New method of setting the maximum crowbar resistance for doubly-fed induction generators under grid faults

In present doubly-fed induction generator (DFIG) wind turbines are widely remain connected to the grid network during faults, so-called Fault ride through (FRT). A crowbar is generally used in the rotor circuit protection which will help to support the FRT capability of the DFIG. In this paper, the behaviors of the DFIG system under three-phase faults influenced by the value of crowbar resistors are investigated in the Matab environment. The simulation results show that rotor current rise is up to 4.5 pu in case of without crowbar protection, while the peak values of rotor currents have been reduced to 2 pu after using the crowbar resistance value at least 30 times of rotor resistance. The new method of setting the maximum crowbar resistance is proposed. The maximum value of crowbar resistance should be limited at 70 times of rotor resistance in order to protect the over-voltage of rotor side converter from high rotor currents, and also avoid high currents flowing through the rotor side converter to DC-link capacitor.