Utilizing the direct current (DC) dump circuit (Chopper) on DC-link to protect the rotor side converter (RSC) is commonly done for improving the low-voltage ride through (LVRT) capability of doubly-fed induction generator (DFIG)-based wind turbines. The insertion of Chopper protection will have a greater impact on the short-circuit current characteristics of DFIG-based wind turbines

however present research on DFIG-based wind turbines fault current features under symmetrical short-circuit is primarily conducted on the assumption that the Crowbar acts after fault inception

whereas

the short-circuit current characteristics of DFIG-based wind turbines under Chopper action is rarely studied

making it difficult to analyze the reliability of protection action and equipment safety under its impact in power systems. According to the analysis on the short circuit current of DFIG-based wind turbines unit after Crowbar operates

i.e. the rotor circuit is in series with a resistor

the rotor current loop after fault under Chopper action is analyzed

the blocked RSC and Chopper are equivalent to a variable resistance

the variation of the equivalent resistor along with the voltage drop and running slip is also analyzed. According to the relationship between the DFIG flux and voltage after symmetrical fault

a current analytical expression is obtained for DFIG-based wind turbines under Chopper action by mathematical analysis methods. Finally a simulation model for DFIG-based wind turbines with Chopper protection in MATLAB/Simulink is built to verify the validity of the proposed method.