Transient Characteristics Research Of DFIG Wind Turbine Under Power Grid Failure

With the deepening of energy crisis and people’s concern for environmental issues, wind power presents a rapid growth trend in the countries of the world. Characteristics of the development of wind power in China are large-scale centralized network, and double-fed induction wind generator (DFIG) is the most widely used in wind farms. The structure of doubly fed induction generator is different from the traditional synchronous and asynchronous motors. The research of transient characteristics and fault mechanism is not deep enough, has not yet formed a mature failure analysis methods and mathematical calculation model. This makes the relay setting calculation difficulties, threats seriously electrical equipment safety and affects the safe and stable operation of the grid.Firstly, this paper analyzes the principle and mathematical model of a typical directional vector control strategy of doubly-fed machine. In Matlab/Simulink software, the simulation model containing the mechanical parts, electrical parts and control part is built and model in steady state and fault cases of operating characteristics are analyzed, verifying the feasibility of the model. Secondly, this paper established a space vector model and the positive sequence and the negative sequence model of the doubly fed induction generator. Researching the steady-state relationship between the doubly fed induction generator rotor voltage amplitude and phase angle of the stator voltage and current, the double fed induction wind generator terminal voltage drop physical mechanism of the motor internal electromagnetic transient process is analyzed. Then, using the method of superposition of steady-state and fault based DFIG space vector model, the grid occurred the symmetric and asymmetric voltage drop, the analytic expression of short-circuit current of the DFIG stator and rotor side is derived in detail.The network happen symmetric and asymmetric fault, Crowbar circuit input in the stator and rotor of short-circuit current calculation model, established the unit is equipped with a low voltage ride through capability and further extend the grid into Crowbar circuit stator and rotor short-circuit current calculation model, analysis of the short-circuit current the frequency components, the proportion of the size of the mechanism. Finally, using of the resulting fault current model, analyzing some factors such as the short-circuit time plant operation conditions, the structural parameters of the unit itself, the voltage drop on the influence of the short-circuit current. Both the time-domain simulation model methods and the field test verify the correctness of the expression.In this paper DFIG failure mechanism and transient characteristics are more in-depth study in the grid failure, based on simulation analysis calculation method extends in the direction of further failure mechanism and failure calculation method. The fault characteristic of DFIG from the power grid symmetrical fault to asymmetric fault areas expands on, the proposed calculation method for the failure of the doubly-fed machine has clear physical meaning, more accurate results. And provide a theoretical support for the applicability of current relay Relay principle in the study of large-scale wind power grid.