A Study On The Expansion Planning Of Distribution Systems Considering Distributed Generations

Distributed generation(DG) plays an increasingly important role in the distribution network by providing different benefits, such as reducing investment and operation costs, decreasing power losses, enhancing system stability and reliability, improving voltage profile, increasing overall energy efficiency, attenuating environmental impacts. However, different types of DG has its own operating characteristics. As more and more DG units have been connected in the distribution network, inappropriate placement of DG units may not only increase system losses, network investment and operation costs, but also affect the power quality and relay protection of the distribution network. There are more challenges to the planning of distribution network with the widely application of DG units. Therefore, for fear of the negative impact of distributed generation, it is important to investigate the method of distribution network expansion planning with DG units. Then the main work of this paper is the expansion planning of distribution network considering distributed generations type and uncertainties.Firstly this paper introduces the research background and significance, including the definition and advantages of DG as well as the content of the traditional planning of distribution network. What’s more, this paper introduces the research status, including the planning methods, models and optimization algorithms.Then four types of DG (wind turbine generator, photovoltaic, gas turbine and energy storage battery) are adopted in this paper. Uncertainties related to demand and power supplied by DG units are represented through multi-state probability models. Thus a multi-stage planning approach and an integrated methodology for expansion planning of the active distribution network were established. The former uses the idea of "first network, then power sourse". The proposed approach includes two planning stages. The first stage constructs the structure of distribution network with a close-loop framework. The second elects the candidate buses for DG units based on the power loss optimization index, voltage stability optimization index and comprehensive index. Thereby optimizing the locations and capacities of DG units. The latter adopts the idea of integrated planning of distribution network and DG units. Double nested algorithm is used to solve the optimization problem, the upper planning a new radial distribution network and tie lines, the lower planning the position and capacity of DG, which use the method of index evaluation to elect candidate buses for DG units. A constriction-factor particle swarm optimization-simulated annealing (CFPSO-SA) algorithm is proposed in order to overcome the local minimization problem of PSO.Finally, a an actual test system is built in MATLAB, results using the two planning methods suggest that the methods proposed in this paper are effective for the problem of distribution network expansion planning adopting DG units.