Evaluation and analysis of transient current of a DFIG windgeneration system under grid fault

In order to analyze effectively the operational capability of the low voltage ride through(LVRT)of a gird-connected wind turbine with doubly fed induction generator(DFIG),it is necessary to evaluate directly the transient currents of a DFIG wind generation system under a grid fault.By using the transient principle of the stator and rotor flux of a DFIG,the expressions of the stator and rotor transient currents of the DFIG wind generation system are derived under both the terminal short-circuit fault and the different grid voltage drop faults.By considering the drive train flexibility of a DFIG wind generation system,the proposed expressions of evaluated transient currents are validated by the time-domain simulation results from the transient models.In addition,by using the presented expressions,the maximum values of the stator and rotor transient currents are calculated under the different initial conditions of the output active power,reactive power and the different grid voltage drop.The effects of transient performances of the DFIG wind generation system on the different initial operational conditions are obtained.