| With the increasing demand for new energy,the installed scale of wind power is becoming larger and larger,and the impact on the power system can not be ignored.It is important to study the equivalent method of wind power field for power system operation state analysis.Based on the detailed mathematical model of wind farm,the accuracy of describing the characteristics of wind farm by single machine equivalent model is analyzed theoretically and simulated,and the causes of the errors are given.Through theoretical and simulation analysis,it is concluded that the difference of operation state between wind turbines and the difference of parameters of wind turbines in wind farms can lead to the inaccuracy of the equivalent model,and the bigger the difference of operation state and parameters,the bigger the error.When the operation states and parameters of wind turbines are the same in wind farms,the characteristics of wind farms can be accurately described by using single-machine equivalent model,including capacity weighting method and its improved capacity weighting method.According to the conclusion that accurate equivalence can be achieved when the parameters and operation state of wind turbine are the same,a new method is proposed to divide a wind turbine into several units and then establish the equivalent model of a single wind turbine in a wind farm.The input power of separated wind turbines is the same.The determination of equivalent wind turbine parameters takes into account the actual input power of the unit.Using this parameter to describe the equivalent wind turbine,the input impedance of the wind farm before and after the equivalent value can be guaranteed to be consistent.Taking SCIG as an example,the simulation analysis is carried out.The simulation results show that the single-machine equivalent model established by the proposed parameter determination method can describe the characteristics of wind farm well.Based on the method of determining the equivalent parameters of a single generator,in order to further improve the accuracy of the equivalent model of a wind farm,a twogenerator equivalent model of a wind farm and a method of determining its parameters are proposed.Among them,the input power of one equivalent wind turbine is the sum of wind power of wind farm,while the input power of another equivalent wind turbine is zero.The proposed two-generator equivalent model can ensure that the input impedance of the wind farm and the kinetic energy stored in the wind farm are consistent before and after the equivalent.Taking SCIG as an example,the simulation analysis is carried out.The simulation results show that the proposed two-machine equivalent model is more accurate than the single-machine equivalent model in describing the characteristics of wind farms.Through the simulation analysis of the system fault and the change of input wind power,it can be seen that the proposed wind farm equivalent machine models have good equivalent accuracy and adaptability. |
