Design and Optimization of an External Rotor Ironless BLDCM Used in a Flywheel Energy Storage System

Based on the application requirements of a flywheel energy storage system, an external rotor ironless brushless dc machine (BLDCM) is designed and optimized. The finite element method is adopted to investigate the external rotor ironless BLDCM. Performance improvement and loss minimization of the machine are achieved through optimizing the magnetic pole and the winding. The research results show that the copper loss of the machine can be reduced by appropriate selection of magnetic steel thickness even under the condition that the main parameter of the flywheel machine is set. Proper choice of the magnetic steel polar-arc coefficient is beneficial to reduce the flux leakage on the surface of the rotor. The width of air-gap flux density can be increased by reasonable selection of magnetic poles and magnetizing style. The flywheel energy storage machine prototype is fabricated based on the optimized design of the machine. The experiment results show that the test results coincide well with the design requirements.