Nonlinear rotor kinetic energy control strategy of DFIG-based wind turbine participating in grid frequency regulation

Abstract

Large-scale wind power integration reduces the level of inertia in power systems, significantly deteriorating their frequency stability. To address this issue, a nonlinear rotor kinetic release control strategy is designed for wind power grid-connected systems based on an extended state observer (ESO) and nonlinear feedforward state feedback transformation (NFSFT) theories. First, the affine nonlinear system of a DFIG-based wind turbine participating in grid frequency regulation is established. The system is transformed into a basic equivalent linear system based on the NFSFT theory, and a nonlinear control law is obtained. Second, the ESO is used to observe the generalized disturbance composed of the complex parameter operation required by the nonlinear control law, which circumvents the huge computational burden of the nonlinear control law and the unknown uncertainty of the system. Finally, a limiting link and speed control link are added to prevent excessive release of the kinetic energy of the wind turbine rotor and complete the wind turbine speed recovery. A wind power grid-connected system is built using MATLAB / SIMULINK for simulation verification. The results show that the proposed strategy exhibits a better frequency regulation effect than other strategies.