Nonlinear backstepping controller design for improving fault ride through capabilities of DFIG-based wind farms

This paper proposes a nonlinear backstepping control scheme to improve the fault ride through capability of a doubly fed induction generator (DFIG)-based wind farm by appropriately controlling the active and reactive power injection at the point of common coupling (PCC). The proposed nonlinear backstepping control scheme is used to derive the switching pulses for both rotor-side-converter (RSC) and grid-side-converter (GSC). The dynamical models of both GSC and RSC along with the dynamic of the DC-link voltage are used to derive the switching control actions with an aim of controlling active and reactive power injection. Such control actions improve the fault right through (FRT) capabilities of DFIG-based wind farms. The control Lyapunov functions (CLFs) are formulated at different stages of the controller design process as the negative definiteness or semi-definiteness of the derivatives of these CLFs guarantee the stability of the whole DFIG-based wind farm. Finally, simulation studies are carried out on a single machine infinite bus (SMIB)-based 9 MW wind farm with a DFIG in order to validate the performance of the proposed controller under the most severe three-phase short circuit fault on the system. Simulation results are also compared with an existing conventional proportional-integral (PI) controller in terms of active injection, reactive power support, sags in the PCC voltage, and fluctuations in the DC-bus voltage in order to demonstrate the superiority of the proposed control scheme.