Study On Characteristics Of Wind Turbine And Short Circuit Current Limitation Under Power Grid Fault

With the rapid development of renewable energy,the capacity of distributed generation is increased.When the short-circuit fault occurs in power grid,the operation status of grid-connected distributed power supply and its impact on short-circuit current capacity of power grid need to be studied.As the scale of power grid is increasing and the structure is becoming more and more complex,and the short-circuit limitation is also an urgent problem to be solved.Firstly,based on the mathematical models of different types of wind turbines,the influence of different types of wind turbines on the short-circuit capacity of the system is studied.In this paper,the short-circuit current mathematical expressions of FSIG,DFIG and PMSG are calculated.In addition,the action of Crowbar protection circuit in DFIG and unloading circuit in PMSG is considered,a typical distribution network model is established to simulate different types of wind tuebines in the distribution network under short-circuit conditions.The output current of different types of wind tuebines and their influence on short-circuit capacity of the system are obtained.It provides a reference for the selection of grid-connected points of wind turbines and the planning of distribution network with distributed generations.Secondly,this paper studies the system characteristics of DFIG at different voltage sags,a double resistance braking method based on fuzzy control switching is proposed.Based on the mathematical model of DFIG,it analyzes the function of series dynamical braking resistor(SDBR)theoretically.The series impedance value of SDBR is determined by the variation of the rotor open circuit voltage,the voltage and current of the stator and the rotor,the heat capacity of SDBR also be considered.A double series resistors braking mode of SDBR is proposed.Through adopting the fuzzy control strategy,it implements the double series resistors switching,so as to improve the LVRT performance of DFIG.Finally,the problem of short-circuit current in local areas of Anhui power grid is studied,and the short-circuit current level of Hefei power grid under different current limiting modes is calculated.The advantages of FCL in short-circuit current limitation of Anhui power grid are analyzed.Based on this,a fault current limiter based on Pulse Width Modulation(PWM)control is studied,which uses the high frequency characteristics of the PWM controller to suppress the low-order harmonics.Based on the analysis of its principle,aiming at the problem of over-high short-circuit current of 220 kV Feixi bus in Hefei power grid of Anhui Province in 2020,according to the current limiting effect of different installation positions of FCL in power grid,the best installation scheme is obtained.According to the scheme,a simulation with FCL is carried out in the equivalent system of Feixi local power grid to verify the current limiting effect of the fault current limiter.