Research On Dynamic Equivalence Of Small And Medium Hydropower Generator Group In Interconected Systems

China has a vast territory,wide range of rivers and a large number of tributaries.Therefore,a large number of hydroelectric power stations have been built in the rich areas of water resources.With the rapid development of hydropower energy distribution power generation technology,as well as the rapid development of modern large-scale power grid,numerous small and medium hydropower groups distributed in the system have considerable effect on the stability of power grid system not only in the simulation but also in the actual system.The negative load model is the common model to equivalent the hydropower groups.However,this model structure is simple and hard to reflect the dynamic characteristics of the system under various faults.Therefore,a method for dynamic equivalence of small and medium-sized hydropower clusters is urgently needed.In addition,due to the increasing scale of modern power grid,small and medium hydropower groups are no longer far away from the main system through a single connection line.So the parameter identification method based on single connection line is not sufficient so far.In this paper,a method based on measurement of small and medium hydropower is proposed.When it comes to the method,the input is the measurement from the connection line between the equivalent area and the main area.Aiming at the different composition of the equivalent region,different equivalent model combinations are adopted to improve the equivalent precision.The four-order Runge-kutta method is used to calculate the dynamic equations.The original hydropower area is replaced by the selected model with the optimal parameters identified.By comparing the power curve between the equivalent region and the research area to determine whether the dynamic response of the system is similar to that before the equivalence.Secondly,there are still somethings to improve in the optimization algorithm:1)low accuracy;2)partial convergence and so on,so the adaptive differential evolution algorithm is selected to optimize the identification parameters in this paper.Each iteration of this method updates the variation scale factor F_i and the crossover probability factor CR_i,so that a small number of parameter groups in the iteration may be away from the partial convergence point.Therefore,in the process of crossover mutation,the randomness of change is added,and the problem of partial convergence is solved effectively.Finally,this paper studies the equivalence method of the three-region interconnection system,and proposes a dynamic equivalent method for small and medium hydropower cluster based on the three-region interconnection system model.The method is also used to determine the value of the equivalent parameter group by the power curve on the connection line between the equivalence region and the study area.For equivalent methods with single connection line in the modern power grid are hard to adapt to the interconnected system of regional equivalent problem,three regional system equivalent method can be used in the dynamic equivalent research in the modern large-scale power system with several equivalent areas.The simulation softwares of this paper are PSASP,BPA and MATLAB.The data of the calculation examples are from the domestic latest network data in Sichuan and the Hunan power grid.Through the simulation of actual grid data,the validity and precision of the proposed method are verified.