Decentralized nonlinear control of wind turbine with doubly fed induction generator

In this paper, a novel nonlinear control design method for the wind turbine (WT) with doubly fed induction generator (DFIG) using differential geometry theory is proposed. The WT with DFIG is represented by a third-order model where electromagnetic transients of the stator are neglected. Then the model is exactly linearized using the coordinate transformation in differential geometry theory. Since the relative degree of the model of the WT with DFIG is equal to the order of the original system model, the linearized model can be transformed into the Bronovsky norm form. The linear quadratic regulator (LQR) design method is introduced to design the optimal control for the linearized system, and the nonlinear control for the WT with DFIG obtained by the inverse coordinate transformation only depends on the parameters of the WT with DFIG. Hence, the nonlinear control can be considered as a decentralized control, which is a desirable feature for a WT with DFIG. To illustrate the effectiveness of the nonlinear controller proposed, simulations on a single machine infinite bus (SMIB) system and a four-machine system are performed. Compared to the conventional PI control, the proposed nonlinear control can improve the transient stability of the power systems and enhance the system damping.