Transient Stability Mechanism of DFIG Wind farm and Grid-connected Power System

In China, the wind farm is usually with large capacity, centralized, multipoint into the grid and far away from the loading area, which lead to the link between the wind farm and power grid is weak, and the impact of wind power on power system extends from local area to the system stability. Meanwhile, the structure and characteristics of wind turbine generator (WTG) are different from those of conventional generators. A lot of dynamical phenomena can not be explained by the existing theory. So it is very urgent to study the impact of large-scale wind farm on power system transient stability. At present, power system transient stability including large-scale wind farm is investigated generally by building wind farm model, simulating and drawing conclusion. But the stability theory of power system including WTG is still insufficient. In the paper, firstly, from the view of torque balance, the operating-point and variation of rotor speed are used to analyze the transient stability of wind farm consisted of Double Fed Induction Generator (DFIG). Secondly, the active power and mechanical power of wind farm is equivalently converted to the mechanical power of synchronous generator, then the extended equal area criterion of power system including wind farm is derived. Thirdly, the mechanism of wind farm effect on power system transient stability is analyzed, and the impact of wind turbine control characteristics on the equivalent mechanical power of synchronous generator is also considered. Finally, a modified CIGRE B4-39 test system is adopted to verify the correctness of the proposed method.