| For the resources are increasingly depleted,the environmental degradation seriously,the inherent shortcomings of the large power system,and the electricity market reform in worldwide,distributed generation has been making a rapid development nowadays.With the number of the distributed generations which in the proportion of distribution network are growing,it has also produced some adverse effects,such as voltage regulation making complication at line,the lectotype and configuration of relay protection has been difficult,short circuit capacity will be increase,and easily to damage the equipment in fault,has a greater disturbances for power quality.In order to reduce the adverse impact of distributed generation,and also played an active role by distributed generation,micro-grid has been proposed,that is make the distributed generation and the load as a subsystem for the distribution network. Micro-grid has been concerned more than ever.However,a microgrid can operate in both the grid-connected mode and the islanded mode,and the tidal current in micro-grid has two-way,in this case,the short circuit current will be different in two modes of micro-grid.The traditional protection can't operation properly for the two modes.The protection for micro-grid protection are all just started in domestic and international, but it did not has an effective protection strategy.This thesis is analyzing the impact for protection when micro-grid in the grid-connected mode and the islanded mode, and then proposed the micro-grid protection scheme which based on the fault direction information,by in accordance with the characteristics of micro-grid,this thesis established the micro-source model and the micro-grid model,by using this model, the scheme was simulated.The main work done by the following:①Make a comprehensive analysis about the failure characteristics of micro-source and micro-grid. By describes the aspects of the impact for micro-source when it connected in distribution network, above the possible impact to the feeder in fault location with different on-position by the micro-source. the impact for the reclosure brake, And the impact for micro-source of different capacity. And also analyzed the fault characteristics of micro-grid by three-phase short-circuit fault and two-phase short-circuit fault when it operated in the grid-connected mode and the islanded mode.②The paper advances the protection scheme for micro-grid that uses directional fault information. According to the basic requirements of micro-grid protection, comparing the differences between micro-grid protection and conventional relay protection of distribution network,learning from the principle of double directional blocking differential protection, this paper proposes a protection scheme for micro-grid, which uses with fault direction information, studying on the configuration of micro-grid relay protection; illustrating the action mode of relay under the configuration from the aspects of external fault, internal fault and bus fault of micro-grid.③Be established a simulation model for micro-grid fault. The inverter is an important component to micro-grid, it has a great impact to the fault characteristics of the micro-grid. Firstly the control principle of the inverter is in-depth analyzed. And then used the PSCAD simulation software to build a simulation model of the micro-source and also a simulation model for micro-grid fault.④Be simulated the system protection scheme which proposed for micro-grid.By used the simulation model for micro-grid fault to emulate the fault in micro-grid, above external fault, internal fault and bus fault.and the internal fault divided into two cases: grid-connected mode fault and the islanded mode fault.By the simulation results,it validated the feasibility of the protection scheme for Micro-grid.⑤Be discussed the communication system of protection for Micro-grid,and proposed a structure of the communication system.By analyzed and compared several communication modes which used in distribution network, it determined the means of communication by optical communication.And using the composite optical modem to constructed the communication system for micro-grid protection which based on the basic idea of optical multiplexing technology,and proposed the communication structure of this communication system. |
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