Control strategies for Multi-Microgrids islanding operation through Smart Transformers

•Development of a new control framework using Smart-Transformers (ST) for Multi-Microgrid (MMG) systems in islanding operation.•Smart Transformer with two configurations: a) with a storage unit in DC link and b) without storage at the DC link.•Smart Transformer with a storage unit in the DC link assumes a central role as the enabler of the MMG islanding operation.•Without storage, the Smart-Transformer emulates a grid-forming unit for the LV side and a grid-feeding inverter for the MV side.•A new vision on how to operate in islanding mode an MMG with STs, as wells as proper models to include those devices in the dynamic simulations.