Power Angle Characteristic Research Based On DFIG Wind Farm

Under the dire circumstances of global energy crisis and environmental deterioration,wind power as one of the best clean energy,has aroused extensive attention all over the world.As the wind power penetration increases,the wind farm uninterrupted operation capacit y requirement by the power grid has gradually increased,and the stability of the power syste m containing wind farm has become the focus of the current research.When the grid voltage sag due to fault or other reasons,if the wind turbine cannot keep connecting with the system,it would likely cause the voltage further drop,and power deficiency due to wind farm disconnection would likely lead to collapse of frequency,and it brings great challenge to the normal operation of power system.Therefore,it has important significance for the safe and stable operation of the grid to improve the low voltage ride-through capability.According to the working principle and control strategy of DFIG(doubly fed induction generator)wind turbine,simulation model of single DFIG wind turbine on the PSCAD/EMTDC platform was putted up to achieve the purpose of the maximum wind energy tracking and decoupling control of active power and reactive power.The output characteristic of the normal operation and external fault of wind turbine was analyzed to verify the correctness of the model.The equivalent equation of doubly fed wind power generat ion was deduced,and the stator rotor flux linkage angle was set as the power angle of doubly fed wind power generator through quantitative calculation and analysis.The terminal voltage sag reasons of DFIG single machine infinite bus system were analyzed during the fault,and the power angle control strategy and DFIG low voltage ride-through scheme was established during the fault accordingly.The calculation method of equivalent accuracy o f doubly fed wind farm was proposed,and the wind farm equivalent effect could be quantitative calculated based on the numerical evaluation,trend evaluation and weight which was calculated by fuzzy analytic hierarchy(AHP)method.The DFIG wind farm equivalentmodel of 33 units was putted up with the low voltage scheme based on power angle control strategy,and the results verified that this scheme could improve the parallel point voltage of the wind farm effectively,could send out more active power and reactive power during the fault,could help the system recovery and improve the transient stability of power system.