Low Voltage Ride Through Of DFIG-based Wind Turbines And Its Impact On Stability Of Power System

Global energy crisis, environmental pollution and climate change and so on make all countries attach great importance to the use of renewable energy. The proportion of wind power generation in electricity production is increasing, which brings new challenges to the safe and stable operation of power system. It is an important subject of wind power technology to study the interaction between large capacity wind farm and power grid, and the requirementsof power grid for wind powerintegration.In this paper, the mathematical model, the electromagnetic transient analysis theory, the low voltage ride through scheme of the DFIG-based wind turbine and its influence on the small disturbance stability of the power system are studied. As the concise and practical mathematical model is the theoretical basis for solving practical problems, the mathematical model and wind turbine model of wind power generation system is established in this paper which includes the wind turbine model, shaft model and pitch control model. Furthermore, the mathematical model of DFIG in three-phase stationary coordinate system and two-phase arbitrary speed rotating coordinate system is derived. Considering the bigger error and a series of ellipsis and approximate of traditional DFIG transient analysis, this paper accurately calculated the steady components and transient components of the DFIG undergrid symmetrical fault based on the mathematical model of DFIG in two phase stationary coordinate system. A resistance and capacitance Crowbar circuit structure is proposed, the parameters of resistance and capacitance Crowbar circuit are determined and optimize the switching scheme of the Crowbar circuit by using the accurate rotor current expression. For the studies on the low voltage ride through ofDFIG, a simulation model was built in DIgSILENT/PowerFactory. The simulation results show that the proposed Crowbar resistance and capacitance circuit and switching strategy is reasonable, the effect of low voltage ride through is better than the traditional scheme. Finally, a small disturbance stability model of DFIG is established. The impacts of large capacity double fed wind farm on small disturbance stability of the system are analyzed. Eigenvalue results show that the integration of wind farm did not change the original electromechanical oscillation modes of system, but will add a special oscillation mode; in appropriate wind power penetration rate and transmission distance, DFIG-based wind farm can improve damping characteristics of system.