Optimization Strategies For Network Reconfiguration Of Power Systems After Blackout

With the continuous socio-economic development, reliable power supply is becoming more and more demanding. By strengthening the structure of a power system and optimizing its management, the risks of power system failures can be reduced. However, the growing complexity of power systems and the inevitable uncertainties in power system operation increase the risks of power system failures. The July30,2012blackout in India and the August14,2003blackout in the United States and Canada remind that it is important to enhance the secure and stable operation of large-scale actual power systems. These events show that it is infeasible to completely prevent large-area blackouts from occurrence from the technical aspect. Thus, it is still of significant importance to study the power system restoration after a blackout. The power system restoration process after blackout can be divided into three phases:blackstart, network reconfiguration and load pick-up. The main issues of the network reconfiguration are to restore generating units and to establish a stable network, and then to prepare for the comprehensive load pick-up.Given this background, this thesis comprehensively considered the factors associated with the network reconfiguration, and the optimization strategies for network reconfiguration considering mulit-factors are developed. Some significant research results are obtained as follows:1) The uncertainties associated with transmission lines are considered in a multi-objective optimization framework developed for the network reconfiguration problem. Risks caused by the uncertainties associated with the transmission lines are taken into account in the developed framework. Three objectives are included in the developed network reconfiguration model, namely maximizing the total number of the restored generation nodes, minimizing the total capacitance of the path and minimizing the risks associated.2) The topological characteristics of a power system are first addressed, and a new method presented for evaluating the importance of a node based on the concept of regret. A method for selecting the best restoration path is next developed by finding the path with the maximized average importance. Then, a two-stage strategy is employed to optimize the network reconfiguration process.3) A modified method for evaluating the importance of each node is presented based on the electrical relationship among the nodes and the load on each node and a multi-objective bi-level optimization model for the network reconfiguration is proposed. A continuous dynamic Pareto multi-step apoptosis optimization strategy (MSAOP) is next proposed to solve the multi-objective optimization problem of the network reconfiguration problem with multi-step restoration by simulating the physiological characteristics of the cell. This optimization strategy focuses on the stage-wise optimal solution in the restoration path of the generating units, while the global optimality is also taken into account. In addition, the set of network reconfiguration strategies obtained in the restoration procedure can be depicted in the form of a branch graph.4) The network characteristics of a power system and the impacts caused by the failure of reconnecting a transmission line are first addressed, and three indexes for evaluating the importance of each line presented, including the bridging power of the line, the line connectivity, and the power-bearing degree of the line. A new method is next presented to comprehensively evaluate the importance of each line. Then, the interpretative structural modeling (ISM) is employed to direct the network reconfiguration after a complete blackout. With the quick and secure restoration of each generating unit as the premise, the restoration benefit is defined and its maximization employed as the objective to select the generating unit to be restored, with the restored generation capacity and the importance of each relevant line comprehensively considered.5) A hybrid power source with conventional black-start generating units and wind farms included is assumed to act as the black-start power source. A new method is next proposed to evaluate the importance of a line based on the concept of line constriction, and then an index for evaluating the importance of a skeleton-network developed. A multi-objective optimization model is next developed for determining the skeleton-network with the minimization of the restoration risk and maximization of the importance of the skeleton-network to be found as the two objectives.Finally, several conclusions are obtained based on the research outcomes, and directions for future research indicated.