Analysis And Control Of Voltage Sag In Distribution System With Microgrids

China has the vast territory and abundant resources, but the distribution of resources is extremely unbalanced. It is an efficient and environment-friendly way to build power plant nearby pit and transport the energy from plant to load center through the ultra high voltage (UHV) transmission line. But the wind, solar and biomass energy can be transported through long-distance and large-scale way in limited places. So most renewable energy is developed and utilized in a distributed way. Different types of complementary energy form a common micro-network and the primary energy can be converted through variety of devices to second energy, which effectively improves the efficiency of the utilization of primary energy. At the same time the energy storage is added into micro-grid, which can be used to smooth the power fluctuations and ensure the voltage and frequency stability and balance of generation and load. Micro-grid brings convenience to our life, but it contains a large number of power electronic conversion devices, which need higher power quality and requirements. Voltage sag may lead to abnormal operation of power electronic devices, which may cause the collapse of micro-gird and users may suffer huge economic losses. So the study of voltage sag of distribution system containing micro-grid has important significance and it can improve the power quality of micro-grid and distribution system.In this paper, the structure, key technology and main micro sources of the micro-grid are studied. The simulation model of distribution system with micro-grid is established on the platform of PSCAD software and the mechanism of voltage sag in the distribution with micro-grid is analyzed. According to the characteristics of micro-grid and micro-sources, a voltage dynamic compensator suitable for distribution system with micro-grids has been put forward, which coordinately controls the PV unit and cell to provide energy for DVR. Finally the compensation effect of DVR is verified through the simulation. The results show that the DVR can be applied in distribution system with micro-grids during normal running and it can effectively improve the power quality of distribution system with micro-grids.