Fault current contribution of DFIG under unsymmetrical fault

In this paper, the transient characteristics of double-fed induction generator (DFIG) are analyzed. Based on this, the fault current contribution of DFIG with and without crowbar are compared. Comparison result shows that fault current of DFIG under different ride-through conditions differs widely from each other. Under unsymmetrical fault, the DFIG with a crowbar is converted to squirrel case induction as a load connected to grid and the positive or negative sequence current is determined by each equivalent circuit. As to the DFIG without a crowbar, negative sequence current is determined by its equivalent circuit and the positive sequence current is adjusted by the excitation system with its output related to the control of DFIG. The methods for calculating fault current contribution of DFIG under these two ride-through conditions are also presented. Then, the negative effect on protection that caused by different DFIG is studied. At the end, a case is set up to verify the accuracy of methods for calculating fault current contribution. The simulation result also shows the difference of DFIG fault current under different ride-through conditions.