Based On The Equivalent Model Of DFIG Utilizing SSSC To Improve The Transient Stability Of Wind-thermal Bundled System

Wind-thermal bundled system is a mode realizing transmitting wind power and thermal power on a large scale,and there are many advantages to this transmission e.g.: restraining the fluctuation of wind power,improving use ratio of making full use of transmission channels and reducing the power price.However this mode also brings some negative effects to the power grid.The power grid characteristics are complicated due to the close proximity of wind power and thermal power coupling.In addition,the external transmission power of wind-thermal bundled system is generally large,and the risk of instability is relatively large.Therefore,it is of great significance to analyze and study the transient stability of wind-thermal bundled system.In this thesis,the stability of wind-thermal bundled system is discussed and the transient stability of the system is improved by using Static synchronous series compensator(SSSC).The structure principle,mathematical model and control system of DFIG are described in detail,and the control strategy of PWM converter of DFIG is analyzed.On the basis of vector control technology,it is illustrated that the decoupling of active power and reactive power is implemented by rotor side converter and the reactive power exchange to power grid is realized by the network side converter.In Matlab/Simulink,the steady state power output of DFIG is verified.Based on the power decoupling and fault crossing characteristics of the DFIG,the transient behavior of the DFIG is analyzed,and the external equivalent model of the DFIG is given in different situations.The power change of the wind generator is simulated and analyzed,and the numerical value is given by taking 9WM wind farm as an example to verify the rationality of the external equivalent model of the wind generator.Provides a simplified model for follow up research.It is crucial for studying transient stability of the system that studying the transient stability affected by the synchronous unit in the system through discussing that DFIG has no question of transient stability and has no embodiment of the characteristic of rotational inertia.Based on the different equivalent models of the wind turbine before and after the fault,the power characteristics equation of the synchronous unit in the wind-thermal bundled system was deduced,and the influence of DFIG on the transient stability of the wind-thermal bundled system was analyzed in detail based on the equal-area rule.A simulation model was established to analyze and compare the transient stability of the wind-thermal bundled system and the traditional thermal power system,and the transient stability of the wind-thermal bundled system under different proportions of wind-thermal.On the base of expounding the basic principle,mathematical model and control mode of SSSC,the mechanism of SSSC to improve the transient stability of wind-thermal system is analyzed in theory.A double closed-loop control strategy of SSSC was designed for wind-thermal bundled system.Through simulation analysis,it is concluded that SSSC can effectively improve the transient stability of wind-thermal bundled system.