| On the background of energy exhausting and environment worsening, as one of the most value clean and renewable energy, wind power has obtained great development in recent 20 years. But as increasing of the wind turbine installed capacity, the randomness and intermittent of wind farm will make more and more influence for grid. Thus, for the power system that contain large wind farms, need to build a more precise mathematical model of wind farm to make simulation analysis. This paper propose a new way to model wind farm based on coherency equivalent, which has great theoretical significance and practical value.The domestic and international research status on network equivalence is summarized in this paper, on this basis, main tasks are as follows:(1) This paper will study doubly fed induction generator (DFIG) working principle and establish its detailed mathematical model, which including wind turbine aerodynamic model, transmission system model, induction generator model and its inverter control system model.(2) According to the terrain and wind turbines'distribution, the wind farms are divided into two categories, and design suitable method of coherency identification for them separately. Specifically, this paper propose a coherency identification method based on markov chain for complex terrain or distribution irregular wind farm.the equivalent calculation method of equivalent electric parameters and equivalent wind velocity will be provided later.(3) Validate the effectiveness of equivalent method proposed this paper by using measured data of an actual wind farm.(4) We build a large grid simulation system based on the PSS/E that contain large wind power, by which we try to find the different between traditional single machine equivalent and coherency equivalent proposed by this paper and analyse the differences. Simulation results show that coherency equivalent modeling menthod of wind farm more precise than traditional single equivalent modeling methods for wind farm.
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