Abstract
Series-compensated transmission lines can trigger Sub-Synchronous Resonance (SSR) in Doubly-Fed Induction Generator (DFIG)-based wind farms by coupling network resonance with generator torsional modes. Conventional control strategies often rely on linearized models and regulate the Rotor-Side Converter (RSC) and Grid-Side Converter (GSC) independently, limiting robustness and damping capability. This paper proposes a coordinated Adaptive Sigmoid-Modulated Nonlinear Integral Terminal Sliding Mode Controller (ASM-NITSMC) that reallocates damping in real time between the RSC) and GSC via a bounded participation factor. The core novelty lies in a damping participation mechanism that dynamically allocates SSR damping responsibility between the RSC and GSC based on instantaneous DC-link voltage deviation and converter loading a feature absent in existing NITSMC and adaptive SMC schemes. The proposed controller combines a NITSMC law with a sigmoid-based reaching strategy to ensure finite-time convergence without singularity issues, robust to parameter variations and external disturbances, and mitigates chattering via sigmoid-based smoothing. A nonlinear control-oriented model in the dq-domain is developed, and global asymptotic stability is established using Lyapunov theory. Compared with a feedback linearization SMC and an uncoordinated nonlinear design, it reduces DC-link voltage deviation by up to 51.5%, halves power/torque overshoot (up to 50%), and shortens damping time by up to 35%, while achieving the lowest IAE/ITAE/ISE/ITSE across all cases. During fault-ride-through, it delivers faster active-power recovery, stronger reactive-power support, and more stable DC-link regulation than a non-singular fast TSMC. The ASM-NITSMC is implementation-efficient and suitable for digital control platforms, making it attractive for real-time applications in modern wind farms.