Investigation On The Thevenin Equivalent Parameters Analysis And Weak Node Identification Method Of Power Systems

The source and load of power system are becoming more and more diversified.The influence of their power generation characteristics and load characteristics on the safe and stable operation of power grids has attracted wide attention.T he combination of Thevenin equivalence and power grid stability can improve the identification efficiency of power grid instability through impedance matching principle.So far,Thevenin equivalent parameter identification methods are based on various assumptions,which have certain limitations.Moreover,some identification methods have not considered the reasonable constraints of the parameters to be identified,resulting in serious deviation of the results obtained.Therefore,it is particularly important to seek a highly accurate and adaptable identification method for Thevenin equivalent parameters.First,we classify the existing parameter identification methods from the mechanism layer to the identification method based on the multi time local measurement,the network simplification method based on the single time full network measurement,the identification method based on the single time local measurement and the virtual disturbance.The parameters,applicable preconditions and existing problems of various methods are summarized and analyzed.By setting appropriate disturbances on the side of the system and the load side,three typical methods of identifying the parameters of the least squares,network analysis and load linearization are simulated and verified.The fundamental reason for the difficulty of identifying Thevenin equivalent parameters in power system is the nonlinear influence of generator nodes and load nodes.In this paper,the equivalent method of electric power system which converge generator node and load node respectively is proposed.Using star triangle transform to decouple the equivalent generator node and equivalent load node,three classification aggregated equivalent networks are obtained by network simplification.The calculation of equivalent parameters only requires any two of the power,voltage,and current at each node.If the measurement error is not considered,the calculation process has no approximation.By connecting the equivalent load branches to the equivalent generator node,the studied load node and the internal system,the impedance of the classified aggregated equivalent network can be properly merged,and the equivalent impedance parameters obtained by the different merging methods can be obtained,and the identification of the weak nodes of the system is based on the impedance module index.The simulation results of the IEEE standard system are compared with the analytical equivalent method and the classical least square method,and the effectiveness of the proposed method is verified.In order to simplify the process of the equivalent parameter,this paper uses the leading generator node instead of the equivalent generator node,which can reduce the data measurement demand,and further simplifies the weak node id entification method.The simulation results show that the impedance mode index obtained by using the dominant generator node information can accurately identify the weak nodes of the system.