Research On Dynamic Equivalent Modeling Of Wind Farms

With the increasing of the capacity and number of large-scale wind farms integration, the fluctuations and intermittent of wind power output will challenge power system security and stability greatly. Theory and method for dynamic equivalent modeling of wind farms has become an urgent basic and applied research project. Firstly, this paper proposes the method for the wind generation system modeling based on operating data, and then for three common wind generation systems, the dynamic equivalent modeling wind farms under wind speed fluctuations and faults are studied respectively. The main contributions of this paper are as follows:(1) A method for the wind generation system modeling is presented based on operating data. According to measured operating data and statistical methods, the measured power curve of wind turbine is obtained and used to set up the mapping relationship between tip-speed ratio and wind power coefficient. Through using look-up table to establish wind turbine model, the wind generation system is obtained. Compared with the measured data, the simulation results show that the model based on proposed method has higher accuracy and engineering value.(2) Based on the analysis of impacts of wake effect and time delay on output characteristics of wind farm and applicability of wind farm common equivalent methods under wind speed fluctuations, a single machine representation method using variable parameters of capacitance compensation is presented for two kinds of reactive power compensation at its terminals, to avoid the reactive power errors from common equivalent modeling methods. This method is suitable for the dynamic equivalent modeling of wind farm containing fixed-speed wind turbines under wind speed fluctuations. The simulation results show that the equivalent method can effectively reduce reactive power error of the equivalent model.(3) Based on the applicability of wind farm common equivalent methods under faults, a multi-machine representation method for dynamic equivalent model of wind farms with fixed-speed wind turbines is presented. Using the wind turbine similar operating point as the grouping rule of wind turbines, the proposed method defines the new cluster classification index. Then the wind turbines are dynamically grouped by clustering algorithm, and the parameters calculating methods, wind farm collector system simplification and simulation modeling process of equivalent model are provided. Compared with the traditional methods, the simulation results show that the multi-machine representation method is effective.(4) A dynamic equivalent modeling of wind farms with doubly-fed induction generator wind turbines under faults is proposed. This method uses the doubly fed induction generator pitch control action as the grouping rule of wind turbines. By extracting eigenvectors that reflect pitch control action, they are used as input of support vector machine (SVM). Then the wind turbines are dynamically grouped. Thus a wind farm model represented by three equivalent wind turbines is obtained. At the same time, the parameters calculating methods of equivalent model are provided. The simulation results show that the proposed three-machine equivalent model can more accurately describe the dynamic characteristics of the wind farm at the grid integration point.(5) According to the fault isolation of double pulse width modulation (PWM) converters for directly driven wind turbine with permanent magnet synchronous generator (PMSG), when the low voltage Ride-through (LVRT) control is neglected, or when the over-dimensioned capacitor is taken as the LVRT control, the wind farm with PMSG can be equivalent into a wind turbine generator, and the parameters calculating methods of equivalent model are provided. The simulation results show that this method is suitable for the dynamic equivalent modeling of wind farm containing directly driven wind turbine with PMSG under wind speed fluctuations and faults.