Nonsingular fast terminal sliding mode control for direct-drive permanent magnet wind power systems based on an inverse hyperbolic sine extended state observer

To address the strong nonlinearity, parameter perturbations, and stochastic wind disturbances in direct-drive PMSG wind power systems operating below the rated wind speed, this paper proposes a composite speed-tracking control strategy integrating an improved extended state observer (ESO) with nonsingular fast terminal sliding mode (NFTSM) control. An improved NFTSM sliding surface and a composite reaching law are designed to achieve finite-time convergence while suppressing chattering. The inverse hyperbolic sine ( ar sinh) function replaces the conventional piecewise fal function within the ESO, yielding a globally smooth observer that eliminates estimation chattering and phase lag caused by derivative discontinuities. The disturbance estimate is fed forward to the sliding mode controller for dynamic compensation, with finite-time convergence on the sliding manifold and closed-loop stability rigorously proved. Simulations under ramp, gust, and natural wind conditions show that, compared with PI and ADRC, the proposed strategy reduces speed regulation time by 26.3% and power coefficient recovery time by 27.4% on average; compared with fal -ESO-based sliding mode control, speed tracking accuracy improves by 21.4% and response speed by 14.3%. Experimental platform results confirm the simulation findings.