Transient Stability Analysis Of Power System Integrated With DFIG Wind Generator

Doubly-fed induction generator(DFIG)has become a research hotspot in the field of wind power because of its mature technology and wide application.Based on the mathematical equation of the model,the single-generator grid-connected system and the three-machines-nine-bus grid-connected system of doubly-fed induction generator are modeled and simulated,and the transient responses of the two systems under wind speed disturbance and three-phase grid-connected fault disturbance are studied.Firstly,the mathematical model of DFIG system is established.The switching model and average model of converter are analyzed mathematically,and a general mathematical model is established.Secondly,a simulation model is built in Matlab/Simulink.By comparing the steady-state simulation curves of the converter switching model and the average model,the feasibility of using the average model instead of the switch model is verified.Then,the dynamic response of the two systems under disturbance is simulated and analyzed by time domain simulation method.The main disturbances are wind speed fluctuation and three-phase grounding fault.For a single-machine system,firstly,wind speed drop simulation is carried out to study the dynamic response of the system and realize the maximum power point tracking(MPPT)of the system.Secondly,based on the analysis and study of the mathematical model,a comprehensive low voltage ride through(LVRT)based on the series dynamic resistances(SDR)of the rotor side is proposed,and the simulation of three-phase drop fault on grid side is carried out.For grid-connected three-machines-nine-bus system,firstly,wind speed fluctuation is simulated,and the influence of different inertia of doubly-fed induction generator on system transient response is analyzed.Secondly,the effects of different grid-connected capacities and different fault points on the transient stability of power angle between synchronous generators are analyzed.The results of the example in this paper show that the large moment inertia of wind power system has strong resistance to wind speed fluctuation.In the scenario of three-phase ground fault,the critical clearing time(CCT)of the power system in the example of the 25 MW wind power grid is reduced.The other examples show that the wind power grid connection can extend the critical clearing time of the power system and the extension time is related to the grid-connected capacity.In the case of the same grid-connected capacity,the closer the fault is to the grid-connected point of wind power,the greater the impact of the critical clearing time.