Doubly-fed induction generator (DFIG) based wind turbine generation system (WTGS),a standard wind power conversion system choice, has been extensively used to get the extreme power conversion efficiency, with reduced capacity of power converters and full controllability of stator powers [
1], due to their features such as variable speed operation. The stator winding terminals are directly connected to the grid, while the rotor winding terminals are fed via a two bidirectional converters connected in back to back. Between these two converters, there is a DC-link capacitor filter which works as energy storage in order to maintain the DC-link voltage ripple small. The DFIG based WTGS is a dynamical system with highly nonlinear and coupled characteristics, with time-varying and uncertain inputs [
2]. The objectives of the WTGS controllers depend upon the operating mode defined by wind speed [
3]. For low wind speed, it has to maximize the captured wind power, while above the rated wind speed it has to limit the generated power and the rotational speed in order to protect the mechanical parts of the WTGS [
4].