Design and Analysis of Novel Bearingless Permanent Magnet Synchronous Motor for Flywheel Energy Storage System

To effectively simplify system structure and improve power density and efficiency, a design for a motor/generator suitable for flywheel energy storage system (FESS) is proposed. The machine is an outer-rotor and coreless-stator-type bearingless permanent magnet synchronous motor (BPMSM) with a Halbach array. Firstly, the operation principle of the outer-rotor BPMSM is described. Then, the structure and performance of the Halbach permanent magnet (PM) array are analyzed. The airgap magnetic field, back-EMF, suspension force, unilateral magnetic pull force and electromagnetic torque are calculated and analyzed by the finite element analysis (FEA). Finally, it is verified that the magnetic field of the suspension force windings increases the rotor eddy current loss by transient FEA coupled with external circuit. The rotor eddy current losses of BPMSM with different structures are compared. The comparison results show that the rotor eddy current loss of the coreless-stator-type BPMSM with Halbach array is the lowest. The simulation results verify the theoretical analysis and structure design, which can provide reference for the application of the motor in the FESS.