Studies On Power Flow And Network Reconfiguration For Distribution Systems

Three-phase distribution network power flow and network reconfiguration and dynamic reconfiguration problem are studied in this dissertation. This thesis consists of six chapters. The research significance and the present development of the distribution system power flow algorithm and network reconfiguration method are summarized in the first chapter. In the second chapter, three-phase models for distribution system elements are established, which is the basis of three-phase power flow. In third chapter, three-phase power flow for distribution systems is studied. Based on the three-phase models established in second chapter, the radial distribution network power flow is expanded in order to be capable to deal with different load models and distribution transformer model. At the same time, a three-phase power flow approach for weakly meshed distribution systems based on superposition principle is presented in this chapter. In the fourth chapter, network reconfiguration problem is studied and a reconfiguration approach based on minimum spanning tree and switch exchange method is presented. In the fifth chapter, the dynamic reconfiguration problem is studied and a dynamic reconfiguration method using dynamic programming is proposed. The sixth chapter makes a summary of the whole dissertation.The mathematics models of electric power system elements are the basis of analysis, so the phase domain models of distribution systems elements are first established by referring to some related papers.Distribution power flow is applied in many applications of operation and planning, some optimization problems such as network reconfiguration and service restoration and capacitor placement etc. require hundreds even thousands times of power flow calculation, so the development of rapid and robust power flow algorithm is very important. Based on the detailed three-phase models of distribution elements, the backward/forward power flow method for radial distribution network is expanded in order to deal with different load model types (constant power, constant current or constant impedance) and different load connectiontypes (Wye and Delta) and transformer model. For weakly meshed distribution network, a new three-phase power flow method based on the superposition principle is proposed. The weakly meshed network is firstly divided into two networks using the superposition principle: one is the pure radial network and another is the pure meshed network. Three-phase power flow is solved separately on the two networks. The solutions of the two networks are superposed together, and the final power flow solution is obtained by repeating to solve the power flow of the two networks. The presented method is tested by IEEE 33 nodes system and the power flow solution is given. Moreover, the performance test results of 33 nodes system, 67 nodes system, 123 nodes system, 145 nodes system, 292 nodes system and 961 nodes system are offered. The results indicate that the proposed method has good convergence performance and save memory and has high efficiency.A new real-time reconfiguration approach for large-scale distribution network is presented in this paper. The proposed approach is based on minimum spanning tree algorithm and switch exchange method. The approach uses minimum spanning tree algorithm first to reconfigure the distribution network preliminarily, and the reconfiguration result is close to the optimal solution, and then the switch exchange method is used to reconfigure the distribution network accurately to obtain the optimal or near-optimal solution. In the preliminary minimum spanning tree reconfiguration, the simplified power flow method and approximate loss calculation method are adopted, and the power flow calculation is only performed on the affected circuits, so the time consumption is very short. In the switch exchange reconfiguration, the accurate power flow calculation is used to guarantee to obtain the optimal or near-optimal solution. Moreover, the method for forming distribution network graph is also introduced. The test results of a real distribution system indicate that the proposed approach has high efficiency and good reconfiguration result. It can be applied to real-time reconfiguration for large-scale distribution system.A new dynamic reconfiguration approach based on dynamic programming is presented in this paper. The dynamic reconfiguration problem is solved from two respects; One is to determine the optimal time interval of every reconfiguration when the reconfiguration times of a day are given; another is to determine the optimal reconfiguration times of a day. The dynamic programming equations for given reconfiguration times of a day...