Research On Fault Diagnositc Technology For Power System Based On Information Fusion Theory

The security is very important for power grid running. When the fault is occurred, the fault occurred site and reason need to be detected exactly and rapidly to lessen the influence that caused by the fault. But because of the complexity of the power system, it is not practical for the operators to judge the fault immediately only by experience. At the same time, the detected information will be incompletion and uncertainty inevitably. That will enhance the difficulty of the fault diagnosis. Therefore, it is very important to research the fault diagnostic approach that can solve the problem when the detected information is incompletion and uncertainty.This dissertation researched the fault diagnostic problem of power system with incompleteness information based on the analysis of fault diagnostic mechanism,model design of the system and information fusion after the investigation of literatures. The main research content include: fault diagnostic model design, acquired method of incompleteness information, design and application of fusion model about D-S evidence decision rule and entropy based Markov chains, fault diagnostic methods with incompleteness information.Main contributions of this dissertation are stated as below:(1) Put forward a layered model constructed method for the construction of power system fault diagnostic model. In order to solve the problem of fault illation in power system, Petri nets theory is applied in the research. The Petri nets model of the element in grid is designed by backward illation method. The connection of element models will compose in area diagnostic model. The hierarchical structure of the model can solve the problem that the model state will expend quickly when the system is complexity. At the same time, the acquired model of absent data is designed based on the Petri nets if the detected data is incompleteness. The outputs of the information acquired model are the input of the fault diagnostic model, and form a layered model format in logic. In addition, the nested design method of the model is put forward in the process of the model design. The method can resolve the problem of complexity fault diagnosis.(2) The concept of probability Petri nets and the illation mechanism with incompletion information is defined to solve the problem that the detected information of fault is uncertainty. Combine the Petri nets with probability will find the concept of probability Petri nets. Probability Petri nets can achieve the logic illation with information uncertainty. Depending on the comparability of Petri nets and Bayesian network, a transplant method is put forward in the dissertation. The method can transplant the Petri nets into Bayesian network to calculate the generant probability of the absent data by Bayesian illation technique. Then the obtained probability of the absent data can be used into the diagnostic model.(3) The information fusion technology is used to enhance the precision of diagnosis by the combination of D-S evidence decision rule and entropy based Markov chains. When the estimate of the absent data has several estimations, the information fusion technology will be used to obtain the consistent output to reduce the uncertainty of the judgement. Because the difference that exist in these estimations is inevitably. Different information fusion approaches need to be choiced according to the state of the estimations to enhance the rationality of the information fusion. Therefore, D-S evidence decision rule and entropy based Markov chains information fusion technologies are researched in this dissertation. According to the characteristic of D-S evidence decision rule, the restricted condition is defined as: F(p_a, p_b)≥max{p_a, p_b}. The choiced criterion of D-S evidence decision rule is defined according to the restricted condition. The selected of the information fusion technology can be achieved by the choiced criterion.(4) The strategy of fault diagnosis with uncertainty information is put forward. The diagnostic process is definitized by the analyzed within information judge model, fault diagnostic model and information fusion model. And the research is described and analyzed in this dissertation by the application of some cases.Finally, the research is summarized in the dissertation, and the research of next step is also proposed.