Research On Equivalence Modeling Method Of Wind Farm Considering The Influence Of Control Strategy

In recent years,new energy power generation has been vigorously developed due to its renewable,clean and pollution-free characteristics,and it is an effective means to solve the problem of shortage of traditional fossil energy supply and pollution prevention.Among them,wind power has developed the fastest due to its clean and efficient characteristics and cost advantages.As the penetration rate of wind power continues to increase,the impact of a large number of connected wind turbines on the power grid has become increasingly prominent,bringing a series of new challenges to the regulation and operation of the power grid.At this stage,cluster development and centralized grid connection are the main forms of wind power development.How to perform equivalence modeling of large-scale wind farms in power system analysis and calculation,taking into account the requirements of calculation efficiency and accuracy,has become a problem of concern.This paper selects the most widely used DFIG wind turbines and PMSG wind turbines as the research objects,analyzes the structural characteristics,advantages and disadvantages of the two types of wind turbines respectively;established mathematical models in three-phase natural coordinate system and two-phase rotating coordinate system;establishes two kinds of converter control strategies;laid the foundation for the subsequent research on the equivalence modeling method of wind farms.A wind farm equivalent modeling method based on output power time series clustering is proposed.This method uses the time series of active power output by each wind turbine in the wind farm to classify,so that the obtained wind farm equivalent model can be applied to the selected certain time period.Dynamic Time Warping(DTW)algorithm is used to evaluate the similarity of operating status,and DBSCAN algorithm is used for clustering.There is no need to specify the number of clusters,ensuring the moderate and effective number of equivalenct machines in the model,and avoiding the errors that may be caused by manual selection.The simulation of the case in MATLAB/Simulink verifies the accuracy and applicability of the equivalence modeling method,and can separate the wind turbines operating in abnormal conditions from the clusters in the wind farm and then perform equivalence separately,thereby it can improve the accuracy of the equivalent model effectively.The equivalence modeling method of a hybrid wind farm composed of DFIG wind turbines and PMSG wind turbines is studied.Based on the analysis of the fault characteristics of the two types of wind turbines when they encounter a grid fault,this paper studies a corresponding low voltage ride through(LVRT)hierarchical control strategy to enable the wind turbines to provide as much dynamic reactive power as possible to support the grid voltage recovery during the failure stage.According to the different control strategies adopted by the wind turbines,an equivalence modeling method for hybrid wind farms is proposed.The analysis of the calculation example verifies the effectiveness of the low voltage ride-through hierarchical control strategy in supporting the grid voltage recovery in the case of a three-phase short-circuit fault,and demonstrates the effectiveness of the equivalence modeling method for hybrid wind farms.