Modular-based Fault Tree Analysis Method And Its Application On Power Grid

As an effective tool,the fault tree analysis(FTA)is significant for system reliability analysis.However,the advancements in functions of modern complex systems have increased the complextity and diversity of system structure,which makes the traditional FTA methods inefficient when dealing with reliability analysis of large-scale complex systems.For traditional FTA methods,as the size of fault tree grows,the computational complexity exponentially increases.Current relevant works have limitations on module searching and BDD-based converting technique of fault tree.This thesis focuses on the study of an innovative modularization algorithm for fault tree preprocessing and implementing the conversion from fault tree to BDD.To reduce the computation time and storage of FTA method,the fault tree is firstly preprocessed by modularized method,and then solved using binary decision diagram(BDD).Main contents and contributions in this thesis are summarized as follows:(1)Fault tree modular decomposition can obtain several independent modules and can effectively reduce the computational cost.In order to solve the problems of the current linear algorithm operation complexity and the resource consumption of parallel algorithms,a new and efficient fault tree modularization algorithm is proposed in this thesis.The algorithm uses the characteristics of prime numbers,refers to the network flow knowledge in graph theory and combines the features of the fault tree's own structure,and innovatively uses the bottom-up approach to calculate the tree.Compared with the linear and parallel algorithms,the proposed algorithm has simple traversal complexity and only needs to traverse the fault tree once to achieve the same global module searching.The verification results indicate that the proposed modular algorithm is superior in terms of simplicity and resource consumption and significantly reduces the time required to find the module.(2)In order to further expand the practicality of the FTA method,the BDD technology is introduced to implement FTA.During the research of BDD method,the research focuses on BDD-based fault tree automatic transformation methods.With the help of ite(if-then-else)operators,a recursive algorithm is designed to transform the fault tree into BDD.Measwhile,the differences in the BDD structure obtained from different indicators are compared in the fault tree to BDD conversion results.The results demonstrate that the results obtained by this criterion are better.(3)In the engineering application,the modular technology and BDD method are combined and applied to the fault tree analysis of the power grid transformer.The fault tree of the power transformer is constructed by learning a large amount of literature,and the reliability analysis of the power transformer is realized by using the proposed fault tree modularization algorithm and BDD technology.The demonstration and verification results show the feasibility and practicality of the fault tree analysis method proposed in this thesis.The main contributions of this thesis are to propose a new modular algorithm to achieve the early optimization of the fault tree,and to achieve the transformation of the fault tree to the BDD.The proposed methods are all verified with the engineering application.The results obtained in this thesis provide important theoretical basis and practical reference for further FTA method research and more engineering applications.