| Distributed generation (DG) has been widely used in the deregulated electric power systems for its immense benefits. Studies of distributed generation and its application in electric power system become more important to utilize DG efficient and refine power system operation. Based on the introduction of various types of distributed generators, a systematic study on planning for grid-connected distributed generation system, the potential of DG providing ancillary service, the backup generation application, negative impacts of DG on power system and its control strategy is carried out in this dissertation. Contributions are summarized as follows,1) Following the trend of developing grid-connected distributed generation system, an optimal generation expansion planning model is presented in this paper. The system optimal results and operation performances under various transmission system scenarios are determined by using heuristic method. Effects of transmission system outage indexes, real time price and randomness of renewable generation resource on the system design are discussed. Optimal results and hourly system operation performance suggest the advantages of grid-connected distributed generation system. They also provide guide for expansion planning of distribution system with DG.2) The potential benefits of DG providing ancillary services are discussed. By introducing "microgrid" concept, a novel AGC dispatch model in distributed system is proposed. By comparing the optimal AGC dispatch results in the two cases with and without DGs, the economic prominence of DG to provide AGC services is discussed. By selecting DGs with good regulation characteristics, simulations to frequency and inadvertent interchange are performed. The results indicate the technical feasibility of DG to provide AGC services too. Based on the contribution of generators to the Area Control Error (ACE), the cost of AGC services is allocated by a transparent proportional method.3) Distribution system reliability becomes important in electric power market. This paper introduces DGs as backup generators in distribution system. The optimal reserve procurement model aims to balance the interruption cost and reserve purchased cost. The effect of Forced Outage Rate (FOR) of distributed generators is included in reserve purchase cost, while the interruption cost is calculated accurately according to the Sector Customer Damage Function (SCDF) of different types of load. Case studies show that the model increases the economic benefits and decreases the crossover subsidy of reserve caused by some traditional reserve procurement method. The optimal results suggest DG can improve load and system reliability effectively, especially for those loads near DGs.4) With the numbers of wind power generators increasing rapidly, they may cause voltage variations due to the random-like outputs of wind turbines. To solve this problem, we introduce Static Var Compensator (SVC) into distribution systems, and combine the reactive power support from distributed diesel units for voltage control. An optimal reactive power planning model is proposed in this paper. Monte-Carlo simulation is used to simulate the uncertainty of wind power generation. The locations and the outputs of SVCs and distributed diesel units are determined by hybrid encoding genetic algorithm. Case studies show WPG has characteristics of generating active power randomly and absorbing reactive power at the same time. By installing enough capacities of SVC, the system loss and voltage deviation can be reduced significantly.5) Since the main purpose of installing SVCs is to regulate the voltage variations caused by wind turbines, a shapley value criterion based on cooperative theory is proposed to allocate the reactive power support cost. The allocation result is equit and acceptable to all participants. It provides some economic signals to decision-makers to determine the appropriate locations of DGs and provides a new way to allocate some grid-connected cost caused by DG.
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