The low switching-to-fundamental frequency ratio (SFFR) control   strategy is adopted when the high-speed flywheel energy storage system (FESS) is used in urban rail transit system to provide network stability and regenerative braking energy recovery. The performance of the current control will be deteriorated or even the system instability may occur under low SFFR strategy. In this paper, a Low SFFR based direct voltage control strategy is proposed according to the unique characteristics of the high-speed FESS. The feasibility of the proposed method is analyzed, and the control parameters and the midpoint voltage balance method are designed. The effectiveness of the current stability and midpoint voltage balance is verified through simulations and experiments.

current stability, direct voltage control, FESS, low SFFR, urban rail transit system