Research on Low Voltage Ride Through Capability of DFIG Based on Adaptive Crowbar Resistor

Abstract

Crowbar circuit is the main means to achieve low voltage ride through (LVRT) in DFIG (doubly-fed induction generator). The fixed crowbar resistor is usually adopted in traditional crowbar circuit, which is difficult to meet the requirements of grid interconnection criterion for dynamic reactive power in the wind farm. This paper starts with the DFIG mathematical model with crowbar circuit. According to the analysis of the working state of the generator when the power grid is faulty, the analytical formula of the rotor current for the grid fault is obtained. Based on this, a self-adaptive crowbar control strategy is proposed. The adaptive crowbar resistance was set two times on the basis of limiting the rotor current. Then the theory of adaptive control strategy was verified by theoretical analysis and simulation experiments. The results show that the adaptive resistor control strategy combined with hardware and software increased the reactive power by about 0.9Mvar within 0.ls after grid fault occurs, which has a significant effect on optimizing the reactive power output of the DFIG's stator winding. And this adaptive resistor control strategy effectively improves its LVRT capability.