Skip to Main Content
Unlike conventional utility grids, microgrids comprise generators, storage devices and loads at all levels of the system. Power generation, distribution and consumption levels are not discrete and power flow may occur at any direction. At any point in time, microgrid may be disconnected from the utility grid and continue its operation under islanding conditions. Furthermore, some microgrids may have changing structures with alternative paths and the coupling point for a device or a part of the microgrid may change due to the altering conditions. Considering all of these challenges, it is required to develop a new protection concept/scheme for a safe and secure operation. Maintaining proper selective operation of relays in these new systems and new dynamic microgrid structures is also a challenge in itself. This requires monitoring the connections and updating time delays of the relays to ensure the desired protection hierarchy in the system. In this paper, a microgrid system is modeled according to the graph theory where the components are represented as nodes. Dijkstra's algorithm, which is famous for shortest-path calculation purposes, is run over the microgrid to determine the relay hierarchy at any point in time. In this manner, regardless of the dynamic changes occurring in the system the hierarchy of network components can be extracted. The implemented algorithm not only ensures proper selective operation under fault conditions but also facilitates the introduction of new connections and new devices to the system. Since the relay hierarchy is detected automatically, even with new connections, this algorithm serves for plug-and-play concepts in electrical networks.
Date of Conference: 17-20 Oct. 2011