Study On Distribution Network Optimal Operation With Grid-Connected Distributed Generation

In recent years, along with increasing global concerns for environmental protection and energy saving issues, and with wind power, photovoltaic power generation and other renewable energy technologies becoming more sophisticated, the Distributed Generation (DG) technology has become a hot research topic. Therefore, after DG connected into the distribution network, the distribution network structure, operation and control mode will be tremendous changed, and the distribution automation and demand side management need to consider the coordination between DG and distribution network control, distribution system control and management will become more complex. At present, domestic and foreign researchers have done much research in the DG impact on the power system, but few of them studied on the distribution system optimal operation with grid-connected DG. Thus, study of the distribution system optimal operation after DG connected in the distribution network become an urgent need when large-scale DG access to distribution network, it have important theoretical and practical significance.In this dissertation, the distribution network optimal operation with grid-connected DG is studied. The contributions of this dissertation are summarized as follows:(1) To calculate the power flow of distribution network connected with various DG, a three phase power flow algorithm based on forward and backward substitutions that can cope with DG modeled as PV or PQ nodes is proposed. First, the models of the wind turbines, photovoltaic system in power flow calculation are presented. During the coping with DG modeled as a PV node, the positive sequence voltage magnitude of PV node is used as voltage regulating parameter, which represents the automatic voltage regulation mechanism of a generating unit properly. The sensitivity compensation method is used to calculate the amount of reactive power compensation of PV node. Finally, the correctness of the proposed algorithm is verified by the calculation results of IEEE34-bus test system, and the impacts of various type of DG on distribution network voltage are researched.(2) In this dissertation, based on the PSO, a joint optimization algorithm of network reconfiguration and injected power of DG is proposed. In this algorithm, the reconfiguration result influenced by the DG injected power is considered and the DG is treated as a dispatchable device. Through combining the network reconfiguration and the DG power injection optimization simultaneously, the power quality and power supply reliability of the distribution network are improved. When serious failures result in large area power blackout, a distribution system service restoration method using DG islanding technique is proposed. In this algorithm, DG switch to the islanding operation mode using islanding algorithm to maintain the power supply for the important load first, then a service restoration method based on the binary particle swarm optimization is proposed to restore non-failure power blackout area outside the islanding. Finally, the correctness of the proposed algorithm is verified.(3) In this dissertation, the reactive power optimization algorithm in distribution network considering doubly fed induction generator (DFIG) wind farm is proposed. First, the mathematical model of the DFIG wind turbine is developed, and the reactive power generation and absorption capacity for each generated active power of the DFIG wind turbine is analyzed. Utilizing the reactive power regulation capability of DFIG, wind farm made up with doubly fed induction generators is proposed to use as the continuous reactive power source to take part in the reactive power optimization in distribution network. In the proposed algorithm, the reactive power output of the wind farm is utilized as the constraint, and the relationship between the wind farm reactive power regulation capacity and the connection point voltage and the wind speed is considered, finally, the real power loss minimization is chose as the objective function and the particle swarm optimization algorithm is applied to solve the problem.(4) Considering both the distribution network reactive power optimization and reconfiguration are two main measures to optimize distribution networks, a joint optimization algorithm based on an improved hybrid particle swarm optimization with wavelet mutation algorithm (HPSOWM) combining reactive power control of wind farm and network reconfiguration is proposed. In the proposed joint optimization algorithm, reactive power output of wind farm and status of switches are utilized as the control variable to find the optimal network structure and the optimal reactive power output of wind farm for losses minimization and voltage profile improvement. The simulation results show that the joint optimization algorithm gets better solution results than using the wind farm reactive power control optimization or the network reconfiguration alone.