Abstract: In order to overcome the problems of power delay and power cycling caused by the traditional low-pass filter (LPF) power allocation strategy in the hybrid energy storage system(HESS) of urban rail transit, a power allocation strategy based on two-layer LPF is proposed for urban rail HESS. The first layer of LPF prevents the traction network from being impacted by removing the extreme components in the power fluctuation. The second layer adopts an improved second-order filter transfer function through LPF to optimize the cutoff characteristics at the handover frequency and eliminate the integral effect of the first-order filter during the high-frequency response. Compared with traditional methods, the double-layer filtering strategy can optimize the power output of energy storage devices, reduce overcharge and overdischarge phenomena, extend battery life, and improve the dynamic response capability of the system. The simulation results show that the proposed strategy can effectively improve the voltage stability, energy-saving rate and response speed of the traction network, while reducing the depth of battery charging and discharging and prolonging the service life of energy storage devices.

Key words: urban rail train, hybrid energy storage system, power allocation, dual-layer filter, energy management