Research On Short-circuit Current Characterstics Of DFIG-Based Wind Farm Considering The Interaction Influence Of Wind Turbines

Doubly-fed wind turbine is characterized by high efficiency, fast dynamic response and so on. It has been the primary choice of wind farm in our Country. However, the transient characteristics of doubly-fed wind turbine have great differences with traditional synchronous generator. So getting the electric power transient signal of the doubly-fed induction generators is helpful for relay protection setting and the electrical equipment selection and so on. At present, the study on the short-circuit current of the doubly-fed wind turbine has mainly focused on the single unit and has not come into being a unitive method in transient analysis. The influences of wind turbine interaction in wind farm on the short-circuit have not been studied clearly, so it is necessary to research on the short-circuit current of the wind farm when considering the influences of wind turbine interaction. The main study process and production are as follows:In the case of single doubly-fed wind turbine, unlike the previous study, this paper will build a transient-state transmissibility function model of doubly-fed wind turbine for transient calculation in both cases of severe fault(in which crowbar protection is assumed activated) and non-severe fault(in which rotor is assumed governed by converters). The model reveal the producing principle of the short-circuit current components and the transitive relation of each excitation source.Base on the transient-state transmissibility function model of doubly-fed wind turbine, stator short-circuit current and stator short-circuit current of doubly-fed wind turbine have been calculated in both cases of severe fault(in which crowbar protection is assumed activated) and non-severe fault(in which rotor is assumed governed by converters). In the process of calculation, flux linkage and stator short-circuit considered to be a closed-loop transfer relationship. With less simplification to the transfer relationship in system parameters and structures in order to guarantee accuracy for transient calculation. The digital simulation verified the accuracy of the current formula. The current formula can reveal the influence rule of the inner loop controller cut-off frequency to the rotor current and rotor current.Build the equivalent circuit of doubly-fed wind turbine based wind farm under grid fault, the incremental of short-circuit current formulea have been derived Incremental. This paper finds out the relationship between the incremental of short-circuit current of unit doubly-fed wind turbine and numbers of doubly-fed wind turbine, system impedance, parameters of doubly-fed wind turbine based wind farm, parameters of doubly-fed wind turbine. The digital simulation verified change rule of wind farm short-circuit current when considering the influences of wind turbine interaction. Then calculate the short-circuit current of wind farm based on the equivalent circuit. The simulation has proved its accuracy.In this paper, the research work further perfects the short circuit analysis of both single set of doubly-fed wind turbine and doubly-fed wind turbine based wind farm, the research work offers a new method for fault caculation of doubly-fed wind turbine. This paper provide technical support for fault caculation of doubly-fed wind turbine based wind farm and relay protection setting.