Design and Optimization of Halbach-Array PM Rotor for High-Speed Axial-Flux Permanent Magnet Machine With Ironless Stator

In this article, a high-speed Halbach-array permanent magnet (PM) rotor for ironless stator axial-flux permanent magnet (AFPM) machine is proposed and researched with consideration of the multiphysics constraints, including the electromagnetic characteristics, mechanical strength, and rotor dynamics. Considering the severity of attractive force between twin rotors, the complex repulsive force among PM segments of Halbach-array and centrifugal force, the new hybrid sleeve, and PM fixation method are proposed to improve the rotor mechanical strength. Then, the rotor stress is analyzed by numerical analysis and three-dimensional (3-D) finite-element analysis (FEA). Furtherly, the sleeve thickness and interference fit are optimized by 3-D FEA. The rotor dynamics and bearing arrangement are analyzed to validate the effectiveness of the high-speed Halbach-array PM rotor. A 50-kW, 9000 r/min ironless stator AFPM machine prototype with Halbach-array PM rotor is manufactured and tested. The measured results show that the output power is up to 53.8 kW at 9000 r/min. The feasibility of high-speed Halbach-array PM rotor and accuracy of analysis method are validated by both simulated and measured results.