Microgrid Fault Restoration Method Research

With the rapid development of economy and ceaseless acceleration in industrialized process, the request for microgrid (MG) is increasing rapidly apart from the higher requirements for the power supplied by the conventional interconnected power grid. MG consists of various kinds of small stand-alone power systems and the distribution networks with distributed generation (DG) integration. There is significant difference of structures and power supply modes between microgrid and interconnected power system. Therefore, when fault restoration problems are studied, the emphases in the two types systems are different. This thesis takes shipboard power system (SPS) and the distribution networks with DGs for instance to study the fault restoration problem.The current research methods and achieved results in the field of fault restoration in shipboard power system and distribution network with DGs are summarized at first. Then the insufficiency and the flaw of the existing methods are pointed out. Compared various methods for the fault restoration rearch of SPS, this thesis applied the multi-agent system (MAS) technology into the restoration problem of distribution network with DGs. The structure of the whole thesis is listed as follows:Firstly, the fault restoration optimization model of independent shipboard power system is proposed, and the Binary System Particle Swarm Optimization (BPSO) is used for the optimization problem solution. Undirected graph is used to describe the network topology of the shipboard power system, and the adjacency matrix is used to store the network topology information. The encoding method of this algorithm is based on the power state of all loads, the opening and closing state of important cables, which can reduce the encoding length effectively. Based on depth first search after fault, the network connectivity is analyzed in order to confirm the range of particle code value, which can shorten the searching space and improve the convergence speed of the algorithm.Secondly, the mathematic programming model of independent shipboard power system is proposed and the Branch and Bound Method is used for the optimization problem solution. Mathematical programming method proposed in the early literature has been improved in this thesis. According to the actual situation, considering the reconfiguration of major network can make the network structure more flexible, and increase reliability of the SPS. The simulation results indicate that using mathematical programming to solve the fault restoration problem can obtain stable optimal solution.Thirdly, the basic concepts, architectures, and development history of distributed artificial intelligence, agent, and multi-agent system technology are introduced. The current situation and the developing trend of the application of MAS technology in the electric power system are summarized. The Java Agent development framework (JADE) and its programming process are introduced in detail.Fourthly, a prototype of MAS is proposed to reconfigure the SPS in order to maximize the number of served loads with highest priority. Agents of the MAS have the ability of illation, and makes reasonable decisions according to different environments. The MAS is implemented using Java programming language and JADE. The simulation results of typical SPS fault restoration cases demonstrate the feasibility and the advantages of the proposed MAS.Finally, a fully decentralized MAS has been proposed for load restoration of power distribution network with DGs. The proposed multi-agent system consists of bus agents (BAs). Every BA in the MAS has the ability to lead the restoration work independently. The restoration work could be completed by the communication and cooperation among the BAs. In order to ensure smooth communication, a depth-first communication mechanism (DFCM), similar to the process of depth-first search (DFS), is proposed. The MAS is capable of dealing with a single fault or cascading failures. The proposed multi-agent system is implemented based on JADE. The simulation results of typical fault cases verifiy the feasibility of the proposed MAS.