Efficient nonlinear integral backstepping control for doubly fed induction generators-based wind farm under unbalanced electrical grid voltage

Abstract

This paper proposes a modified and efficient control strategy for wind farm (WF) based on doubly-fed induction generators (DFIGs) under an unbalanced electrical voltage grid. This strategy consists of two loops: the main and the auxiliary. The main loop controls the positive sequence currents of the rotor and grid-side converter (GSC) of each DFIG in the WF. In contrast, the auxiliary one is designed to regulate negative sequence currents. In this work, the positive and negative sequences of the rotor current loops of each DFIG in the WF are regulated using a nonlinear integrated backstepping controller (IBSC). The main contribution of this strategy is to ensure that the WF remains connected to the grid under severe asymmetrical faults, to reduce the oscillations caused by such faults in the electromagnetic torque, in the WF power profile, and in the DC bus voltage. Additionally, it aims to minimize the total harmonic distortion (THD) in currents of WF and enhance the power quality. To verify these objectives, the suggested strategy is compared with a single-loop strategy. This comparative study is validated through simulations performed in Matlab/Simulink software, using the S-function builder which enables its integration into actual control boards for tests under real environment.