Research Of Microgrid Fault Characteristic And Protection Principle Based On DIgSILENT

With the growing demand for electricity, energy consumption continues rising and the earth environment worsening with time, the traditional mode of electric power production faces severe challenges. Under this background, the development and utilization of renewable energies, including wind energy, solar energy, as well as biomass energy, are gaining extensive attention, the distributed generation technology represented by renewable energy has obtained fast development. The proposed micro-grid provides convenient conditions for distributed utilization of renewable energy. The micro-grid comprises of distributed power supply, load, energy storage, and monitoring equipment, etc, has the ability to run independently and could be operated parallelly with the power grid.Micro-grid connected distributed generation changes the structure and power flow of distribution network, which transforms the distribution system from single supply radial network to multi-source network. The changes in the distribution network have impacts on the existing protection and operation mode. Therefore, it is necessary to put forward a new protection strategy for protection issues of distribution network with distributed generations connected.Firstly, on the basis of mathematical model of inverter interfaced distributed generation and micro-grid, the simulation model of inverter interfaced distributed generation and micro-grid are built on the DIgSILENT/PowerFactory software platform in this thesis. The fault characteristics of inverter interfaced distributed generation in two common control modes:PQ control and V/f control are analyzed; The fault characteristics in different fault conditions in micro-grid lines are analyzed, when micro-grid operating in island or grid-connected mode. And the influence of the conection of the distributed generation and micro-grid on the original distribution network protection relay protective device is analyzed.The two main problems of micro-grid are about the tie line protection and internal protection. For the protection of tie line, according to the importance of the load, the power exchange between the micro-grid and distribution network and the relevant micro-grid interconnection standards, the influence of micro-grid island and fault through operation are discussed. Then the common isolation strategy of micro-grid and utility are summarized. On this basis, corresponding tie line protection principles and programs for different isolation strategies are proposed. For the protection of internal micro-grid, this paper mainly discusses the two kinds of typical protection strategy:low voltage protection and current differential protection. On this basis, a protection program based on current phase comparative principle was suggested, which combined with voltage offset protection to form a holistic protection program of the micro-feeder protection and micro-source protection. The suggested protection program could be applicable under both island and grid-connected operational models. Finally, the new protection scheme is compared with current differential protection, and the simulation results show the superiority of the new protection performance.