Defining control strategies for photovoltaic reconnection in islanded microgrids

The increasing integration of photovoltaic systems in recent years challenges power systems with respect to their reliability, security and stability. Frequency stability is one specific problem. Sudden disconnects or connects of large amounts of photovoltaic systems without explicit countermeasures may result in substantial decrease or increase of the power system’s frequency. This can cause load shedding actions, disconnection of other generating units, or, as worst case, a black-out. These problems which occur after the disconnection and connection of photovoltaic systems are even more severe within islanded microgrids, because frequency changes quickly when there is a power mismatch due to their low system inertia. In this paper, an islanded microgrid, including a conventional generator, a photovoltaic array and a lumped load, is used as a study case to investigate the reconnection challenges of photovoltaic systems in those electrical networks with relative low inertia. Four different control scenarios, which regulate the strategy for photovoltaic reconnection, and their communication requirements are described, analyzed and compared.