Fault Characteristics Analysis And Protection Strategy Study Of Wind Farm Parallel Operation

With the rapid development of wind power generation technology,the capacity of wind power grid connected to the grid is increasing,As the main model of the current wind farm,the transient characteristics of the DFIG are very different from that of the traditional generators.It has a great influence on the traditional relay protection configuration and setting calculation,It poses a certain threat to the safe and stable operation of the current large power grid.Therefore,it is necessary to further study the transient characteristics of DFIG,and improve the current relay protection configuration plan according to its transient characteristics.This paper starts with the basic mathematical model of the DFIG,Equivalent circui t of DFIG when the power grid fails,The calculation method of the equivalent electromotive force is derived,and the expression of the short circuit current is further obtained.On this basis,the fault characteristics and the influence of the fault characteristics on the traditional relay protection are analyzed.After analyzing the applicability of traditional protection,the protection scheme for wind farm converge line is put forward.In this paper,the mathematical model of DFIG is analyzed.The equivalen t mathematical model of DFIG in three-phase stationary coordinate system and two-phase rotating coordinate system is mainly explained,and the coordinate transformation method between two coordinate systems is expounded.The operation principle of DFIG and the control strategy of DFIG in steady-state operation and fault transient stage are analyzed,and the equivalent model of DFIG is verified by simulation software.Second,when the power grid fails,we give full consideration to the crowbar resistance and fault control strategy of DFIG,.Starting from the basic mathematical relationship of DFIG,The equivalent circuit of DFIG is deduced and it is similar with conventional generators including electromotive force and impedance.Based on the transient mathematic al model of DFIG,The expression of the equivalent EMF of DFIG is derived and its characteristics are analyzed,The validity of the equivalent electromotive force and the equivalent circuit is verified by the simulation.Based on the transient characteristics of DFIG,the non power frequency characteristics and the weak power characteristics of the doubly fed wind turbine are analyzed.The effects of the non power frequency characteristics,the weak power supply characteristics and the low voltage crossing requirements on the relay protection setting calculation are explained.Through the analysis of the applicability of the traditional protection,it is shown that the longitudinal differential protection and the three stage current protection still have some pr acticability.On the basis of economy and practicality,this paper gives a scheme of relay protection configuration and setting method suitable for the converge line of wind farm.After the large-scale wind farms are connected to the network,this paper provides an economical and practical scheme for the relay protection of the wind farm confluence line.