Robust Nonlinear Optimal Control of DFIG based Wind Turbine

In this paper, based on the state-dependent Riccati equation (SDRE) technique, two nonlinear suboptimal controllers (a regulator and a tracker) are designed for a wind turbine with doubly fed induction generator (DFIG). The control objectives include increasing the system stability margin and setting of the electromagnetic torque and the stator reactive power signals to the desired values. In the designed procedure of the controller, a nonlinear model is used for modeling the dynamical properties of the considered DFIG. The performance of the designed controllers to improve the system stability is evaluated in MATLAB software through some simulations for different working conditions of the wind turbine. In addition, an eigen-analysis of the closed-loop system is carried out to evaluate the effects of the proposed SDRE controller on the system stability. The performance of the designed SDRE tracking controller is also investigated through some simulations. In closing, simulation results demonstrate the effectiveness and robustness of the proposed SDRE controllers.