Super-Twisting Control for a Doubly Fed Induction Generator (DFIG)-Based Wind Turbine Using a Nonlinear Observer

The high cost and complexity of using sensors for controlling processes have led to the development of observer techniques that aim to estimate system states without the need for sensors. These techniques reduce system complexity and can potentially reduce product and maintenance costs. In this paper, we present an interconnected high gain observer (IHGO) that estimates the electromagnetic torque, speed, and position of a doubly fed induction generator-based wind turbine (DFIG-WT) using only voltage, current, and wind speed measurements. The IHGO is designed to be robust to parameter uncertainties and its stability is assessed using Lyapunov theory. To guarantee finite time convergence, a Super Twisting-based High Order Sliding Mode (ST-HOSM) controller is used for direct torque control. The ST-HOSM is a simple algorithm that maintains the sliding mode characteristics, provides robustness against disturbance, and reduces the chattering phenomenon. The controller and observer are designed in the frame to avoid the use of a phase-locked loop (PLL). Simulation results confirmed the effectiveness of the proposed control strategy under parameter uncertainties, power and speed variations, grid voltage dip and current sensor noise.