Stiffness analysis and levitation force control of the active magnetic bearing for a partially-self-bearing flywheel system

A compact flywheel energy storage system assisted by axial-flux partially-self-bearing permanent magnet motor has been proposed by the authors. The proposed machine combines axial magnetic bearing and motoring functionality into a single magnetic actuator, which not only spins the rotor-flywheel but also generates a levitation force to overcome the gravity. The mathematical model of the levitation force and stiffness of the active magnetic bearing are developed. The relationships between the stiffness and the key motor parameters are studied. High stiffness can be achieved for the special motor design. The derived force model is validated by finite element analysis. The control system of the levitation force is designed and experimental setup is built. The test results prove the correctness of the mathematical analysis and feasibility of the designed control system.