Sub-Synchronous Damping by Battery Storage System in Grid Forming Control Mode

A wind farm is susceptible to sub-synchronous oscillation (SSO) issue due to the interaction between the wind turbine grid-side converters and the grid under weak grid condition. By integrating grid-forming (GFM) controlled battery energy storage system (BESS) into the wind farm at the common coupling point (PCC), the SSO might be suppressed. Impedance analysis indicates that increasing damping coefficient of GFM control helps to better suppress SSO. However, increasing damping coefficient will increase droop coefficient simultaneously, leading to higher power peak and droop under frequency deviation. Consequently, higher converter capacity and more batteries are needed to meet power requirement, causing undesirable higher cost. In this paper, a new control method is proposed to decouple damping and droop coefficients. Therefore, lower power peak and droop constant can be realized under frequency deviation to save costs for BESS. Experimental and simulation results are provided to verify the effectiveness of the proposed method.