Modified rotor-side converter control design for improving the LVRT capability of a DFIG-based WECS

Abstract

The rapid integration of wind-power generation with existing power grids has caused reliability and stability concerns owing to the negative impact on the dynamic behaviors of power systems. During a fault, large electromotive force is induced in the rotor circuit of a doubly fed induction generator (DFIG) as the circuit is highly vulnerable to it. Such circumstances increase the importance of the low-voltage ride-through (LVRT) capability of a DFIG to ensure stability of the electric grid during transient conditions. Considering these factors, this study focuses on the mitigation of rotor overcurrents and DC-link voltage variations by modifying the control structure of the DFIG converter, thereby enhancing its LVRT capability. Additional voltage terms are injected into the rotor-voltage references to improve the transient behavior of the DFIG control system. In the proposed design, transient rotor currents and DC-link voltage variations are effectively suppressed. Because the voltage terms are introduced outside the current loops, there is no impact on their stability. Furthermore, electromagnetic torque oscillations during the faults are considerably suppressed. Finally, the validity of the proposed design during abnormal grid conditions is demonstrated via MATLAB/Simulink. The results confirm the feasibility and effectiveness of the improved converter control design to enhance the LVRT capability of a DFIG.