An Enhancing Grid Stiffness Control Strategy of STATCOM/BESS for Damping Sub-synchronous Resonance in Wind Farm Connected to Weak Grid

Under weak grid, wind farm can easily cause subsynchronous resonance (SSR) owing to the impedance interaction between wind farm and grid. In this article, a synchronous compensator with battery energy storage system (STATCOM/BESS) is connected in parallel with grid to suppress this SSR. Meanwhile, analogizing virtual synchronous generator (VSG), an enhancing grid stiffness control strategy is proposed for STATCOM/BESS with low rated active power and high rated reactive power. According to the designed control strategy, the demand quantity of battery for STATCOM/BESS can be reduced by more than 50%, which can decrease the costs and simultaneously improve the security. Since the impedances of grid and STATCOM/BESS controlled by the designed control strategy both are basically inductive, the parallel impedance of grid and STATCOM/BESS is smaller than the single grid impedance, which equivalently enhances grid stiffness from the point of view of impedance. Moreover, as the proposed suppression method of SSR does not need to modify other controllers of power station nor detect harmonics, it is a general suppression method of the SSR induced by impedance interaction between power station and weak grid. Finally, experimental results verify the validity of the proposed suppression strategy for SSR.