| Nowadays, conventional energy resources have been lacking and the environment problems have becoming more and more seriously. So many power experts around the world pay attention to distributed resources. As a highly efficient and reliable way with which distributed generation link to the distribution system, microgrid is becoming a hot research. Microgrid has two kinds of flexible operation mode, it can operates not only as a small independent power system, but also connecting with the distribution system. Microgrid can potentially improve distribution system reliability. Because microgrid is near the load generally, microgrid does not require the construction of transmission line. To a certain extent, microgrid can decrease the construction cost and improve the environment problem. Reliability assessment of distribution system with microgrid is studied in this paper.The radial structure of traditional distribution system is been changed greatly when microgrid connects with distribution system. When microgrid connects with distribution grid, it turns out to be a network that includes multiple sources and loads. As a result, the operation reliability of distribution network is improved significantly. When a fault occurs in distribution system, microgrid can disconnect from the grid connection to ensure the normal and stable operation of the loads in the microgrid. Microgrid is able to connect with distribution system with the use of PCC when the fault is eliminated. Microgrid can switch seamlessly and flexibly between grid-connected and islanded state. Moreover, the output power of micro power is random and intermittent, which makes the reliability assessment of distribution system with microgrid more complex. So the model and methods of reliability assessment of traditional distribution network should be changed accordingly.The concept and construction of microgrid as well as the principle of various distributed generators in microgrid is summarized according to the research status of microgrid at home and abroad at first in the paper. Then two kinds of operation modes and several control methods of microgrid is introduced based on the components in microgrid. The quality of voltage and frequency of microgrid can keep stable with the reasonable control strategies and microgrid can operate stably and reliably. Then the reliability index of load and system, model of reliability assessment of facility and methods of reliability assessment of conventional distribution system is introduced. And according to the simulation and calculation of IEEE BUS6 system with the help of time-sequential Monte-Carlo method, the results verify the accuracy of the method.In addition, research about microgrid which operates in an islanded mode is carried out applying HOMER software with illustrative examples, and the results contrast with the obtained results using analytical method proves the improvement of reliability and economy when microgrid operates in islanded state. In the end, wind speed is simulated based on maximum entropy principle and light intensity is simulated using ARMA model. Then the reliability model of WT and PV is obtained according to their power characteristic curve. Finally, the model of reliability assessment of distribution system with microgrid is established and the simulation results of improved IEEE BUS6 system analyze the impact of access point of microgrid and intermittent of DG to the reliability, which proves that microgrid can improve the operation reliability of distribution network with the help of time-sequential Monte-Carlo simulation. This paper has a significant impact on the planning of microgrid and it is helpful for improving the operation reliability of distribution system with microgird. |
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