| In recent years,the scale of power system is expanding day by day,which plays an increasingly important role in all walks of life and brings significant benefits to social economy.However,due to the complexity of the power system and the limitations of the construction of power generation and transmission services,it is a challenge for the grid to maintain voltage stability.Many voltage collapse accidents around the world have caused huge economic loss and social impact,which has sounded the alarm for people.It is urgent to further study the internal mechanism of voltage stability,obtain effective analysis and monitoring tools to accurately evaluate voltage stability conditions and determine load stability margin to prevent voltage instability.In the face of complex power grid topology,it is difficult to consider the voltage stability of all nodes,and often need to pay attention to those important load nodes.The complex power grid can be simplified into a simple system composed of equivalent impedance and equivalent potential through Thevenin equivalence,so that researchers can quickly analyze and evaluate the voltage stability of the concerned load nodes.Among them,the "impedance matching" method based on Thevenin equivalent has been widely concerned,but the relevant research shows that this method may produce incorrect results for multi load system.In order to solve this problem,a new method of voltage stability analysis and on-line monitoring is proposed.In this paper,based on the principle of Thevenin equivalence,some problems of this kind of method are analyzed,and its correctness in multi load system is verified by a simple 3-node system.Then,this paper applies the fixed point principle to the voltage stability analysis,and proposes an analysis method to study the voltage stability by calculating the matrix norm.The core idea is: for a certain time section,the network equation can be expressed as a self mapping nonlinear system related to the voltage vector of load nodes;if the system has only one in the voltage measurement space The system is voltage stable at a given time section.An example system of 5 machines and 18 nodes is used to test and compare the proposed method.The test results verify the effectiveness of the proposed method.On the basis of the above,in order to further identify the critical load accurately,this paper proposes an identification method based on eigenvalue isolation,which mainly identifies the eigenvalue through the Gayle circle theorem,so that it can achieve one-to-one correspondence with the physical nodes.The correctness of this method is proved by the calculation and analysis of IEEE30 and IEEE57 systems.Finally,based on the classical "impedance mode criterion",a new criterion of static voltage stability,voltage drop ratio criterion,is proposed,and its validity is analyzed and proved.The results of IEEE30,IEEE57 and DC systems show that the voltage drop ratio criterion has the advantages of less calculation and accurate judgment,which can be used not only for off-line analysis and evaluation of static voltage stability,but also for on-line monitoring of voltage stability. |
