Design and Analysis of Interconnected Medium-Voltage Microgrids

Abstract

Microgrid is considered as a competitive solution for capacity shortage mitigation and supply reliability enhancement instead of conventional grid upgrade. To handle these two grid issues, techno-economic analysis needs to be carried out on technology solutions available for microgrid development, including different energy storage technologies and the possibility to interconnect adjacent microgrids. In this thesis, an energy system model is built on the basis of two real mediumvoltage local distribution grids in Western Sweden. Different scenarios are analysed, including varying requirements on island operation capability and different levels of load expansion. Four technical options, including battery storage system, hydrogen storage system, heat storage system and microgrid interconnection, are provided as technical options for investment. For each scenario, the running result is an optimization solution combining the technical options. The objective of the optimization is to handle all requirements in each scenario with the minimum total cost. The thesis mainly discuss the driving factors that affect the dimension of the four technologies, especially the investment in different energy capacity and power capacity of these technologies. According to the results obtained, individual microgrids mainly rely on battery to manage the grid capacity shortage during periods of high net load. Battery is also the only technology to handle island mode requirement of short durations. However, as the island mode duration increases, hydrogen storage system becomes a complementary solution to the battery storage system for handling the increasing energy storage demand. For interconnected microgrids, there is a reduction on the total net load of the two microgrids because of their complementary net load profile. The interconnection technology is competitive to replace the energy storage technology, especially the hydrogen storage system for long-term and large volume energy back-up.