Abstract: A state of charge（SOC）recovery control strategy based on improved second-order filter power allocation is proposed for hybrid energy storage system composed of supercapacitor and battery energy storage. Firstly,the power allocation process of the traditional first-order low-pass filter algorithm is analyzed,and the second-order filter transfer function with power error feedback loop is constructed to eliminate the integral effect of the traditional first-order low-pass filter in response to the high frequency power instruction and improve the tracking control effect of the hybrid energy storage system on the target power instruction. Then,taking the normalized SOC of hybrid energy storage system as the control index,a new adjustment rule of filtering time constant is formulated to dynamically optimize the power allocation command of hybrid energy storage system. The simulation results show that the control strategy can effectively suppress the fluctuation of wind power grid-connected power,maximize the available capacity of supercapacitor energy storage,and prolong the service life of battery.