet and equivalent to a rotor magnetic circuit without yoke. Secondly, a field-circuit co-simulation model is established to compare and analyze the contribution of sinusoidal wave excitation and PWM voltage source excitation to the rotor loss, and an equivalent calculation method for high-frequency PWM voltage/current waveforms is provided. Then, an electromagnetic-fluid thermal coupling CAE model is established to analyze the temperature rise distribution under the stator overall oil immersion cooling method, providing a quantitative basis for the controller output waveform requirements and permanent magnet grade selection. Finally, a 65 kW, 36,600 rpm prototype is developed and a high-speed back-to-back test platform is built to study the load generator loading method at a base frequency of 1220 Hz. The test results verify the reliability and practicality of the theoretical analysis method proposed in this paper, providing a sufficient theoretical basis for the development of oil-immersed cooling high-speed permanent magnet motor technology for integrated starter-generator.