Research On Static Voltage Stabilirt Analysis Method Based Power Flow Algorithm

With the growing power demands and the rising interconnection degree of power grid between regional, the power system is closer to the voltage operating limit, Therefore, the problems of voltage stability have become increasingly serious. Especially some large blackouts which were caused by voltage stability, which is not only caused huge economic losses, but also brought greatly inconvenience for people’s life. In recent years, therefore, the problem of voltage stability analysis is more and more attention by experts both at home and abroad. Considering the influence of the load change on the system static voltage stability, this paper make a research of static voltage stability analysis method based on flow algorithm.The following is the main content of this paper.(1) Research on the methods of voltage stability analysis and probability flow algorithm. Starting from the concept of voltage stability, this paper analysis the cause of the voltage collapse and so on. At the same time, this paper also describes the research status of static voltage stability analysis method and probabilistic flow algorithms.(2) Analysis the static voltage stability with the Improved Continuation Power Flow (ICPF). This paper introduces the conventional Newton-Laphson method to solve the equation, which is used as the basic flow method for static voltage stability analysis. And also introduce the Continuous Power Flow algorithm based on this method. Describe the Improved Continuous Power Flow algorithm, which can analyze the system static voltage stability under load increasing at the single node, multi-nodes or random nodes in normal or line fault operation ways.(3) Analysis the static voltage stability with the Improved Bisection Searching Technique(IBST). At first, the basic principle of binomial searching technique and its application in mathematics and computer is descrided, and then combined with the binomial searching technique which could solve the load growth factor under voltage collapse state for power systems, draw the upper branch of the PV curve, get the load and voltage information at voltage collapse point. At last, put forward the Improved Binomial Searching Technique to analysis the static voltage stability in specified load growth ways.(4) Analysis the static voltage stability with the probabilistic load flow algorithm based on the semi-invariant. Considering the uncertainty of generation or load, the probability voltage equations which is built with a linearized AC model at each node could be shown. Combining with the concept of semi-invariant and Gram-Charlier expansion theory, this paper supposed a method to calculation the Probability Density Function (PDF) of the voltage at each node. According the PDF, we can judged whether voltage amplitude is the allowable fluctuation or not directly. And also can analyize the ability of the network structure defend against load growth.(5) Case studies. Applying these three methods to the IEEE-30nodes and IEEE-14nodes system. Composing the grograms at the MATLAB platform. At first, the ICPF and IBST are all applied to the IEEE-30nodes system. Calucate the voltage amplitude and voltage change rate for each node in different load growth ways under normal operation or line faults state. Analysis the static voltage stability by these indeies. And also compare the results calculated by the ICPF and ISBT, the results shows that the ISBT is superior to the ICPF in convergence, accuracy, time cost. And then, apply the probabilistic load flow algorithm based the semi-invariant to paint the PDF image of volage amplitude at each node under normal operation or line faults state. Analysis the static voltage stability with the PDF. At last, compare the results calculated by the probabilistic load flow algorithm based the semi-invariant and the Monte-Carlo method. It shows that the probabilistic load flow algorithm based the semi-invariant is superior to the Monte-Carlo method in accuracy, time cost of operation and the storage space.