Research On Fault Effect Analysis And Protection Configuration Of Micro-grid

At present, the stability and reliability of the power grid has been a great impact ,the large-scale wind power, solar photovoltaic power generation systems and other renewable energy inputs have resulted in great impact on the stability and reliability of the power grid,because the outputs of renewable energy are unstable and random.If the renewable energy directly gets into the grid,a lot of problems will occur.The use of micro-grid technology can solve the various problems.Although the micro-grid has many advantages, while the protection of micro-grid may also face some technical challenges. The traditional distribution network protection strategy applied to the protection of micro-grid is not feasible. The reason is that the micro-grid protection scheme should consider the following factors: the two-way power flow in the feeder, the presence of the distributed power supply, and the magnitude of the fault current in the independent operating mode.In this paper, we mainly study the fault effect and protection configuration method of micro-grid. Firstly, we introduce three kinds of micro-grid architecture, composition unit and operation control mode, and then analyze the detailed theory of inverter power supply under different faults.We focus on the islanding effect of micro-grid in the islanding mode. The technical principle of active frequency offset method(AFD) and the positive feedback active frequency offset method(AFDPF) are introduced, with their advantages and disadvantages being analyzed. Then, an improved island detection method is proposed. By detecting the size of the initial time frequency deviation, the initial chopping factor and the direction of the disturbance are determined, and the absolute value feedback of the cumulative frequency deviation is applied to the common point. As compared with AFD method and AFDPF method, it has the advantages of small blindness and high efficiency.In the end, we propose a comprehensive protection method based on current mutation. In the case of failure of micro-grid, this method uses the obvious difference of current flowing through fault line and non-fault line to judge the exact location of micro-grid fault, starting the protection of the remaining distributed power and load from failure to continue running on the island. Through the simulation analysis of the proposed protection scheme, the feasibility of the protection scheme is verified.