Intentional Microgrid Island Operation

The deliberate, planned state in which a microgrid (a local assembly of generation, storage and load, such as an industrial estate with PV, battery storage and a CHP installation) electrically disconnects from the public grid and continues to supply itself independently, with its own voltage and frequency control — a state explicitly different from the unwanted, unintentional islanding that anti-islanding protection of PV inverters is specifically designed to prevent. To operate safely and stably in intentional island mode, at least one source within the microgrid must be able to act as a 'grid-forming' element (actively regulating voltage and frequency instead of merely injecting current onto an already-present grid voltage, as most PV inverters do), and the transition to and from grid-connected operation must follow a defined switching sequence and synchronisation check to prevent damaging inrush currents or phase mismatches. Applications are found mainly at critical facilities (hospitals, data centres) and in grid-congestion areas where island operation can temporarily provide relief, but protection settings, earthing philosophy (the star point may need to be locally re-formed during island operation) and selectivity must be calculated separately for both operating states.