On the state-dependent switched energy functions of DFIG-based wind power generation systems

This paper proposes a novel state-dependent switched energy function (SdSEF) for general nonlinear autonomous systems, and constructs an SdSEF for doubly-fed induction generator (DFIG)-based wind power generation systems (WPGSs). Different from the conventional energy function, SdSEF is a piece-wise continuous function, and it satisfies the conditions of conventional energy functions on each of its continuous segments. SdSEF is designed to bridge the gap between the well-developed energy function theory and the description of system energy of complex nonlinear systems, such as power electronics converter systems. The stability criterion of nonlinear autonomous systems is investigated with SdSEF, and mathematical proof is presented. The SdSEF of a typical DFIG-based WPGS is simulated in the whole processes of a grid fault and fault recovery. Simulation results verify the negativeness of the derivative of each continuous segment of the SdSEF.