Simulation research for LVRT of DFIG based on rotor active crowbar protection

Aiming at the problems which were brought by wind power integration, it is important to enhance the low voltage ride-through (LVRT) performance of wind turbines in order to ensure the safe and reliable operation of the power system. For the doubly-fed induction generator (DFIG) based wind turbines, crowbar is a commonly used protection method to implement the LVRT capability. Based on analyzing the electric characteristic of the stator and rotor currents during the grid voltage dips in wind turbines with or without crowbar switching, the equation to estimate maximal faulty currents of stator and rotor with crowbar switching is derived. Then a crowbar resistance design method based on the faulty rotor current and the DC-link voltage was proposed, and the specific LVRT control strategy was discussed in this paper. The crowbar resistance can limit rotor fault current, DC-link over-voltage and protect rotor converter effectively during the grid voltage dip. At the same time, reactive power can be fed to the grid through both stator and grid-side converter. A typical 2MW DFIG system was used, the analysis and simulation results show that, with the help of appropriate protective resistor and the reasonable control strategy, the additional crowbar device can effectively help wind generator provide LVRT capability.