Design, modeling, and validation of a 0.5 kWh flywheel energy storage system using magnetic levitation system

The flywheel energy storage system (FESS) has excellent power capacity and high conversion efficiency. It could be used as a mechanical battery in the uninterruptible power supply (UPS). The magnetic suspension technology is used in the FESS to reduce the standby loss and improve the power capacity. First, the whole system of the FESS with the magnetic levitation system is introduced, and the control diagrams of the charging/discharging processes are developed. Moreover, the force modeling of the magnetic levitation system, including the axial thrust-force permanent magnet bearing (PMB) and the active magnetic bearing (AMB), is conducted, and results indicate that the magnetic forces could stably levitate the flywheel (FW) rotor. The stator part and the FW rotor are analyzed using the FEM model, and the results could satisfy the requirements on stress and strength of the FESS at the rated speed. Then, the control models are established to accomplish the rapid charging/discharging functions of the FESS. Finally, experiments are performed to test the charging/discharging ability, and the results show that an excellent control current could enhance the charging/discharging efficiency so the stable DC link voltage could be outputted at the discharge process. Therefore, the test results prove that the designed FESS could be used as an auxiliary power supply for the UPS when the grid power fails.