Equivalent Magnetic Circuit Reluctance Optimization for Rotor Loss Reduction in Permanent Magnet Synchronous Motor for UPS-FESS

Due to poor heat dissipation of rotor, especially in flywheel energy storage system (FESS) for uninterruptible power supply (UPS), there is a higher risk of irreversible demagnetization by rotor temperature rising. Irreversible demagnetization of permanent magnets by rotor loss always is a critical problem of high-speed permanent magnet synchronous machine (PMSM). The stabilization and efficiency can be increased by reduction of rotor loss. By Finite Element Method simulations with experiment date, the rotor temperature rising of the prototype PMSM mainly comes from rotor loss induced by time harmonic. The distribution and components of prototype rotor loss are given. Rotor loss is analyzed by equivalent magnetic circuit with considering time harmonic magnetomotive force in this paper. According to analysis of rotor loss, this paper presents a method to reduce rotor loss without changing stator structure and winding current. This rotor structure optimization will not affect output performance of PMSM. The method has been proved to be available by the no-load experiment finally. It can greatly reduce the rotor loss in no-load operation when PMSM is driven in high-speed operation zone.