The supplementary damping control (SDC) is added to the q-axis output of RSC's inner controller. This method was proposed by Andres E.Leon in 2016. The method consists of gain, lead-lag compensator, and band-pass filter. The measured active power is adopted as an input signal. For more information, you can read the following paper by Andres E.Leon.
Integration of DFIG-Based Wind Farms Into Series-Compensated Transmission Systems
Naeem GH (2020). SSR damping in a DFIG-based wind farm by adding SDC in RSC. (https://www.mathworks.com/matlabcentral/fileexchange/73831-ssr-damping-in-a-dfig-based-wind-farm-by-adding-sdc-in-rsc), MATLAB Central File Exchange. Retrieved .