Research On Planning And Optimal Operation Of Distribution Network Including Decentralised Generation

The new distribution system, which contains distributed generation and demand-side resources, can make up for the shortfalls of the centralized power generation and transmission, ensure the secure operation of the grid and maximize the use of a variety of energy resources. The single-function distribution system will convert into a multi-function power exchange system, which includes electrical energy production, storage, transmission and distribution. This situation brings new challenges to the planning, operation and control of the distribution system.The main work and achievements of this thesis include:studying the planning of a distribution network that contains distributed generation and proactive load and establishes a bi-level programming model; studying the reconfiguration and optimal operation of the distribution network and establishes an integrated optimal operation model; A decimal genetic encoding method, a network connectivity identification method, and radiativity determination method is proposed; researching on the interaction mechanism between the distribution network reconfiguration, the transformer economic operation, and the distributed generation, a comprehensive optimization model of multi-time scale is established. The specific work is as follows:1. Aiming at the problem of distribution system planning with multiple resources, a bi-level programming model is proposed. At the first level, the distributed generation, the proactive load, and the main grid power supply is treated as the equivalent generation. The cost-time characteristic curves of each kind of power supply are established subject to the fixed cost and variable cost per MW, According to the principle of minimum cost, based on the characteristic curve and the annual load duration curve, the operating duration and the corresponding load level in the load curve of each kind of power supply in the planning year is calculated, and then the configuration capacity of each type power supply is obtained. At the second level, the minimum total cost is treated as the objective function to determine the distribution network grid planning, installation location and distribution capacity of the distributed power. Configuration capacity of all kinds of power supply at the first level is treated as constraints. Finally, the ordinal optimization theory is applied to solve this model. The planning method in the thesis can select distributed power types and determine the working hours of the distributed generation, which improves the economy of the planning process and the accuracy of the economic indicators. Simulation of A6-bus system and the IEEE-54system shows the effectiveness of the proposed method.2. Three solutions are proposed for the problem that a large number of infeasible solutions in the distribution network reconfiguration. The solutions are:(1) decimal encoding method. If the interconnection switch is closed and the network forms a loop, a sectional switch in this loop must be opened to keep the radiativity of the distribution network. Therefore, the interconnection switch determines a looped network. All of the switches are individually numbered in every looped network which determined by the interconnection switch (from1to the total number of the switches in a loop). In each loop only one switch is allowed to open, and all opened switches in the ring constituted a network topology. Coding the gene locus with the loop which is determined by the interconnection switch, the value of the gene locus is the number of the switch that is opened.(2) Radiation network identification method. In the decimal encoding method, if the gene loci in chromosome is with the same value, it means that a common switch in the multi-loop network is open and forms a loop network. The topology is infeasible solutions and must be ignored;(3) Network connectivity judgment method. Creating a connectivity matrix, an isolated point can be found by means of a judgment of the connectivity matrix diagonal element. The above three methods are not only suitable for the genetic algorithm, but also appropriate for the methods of distribution network reconfiguration. The method can be used to filter the possible topology of the distribution network and establish a feasible topology database and hence can improve computational efficiency and save calculation time.3. In allusion to the problems of distributed generation and coordinated optimal operation of the distribution network, the relationship between the distribution network reconfiguration, power loss and economic power allocation of the distributed generation is analysed. The distribution network reconfiguration and distributed generation optimal operation model are established. Because the distribution network reconfiguration can decrease the power loss, i.e. it can reduce the cost of purchasing electricity from the major network, minimize the total cost. Therefore, the major network electricity expenses, distributed generation expenses and proactive load expenses are included in the objective function. The family eugenics is applied to solve the reconfiguration problems and the interior point method is used to calculate the optimal power flow to obtain the optimal generation schedule. The model and method improves the theory of optimal operation of the distribution network. The test of the IEEE3-FL system and the IEEE-33system shows the effectiveness of the proposed method.4. The economic operation of transformers is an important energy saving measure. Thus, its coordinated optimization with the distribution network reconfiguration and distributed generation can improve the efficiency of energy utilization in a wider range. This thesis introduces the theory and practice of the economic operation of transformers and the effect of switching frequency on the economic operation of the transformer. The mutual influence and interaction mechanism between distribution network reconfiguration, transformer and distributed generation are also analysed. A multiple-time-scale integrated optimization model, which consists of distribution network reconfiguration, transformer and distributed generation are proposed. The model can consider the number of switching operations and operation costs and be solved by a distributed estimation algorithm. The test of the IEEE3-FL system shows the effectiveness of the proposed method.