The Study Of The Grid Fault Characteristics And Protection Strategy With Double-fed Wind Power

Mechanism of wind power and conventional thermal power is different, great changes have taken place after fault electromagnetic transient characteristic. The doubly-fed wind power’s access, making the grid structure more complicated, the reliability and security is difficult to get effective guarantee. Therefore, this article considers the doubly-fed wind power generator electromagnetic transient characteristic research under the symmetric and asymmetric fault of the grid. And get the doubly-fed rotor and stator current under the power grid fault transient expression; and is verified by PSCAD simulation. At the same time, considering the large scale doubly-fed wind power system to the influence of the traditional protection in the power grid, proposed in view of the wind farm bus lines and improve the protection strategy, send line of wind farms and verified the effect under the grid fault with the PSCAD simulation.This paper established the doubly-fed generator system transient mathematical model under different coordinate system, expounds the synchronous rotating under the transient model of doubly-fed induction motor and the commonly used coordinate transformation; which was deduced the mathematical model of DFIG line-side and rotor side converter, analyzes the characteristics of doubly-fed induction wind generator power generation and operation principle, and builds the PSCAD model of DFIG simulation validation.Secondly, based on the symmetric and asymmetric fault of the grid, fully considering the voltage’s phase jump of the DFIG machine, DFIG rotor side and network side converter control and DC bus voltage fluctuation of the influence of the fault current. Transient mathematical model is deduced respectively using the DFIG under symmetric and asymmetric fault DFIG can reflect the transient output characteristic of DFIG rotor current time-domain expressions and through the PSCAD simulation and dynamic model experiment to prove the validity of the formula, and analyzes DFIG machine at a jump, and doubly-fed fan network side and rotor side converter control mechanism and the influence degree of fault current.Due to weak power and fault characteristics of doubly-fed wind power itself, when wind power bus line or send line failure occurs, the traditional protection is not reliable. In this paper, based on the fault characteristics of doubly-fed we proposed wind power bus line adaptive current protection strategy, based on the wind of the steady state of out line current longitudinal differential protection strategy and adaptive distance protection strategy. And building containing doubly-fed wind farms and grid tie line of PSCAD model respectively to protect and improve the traditional protection strategy for simulation and analysis. For large-scale doubly-fed wind farms connected to the power grid when bus line and out of line protection theoretical basis is provided for the research and application of new principle.