Robust Active Defense Control for Wide‐Frequency Oscillation in Direct‐Drive Wind Power Systems Based on NFTSMC under Low SCR Conditions

With the growing penetration of renewable energy in dual‐high power systems, the interaction between direct‐drive permanent magnet synchronous generator (PMSG) wind turbines and weak AC grids causes critical stability problems, especially wide‐frequency oscillation caused by converter control coupling and time‐varying grid impedance. Conventional linear active damping with fixed parameters cannot handle large parameter perturbations and digital control delays. This paper presents a novel active defense control scheme based on nonsingular fast terminal sliding mode control (NFTSMC) for PMSG wind farms. A detailed impedance model considering digital delay is built to reveal the high‐frequency instability mechanism under low short‐circuit ratio. Grid impedance variations and delays are treated as lumped bounded disturbances, and a robust NFTSMC law is designed with Lyapunov proof to achieve finite‐time convergence and reshape converter impedance, avoiding singularity. Hardware‐in‐the‐loop results validate that the proposed method suppresses resonance, limits current distortion to meet grid codes, and improves system robustness under extremely weak grid conditions.