Study On The Engineering Method For Short Circuit Current Calculation Of Wind Turbine

As the number of wind turbines connected to the grid is steadily increasing, attention should be paid on the short-circuit current calculation of wind turbines for the protection configuration and the computation procedure of power system. The Doubly-fed Induction Generator (DFIG), which has features of variable speed operation, superior steady-state and transient-state operation characteristics and relatively small excitation rating, is especially suitable for the wind power generation.Firstly, the principle of the DFIG was studied in this thesis. According to the physical character of the wind turbine, the models of DFIG then were made. The models could represent the dynamic characteristics of the VSCF wind turbines.Based on the basic voltage and flux equations of the Doubly Fed Induction Generator, this paper derived expressions of short-circuit current of wind turbines, which are expressed by transient equations of stator and rotor flux. The transient equations of stator and rotor flux were functions of initial values of stator and rotor flux and transient time constants of stator and rotor windings. The initial value of stator flux was calculated, considering the influence of stator resistance, and the rotor flux equation under steady state condition was used to calculate the initial value of rotor flux. Transient behaviors of the stator and rotor flux were analyzed when three-phase faults occurred at terminals of generators, then the transient equations of stator and rotor flux and detailed equations of the short-circuit current of DFIG could be obtained.This thesis chose the Capacity-weighted method to obtain the equivalent model of the wind farm. In different operation mode, the equivalent models were compared with the detailed models. Simulation results showed that the equivalent model had a high accuracy, which can meet the need of engineering calculations.DIgSILENT/PowerFactory program was used to execute electromagnetic transient simulations when three-phase faults occurred at terminals of generators and at the power system respectively. Simulation results show that it is efficiently to use the equations of short-circuit current proposed by this paper to calculate the short-circuit current of DFIG.