Mitigation of SSR in Series-Compensated DFIG-Based Wind Farms with STATCOMs using a Nonlinear Backstepping Control Scheme

A nonlinear backstepping control scheme is proposed in this work for the voltage source converter (VSC) used with the static synchronous compensator (STATCOM) in a doubly fed induction generator (DFIG)-based series compensated wind farm in order to mitigate sub-synchronous resonance (SSR) and improve the transient stability. The proposed scheme will regulate the reactive power requirement either by absorbing or supplying through the STATCOM for alleviating the SSR. At the same time, the tracking of other properties representing the dynamics of the STATCOM will be ensured through the proposed controller. The control inputs for the proposed nonlinear STATCOM controller are derived in a way that these satisfy the Lyapunov stability theory and ensure the appropriate tracking of all dynamics associated with the STATCOM. Simulation studies are conducted to justify the theoretical aspects of the proposed control scheme by developing the series compensated and grid-connected DFIG-based wind farm with the STACOM using MATLAB/SIMULINK platform. The high compensation level is considered for evaluating the performance under the worst case operating condition and the performance is compared with a traditional but finely tuned proportional integral (PI) controller in terms of eliminating fluctuations due to the SSR in the output responses of the DFIG-based wind farm.