Enhanced crowbarless FRT strategy for DFIG based wind turbines under three-phase voltage dip

Abstract

This paper proposes a crowbarless low-voltage ride-through (LVRT) scheme for doubly-fed induction generator (DFIG) based wind turbines (WTs). The proposed strategy avoids the engagement of a crowbar circuit by utilizing the PI controllers with modified feed-forward compensators (MFFCs) and series R-L circuit. The series R-L circuit is inserted between the rotor-winding terminals and the ac-side of rotor-side power converter (RSPC) when the rotor overcurrent exceeds its threshold value during faults. Conventionally, the RSPC cannot generate the required excitation voltage due to its small ratings when the DFIG experiences a voltage deficiency following the occurrence of a grid fault. Thus, both the MFFCs and series R-L circuit are implemented to not only correct the conventional feed-forward compensators of the PI controllers for the back-to-back converters but also limit the rotor overcurrent and dc-link overvoltage to within their threshold values. In so doing, the fluctuations seen on the active and reactive powers responses are also automatically restricted, which ensures the smooth transitions. Also, the DFIG’s reactive power control is modified to stably support the point of common coupling (PCC), i.e., DFIG terminal voltage. Comparative studies with five grid-code requirements are performed for a wind farm with 15 WTs to demonstrate the LVRT performances of the proposed scheme and conventional schemes using MATLAB/Simulink software.