Research on Multi-Physical Fields of High-Power PMSM/G Used for FESS During the Process of Controllable Charging and Uncontrollable Discharging

Flywheel energy storage system (FESS) has been widely used in many fields, benefiting from the characteristics of fast charging, high energy storage density, and clean energy. Uncontrollable discharging system can be used in some special occasions which doesn't have strict requirements on the power quality, such as electric heaters, emergency power supplies, etc. Taking a charging and discharging (C&D) system of 200 kW 15000 rpm high-speed Permanent Magnet Synchronous Motor/Generator (PMSM/G) used for FESS as an example, field-circuit coupling calculation model of PMSM/G during the process of controllable charging and uncontrollable discharging is established. And then the relationships between speed and current-voltage during charging process is calculated. A variable load calculation method based on transient electromagnetic field during the process of uncontrollable discharging is presented, and the eddy current field and transient temperature field of rotor sleeve and permanent magnets during the process of C&D under different loads are also calculated. The output characteristic curves of FESS under condition of constant loads during the process of uncontrollable discharging is drawn. The conjugate analysis method of rotor multi-physical fields is proposed to study the relationships between rotor sleeve stress and eddy current distribution, and the optimized sleeve thickness for high-speed PMSM/G is also presented. Also, a solution is presented to solve the temperature and sleeve fracture problems caused by eddy current under high-speed operation. This contents of the paper can provide references for efficient and reliable design of PMSM/G under extreme conditions used for FESS.