Model-Free Fast Integral Terminal Sliding Mode Control for Maximum Power Point Tracking With High-Order Disturbance Observer in WECSs

This paper proposes a novel model-free fast integral terminal sliding mode control (MFFITSMC) strategy for permanent magnet synchronous generators (PMSGs) to achieve maximum power point tracking (MPPT) in wind energy conversion systems (WECS) without anemometers. An ultra-local model (ULM) is constructed for the speed and current loops, which forms the basis of the proposed controller. To address system uncertainties and aerodynamic torque disturbances, a High-Order Disturbance Observer (HODO) is developed and integrated into the control loop for real-time disturbance estimation and compensation. The key feature of the MFFITSMC controller is its PID-based sliding surface, where the integral term is enhanced with an exponential function to accelerate error convergence and improve tracking precision. Combined with the HODO, which rapidly estimates high-order disturbances, the controller achieves accurate reference tracking, suppresses oscillations around the optimal operating point, ensures fast convergence, and optimizes control effort. Quantitative simulation results under severe parameter mismatch demonstrate the superior robustness of the proposed scheme. Specifically, the proposed controller reduces the rotor speed tracking error to merely 0.0061%, significantly outperforming the Super-Twisting SMC (0.2985%) and Linear Quadratic Regulator (0.1828%). Additionally, it maximizes power extraction efficiency with a negligible mechanical power error of 0.0003% (compared to 0.2437% for STSMC and 0.1929% for LQR), confirming its capability to ensure optimal performance despite internal and external disturbances.