I. Introduction
Lithium battery ESS (energy storage system) based on VSI (Voltage Source Inverter) control is popular for its unique superiority [1]. PCS (Power Conversion System) are usually fed into the power system through LCL filters. Because the high-order LCL filter contains multiple resonant frequencies, the system stability will deteriorate if the resonant frequency is too low due to the unreasonable design of the LCL filter [2], [3]. In addition, if the damping is not proper, the interaction between multiple VSI in DERs (Distributed Energy Resources) will also affect the system stability [4], [5]. Therefore, it is necessary to design a reasonable control strategy to improve the impedance characteristics of the system and improve its stability margin, so that the microgrid can obtain better dynamic response characteristics.