The Study On Coordinated Control Strategy Of Doubly Fed Induction Generator For Low Voltage Ride Through

In the development of renewable energy,wind power generation because of the advantages of the large exploitable capacity and cleaning,become the fastest growing energy in the power system.With mass interconnection of wind turbines,the unit off grid problem has emerged.It is a great threat to the safe and stable operation of power grid.To prevent the expansion of grid failure and maintain the stable operation of the power system,national grid company put forward more strict technical requirements for interconnection of wind farm,including low voltage ride through(LVRT),reactive power control and the output power control.Based on doubly fed induction generator(DFIG)as the research object,this paper studies optimization of the low voltage ride through performance of DFIG by using DIgSILENT simulation platform.First,studies the mathematical model,working principle and control method of DFIG.Second,does a detailed theoretical analysis and simulation study on the DFIG transient response under the three phase symmetrical fault.According to the principle of conservation of flux,analyzes the transient characteristics of DFIG stator and rotor flux during voltage drop,and on this basis derive mathematical expressions of DFIG stator current,rotor current,and rotor voltage,quantitative analysis of the relationship between the degree of voltage drop,the output power of DFIG and instantaneous maximum rotor current.Third,studies the DFIG rotor side crowbar protection technology,presents the theoretical foundation for selecting crowbar resistance and proposes two crowbar switching solutions.Comparative analyzes the low voltage ride through performance for different crowbar resistance and switching strategies,verifies the correctness of the setting method of resistance and develops a crowbar switching scheme according to the degree of voltage drop.Last,after expounding power output relationship,this paper studies the element need to be considered for set out DFIG power control strategies during LVRT and elaborates power output limit of the stator side and grid side.Proposes a power coordinated control strategy based on voltage of DFIG low voltage ride through.The simulation result manifests that the improved control strategy can optimize the performance of DFIG and can enhance the transient voltage stability of power grid to a certain extent.