Short circuit current analysis of DFIG-type WG with crowbar protection under grid faults

For doubly fed induction generator (DFIG) based wind power systems, rotor crowbar is a commonly used protection method against rotor surge current during low voltage ride-through (LVRT) periods. One of the basic problems is the rotor surge current characteristic analysis of DFIG, the other is the investigation of effective crowbar circuit and appropriate control methods. Based on the detailed analysis of the complete stator and rotor flux response of DFIG after crowbar fired, a time domain analytical expression of the short circuit current of DFIG applied to (a) symmetrical grid faults is proposed. In order to improve the stator terminal power characteristic of DFIG during crowbar fired, a novel crowbar consisting of resistance in series with capacitor is proposed, and the capacitor value selection method is also given. A typical 1.5 MW DFIG wind energy conversion system is used for case study. The analysis and simulation results validate the accuracy of the analytical expression of the short circuit current and the effectiveness of the proposed novel crowbar.