| Because distribution systems interconnect between electric customers and bulk power generation systems and transmission systems, it is critical for both security and stability of power system operation and the quality of power supply. However, development of distribution systems was not highly valued in the past, and its investment amount and management quality were much poorer than those of generation systems and transmission systems. These caused a number of weakness links in the distribution system which has seriously affected the quality of power supply. Based on the forecasting of American Electrical Power Research Institute, there will be more than 60% consumers whose requirement of power supply reliability is higher than 99.9999% and the consumers with reliability requirement of 99.9999999% will also reach 10%. Therefore it is concluded that high quality of power supply would be prerequisite objective of power system development. In recent years, distribution network planning methods had been widely applied in China and the related theories are mature. But in order to satisfy power supply requirement of all kinds of consumers, not only the tranditional distribution system planning should be developped whose purpose is to optimize network structure, but also some special planning such as reactive power optimization planning and reliability-oriented planning should also be worked. Therefore, based on the demand of our electrical power industry, the disseration mainly focuses on reactive power optimization, reactive power devices planning distribution, transformer optimization of On-Load Tap Changing (OLTC) and reliability-oriented planning. Particle swarm optimization, genetic algorithm, fuzzy C-means clustering and sensitivity matrix, are applied and their effectivity and practicality are validated using case studies.(1) At present, penalty function is commonly applied to inequation constraints in reactive power optimization, which is known as soft-constraint method. But the method cannot absolutely satisfy the requirements of voltage and power factor. Therefore, in the dissertation, a"nine palaces"strategy is developed and it is able to adjust the voltage and power factor that exceed limits, In addition, the discretization and chaos strategies are applied to particle swarm optimization. The improved particle swarm method will adapt discreteness of the voltage and reactive power adjustment and avoid running into local optimization. Case studies of the standard IEEE sample system and a real system had been performed. Results show that the proposed algorithm improves the searching speed and the quality of optimal solution in comparison with existing algorighms.(2) The configurations of the existing devices for reactive power compensation in urben distribution networks are not reasonably and effiectively deployed. Therefore, a complete solution is proposed for reactive power planning in distribution systems. Due to the large scale of distrubtion networks, it is not feasible to plan reactive power for each of the substation and the feeder. At first, the large scale of network is divided into many sub areas based on the factors, such as load characteristic using fuzzy C-means clustering. Then, based on the optimal feeder locations for reactive power compensation using sensitivity matrix, the mathematical model of reactive power planning is built by associating the models of minimum power loss and minimum integrative cost. At the end, the configuration of different kinds of compensation devices are optimized using the improved particle swarm optimization algorithm, and the results are popularized to the whole network. Case study shows that the solution of optimized reactive power compensation meets the operation requirement of distribution systes and effectively limits the investment.(3) According to the planning method of reactive power devices in distribution system and the application of an existing distribution system, in the dissertation, a method for optimization of transformer OLTC is presented. The method firstly applies sensitivity theory to detect the locations with reactive power weakness, and considers the substation positions to identify a group of substations whose tap position will be optimized. And then, improved particle swarm optimization algorithm is utilized to compare on-load and under-load tap changing for the major transformers in the selected 220 kV and 110 (35) kV substations in terms of the technical and economic aspects. Finally, conclusion of optimization of transformer OLTC will be made.(4) A planning method is established based on the requirement of reliability-oriented planning. Due to its diversity and difficulty of analysis, the influencing factor system for power supply reliability is defined as the criterion for identifying the weakness of existing network. In order to guarantee the feasibility and reasonableness of planning solution, a method for optimizing the combination of available projects is presented. It considers the complexity among different projects, respects to the limits of project investment and reaches the reliability index. Case study shows that the method is capable to provide reasonable planning solution for the weak infrastructure of existing distribution networks in China and improves distribution system reliability based on limited investment.
|
PDF Full Text Request