Study On Voltage Stability And Its Application Of Power System Based On Node Coupling Relationships

In recent years,there are many voltage collapse accidents in the world,which have brought great losses and effects to the economic society.The problem of voltage stability has become a key issue in the field of power system.China's power system has a large scale,and modern interconnected power grid has entered a stage of development which covers large power grid,large units,long-distance and ultra-high voltage power transmission.The complexity of interconnected power grid,and the growing demand for electricity,significantly increased the difficulty of maintaining the voltage stability of power system.Under the background of large power grid,the number of nodes is tens of thousands,and it has practical significance to study the coupling relationships between nodes to explore the method of improving the voltage stability of power system.In this paper,a kind of nodes coupling impedance matrix based theory of local voltage stability,was proposed to approximately describe the coupling relationships between nodes.Integrating the analysis method of nodes coupling impedance matrix and the dynamic analysis method,a dynamic impedance matrix was proposed to accurately describe the coupling relationships between nodes based on the analysis of the power flow equations.Based on the study of dynamic impedance matrix,a new method of calculating electrical distance was proposed which can be used for load nodes partition in power systems.The concept of node current and voltage coupling degree was defined,which can measure the influence degree of the load node's current on other load nodes,and the influence degree of the other load nodes on the load's voltage.The comprehensive current and voltage coupling degree measures the critical degree and robustness of load nodes in the region.Taking IEEE 14 node system as an example,the accuracy of using the dynamic impedance matrix and electrical distance which is calculated under the single PQ node load power disturbance to describe the coupling relationships between load nodes was verified,and the correctness of using the node comprehensive coupling degree to measure the critical degree and robustness of load nodes in the region also has been verified.Taking the voltage stability improvement of power system as a configuration target in the progress of reactive power compensation that the study on dynamic impedance matrix is applied to,a configuration method of reactive power compensation is proposed based on load node partition,node voltage stability and regional robustness.Firstly,the load nodes are partitioned through the hierarchical clustering algorithm and the electrical distance which is calculated on the basis of dynamic impedance matrix,when the load nodes were partitioned,a function was projected to select the reactive power compensation node based on the impedance modulus margin which can measure the weakness of the nodes voltage,and the comprehensive coupling degree which can measure the robustness of the nodes in the region.Then the node with the smallest function value in each partition will be selected as the reactive power compensation node of each partition.Finally,the function relationship between the impedance modulus margin and the reactive power compensation capacity was developed based on the least squares method,and a method of estimating the reactive power compensation capacity was given.The feasibility of the reactive power compensation configuration method proposed in the paper has been verified through IEEE 30-node system simulation.