Direct Power Controller Design for Improving FRT Capabilities of DFIG-Based Wind Farms using a Nonlinear Backstepping Approach

This paper proposes a new direct power control (DPC) strategy to improve the fault-ride through (FRT) capability of a doubly fed induction generator (DFIG)-based wind farm. A nonlinear backstepping approach is used to design controllers for grid-side converters (GSCs) and rotor-side converters (RSCs) to directly control the power (both active and reactive) injection at the point of common coupling (PCC). In this paper, the controller is designed by considering the dynamic of the DC-link voltage with the dynamics of active and reactive power for both the GSC and RSC rather than the dynamics of corresponding direct-and quadrature-axis currents. Though the main control objective is to provide adequate reactive power supports during the fault, the proposed scheme also ensures the frequency stability by delivering desired active power into the PCC. The proposed control scheme ensures the overall stability of the DFIG-based wind farm for which control Lyapunov functions (CLFs) are formulated during the different design steps and the stability is analyzed through the negative semi-definiteness of the derivative of these CLFs. Simulation studies are carried out on a DFIG-based wind farm to demonstrate the FRT capability of the proposed scheme during a three-phase short-circuit fault at the PCC. The performance of the proposed scheme is also compared with a sliding mode controller.