Bearing Stiffness Analysis of Bearingless Flux-Switching Permanent Magnet Motor With Five Degrees of Freedom Rotor Magnetic Suspension

The bearingless flux-switching permanent magnet motor with five degrees of freedom rotor magnetic suspension (5-DOF-BFSPMM) is particularly suitable for high-capacity and high-speed applications. To ensure the smooth operation of the rotor, it is crucial to prevent the motor from operating within the critical speed range, which is influenced by the bearing stiffness. Therefore, this paper proposes a comprehensive study on the bearing stiffness of 5-DOF-BFSPMM, and a stable operation control strategy based on the relationship between bearing stiffness and critical speed is developed. Firstly, the motor's structure and the principles are introduced. Then, the theoretical model of bearing stiffness is established based on the research of the internal relationship among the motor's structural parameters, electrical parameters and bearing stiffness. After that, the relationship between bearing stiffness and critical speed is presented. Finally, based on the linear active disturbance rejection control theory, a 5-DOF magnetic suspension and rotation control strategy is designed to avoid the critical speed range. The effectiveness of the theoretical model and control strategy is validated through finite element simulations and experimental results.