Research On Low/High Voltage Ride Through Transient Characteristics Of Doubly-fed Induction Generator

With the increasing penetration of wind power in the power grid,doubly fed induction generator(DFIG)is the main model of wind power generation,and its safe and stable operation is particularly important for the stability of the power system.DFIG is particularly sensitive to the change of grid voltage and the influence of wind power fluctuation and randomness,which makes it difficult for DFIG to realize fault ride through.Therefore,it is of great significance to study the LVRT and HVRT of DFIG.The main research work of this paper is as follows:(1)The mathematical model of doubly fed induction generator(DFIG)is established,and the transient characteristics of DFIG with crowba r protection are analyzed.According to the fault characteristics and crowbar protection action,the whole process of grid voltage fault is divided into three stages.The first stage is fault occurrence and stator voltage drop,but crowbar protection has n ot been put into operation;the second stage is after a short delay At the same time,the converter on the rotor side is blocked,and the dynamic response after grid voltage recovery is regarded as the third stage.The influence of crowbar protection input delay on DFIG transient performance is simulated and analyzed,and the correctness of theoretical derivation is verified.(2)This paper analyzes the transient process of stator and rotor flux linkage of DFIG under symmetrical and unsymmetrical voltage surge faults,and the existence of negative sequence component makes the flux linkage double power frequency oscillation.On this basis,the transient current expressions of stator and rotor of DFIG are derived,and the fault current characteristics of DFIG are studied.Compared with the time-domain simulation results,the simulation waveforms are in good agreement with the theoretical waveforms.(3)The transient process of stator flux linkage under different voltage surge modes is studied,the expressions of stator flux linkage under different voltage surge modes are derived,and the factors affecting the transient characteristics of stator flux linkage are compared and analyzed.The transient characteristics and attenuation components of stator flux linkage are different with different rising modes of grid voltage.The condition of minimizing the transient attenuation component of stator flux linkage is proposed.