Transient behavior representation, contribution to fault current assessment, and transient response improvement in DFIG-based wind turbines assisted with crowbar hardware

Abstract

This paper analytically deals with the transient behavior evaluation and crowbar hardware design for the low voltage ride-through (LVRT) capability enhancement in doubly fed induction generator (DFIG)-based wind turbines (WTs). The paper indeed answers the following question analytically. “What are the main criteria for choosing the crowbar resistance?” It is shown that the value of the crowbar resistance affects both the peak values and oscillations of the DFIG transient response. Therefore, the paper first analytically investigates the rotor dynamics with the crowbar hardware during the voltage dip, and then develops analytical expressions for the crowbar resistance design to meet the LVRT requirement. It is shown that selection of the crowbar resistance higher than the maximum value may deteriorate the DFIG LVRT performance. Next, contribution of the DFIG to the fault current by using the crowbar is analytically studied. Then, the impact of crowbar resistance on the damping of the DFIG transient oscillations is examined by the modal analysis and phase plots of the stator flux. At the end, the concept of rotor active impedance is introduced, the LVRT capability of the DFIG is evaluated, and the DFIG transient responses under different crowbar resistances are investigated and compared.