*Article* **Variable-Gain Super-Twisting Sliding Mode Damping Control of Series-Compensated DFIG-Based Wind Power System for SSCI Mitigation**

**Ronglin Ma, Yaozhen Han \* and Weigang Pan \***

> School of Information Science and Electrical Engineering, Shandong Jiaotong University, Jinan 250357, China; maronglin@sdjtu.edu.cn

**\*** Correspondence: hanyz@sdjtu.edu.cn (Y.H.); 205036@sdjtu.edu.cn (W.P.); Tel.: +86-0531-8068-7920 (Y.H. & W.P.)

**Abstract:** Subsynchronous oscillation, caused by the interaction between the rotor side converter (RSC) control of the doubly fed induction generator (DFIG) and series-compensated transmission line, is an alleged subsynchronous control interaction (SSCI). SSCI can cause DFIGs to go offline and crowbar circuit breakdown, and then deteriorate power system stability. This paper proposes a novel adaptive super-twisting sliding mode SSCI mitigation method for series-compensated DFIGbased wind power systems. Rotor currents were constrained to track the reference values which are determined by maximum power point tracking (MPPT) and reactive power demand. Super-twisting control laws were designed to generate RSC control signals. True adaptive and non-overestimated control gains were conceived with the aid of barrier function, without need of upper bound of uncertainty derivatives. Stability proof of the studied closed-loop power system was demonstrated in detail with the help of the Lyapunov method. Time-domain simulation for 100 MW aggregated DFIG wind farm was executed on MATLAB/Simulink platform. Some comparative simulation results with conventional PI control, partial feedback linearization control, and first-order sliding mode were also obtained, which verify the validity, robustness, and superiority of the proposed control strategy.

**Keywords:** subsynchronous control interaction; super-twisting sliding mode; variable-gain; doubly fed induction generator
