High-Speed Machine Design for Electric Turbochargers Based on General Air-Gap Field Modulation Theory

With the development of the automotive industry towards higher efficiency and lower emissions, electric turbocharged high-speed machines (HSMs) have garnered significant attention due to their potential to enhance power performance and fuel economy. This paper investigates a 5kW, 100,000r/min high-speed permanent magnet synchronous machine (HSPMSM) for electric turbochargers, focusing on its electromagnetic and mechanical performance. Firstly, based on the general air-gap field modulation theory (GAFMT), this study proposes a theoretical analysis method for cogging torque that considers machine slot-pole combinations. It reveals the relationship between magnetic field harmonics generated by modulation behavior and torque ripple, while elucidating the significance of magnetic field modulation in cogging torque generation. The proposed method is validated by comparing the results from finite element analysis (FEA), a preliminary selection of slot-pole combinations with low cogging torque and torque ripple is conducted. Secondly, a systematic and in-depth comparative analysis is conducted on six different slot-pole combinations, covering key performance indices such as no-load back electromotive force (EMF), cogging torque, losses, torque, and torque ripple. Moreover, the rotor's mechanical stress and dynamic performance under ultra-high-speed conditions are also evaluated. The most suitable slot-pole combination for electric turbocharger applications is identified through a comprehensive evaluation of electromagnetic performance, efficiency, and manufacturability. Finally, a prototype machine is manufactured, and experimental validation confirms the accuracy of the proposed analysis and modeling methods.