Research On Low Voltage Ride Through Technology Of Doubiy-fed Wind Power Generation System Based On Stator Crowbar Circuit

Wind power installed capacity and power generation in the proportion of the entire power system is increasing.The stator side of the doubly fed wind power generator is directly connected with the power grid,the rotor side is connected with the power grid through a small capacity converter,this kind of special topology causes the doubly fed wind turbine to have more complex transient characteristics during the voltage sag,the stator winding and rotor winding appear large current,DC bus voltage swell,a threat to the safe operation of the converter and caused double fed wind turbine off grid operation.This paper mainly studies the stator Crowbar circuit of the low voltage ride through technology.Firstly,the basic composition and operating principle of the doubly fed wind power generation system are analyzed.Combined with the basic operating principle,the transient response of doubly fed wind turbine is analyzed under symmetrical drop failure of grid voltage.The analytical solution of the rotor fault current is given,when grid voltage symmetrical drop,stator rotor winding parameters,machine terminal voltage drop depth,slip rate and the rotor side of the converter output voltage and other factors affect the rotor fault current size;Using the program of the stator Crowbar circuit mode switching,analysis the rotor transient current response characteristics of the doubly fed wind turbine generator mode switching process.During the grid failure,the stator Crowbar circuit is connected to system,double-fed wind turbine switch to the induction generator mode,the active power and reactive power of system can be controlled by both sides of the converter,effectively suppressing the rotor transient current and DC bus voltage fluctuations and the injection of reactive power contribute to the recovery of grid voltage;Considering the existence of unbalanced torque in the system during the fault,the calculation method of the critical impedance of stator Crowbar circuit is clarified.The relationship between electromagnetic torque,rotor speed and stator Crowbar circuit impedance is analyzed in detail.At the same time,a control strategy of tracking the stator current change is given in combination with the control strategy of the rotor-side converter.The simulation results show that the improved scheme can effectively improve the low voltage ride through capability of the wind power generation system.