Proposal of Grid-Forming and Grid-Feeding Converter Control for Transition of AC Microgrid Operating Modes

Primary controls for performing the transitions between grid-tied mode (GTM) and islanding mode (ISM) of an AC microgrid ( MG) are proposed. The MG includes a grid-forming (GFR) unit with a battery pack, and a grid-feeding (GFD) unit with a photovoltaic (PV) array. For GFR and GFD, control schemes are proposed. To design the inner current loop, for the GFR in GTM, Takagi-Sugeno (TS) models and Linear Matrix Inequalities (LMI) are used; whereas, for the DC voltage regulation, the outer loop PI controller is tuned with LMI. For forming the AC voltage at the Point of Common Coupling during ISM, an inner loop LMI controller is used. For the GFD output current control in GTM, an inner loop TSLMI controller is used; and for the maximum power point tracking (MPPT), an outer loop PI controller is used; conversely, to provide the power demanded by the load without complex PV power management algorithms, during ISM, an outer loop PI controller is used. The results showed a good performance of the PI and LMI controllers for the correct MG operation during the transitions, under temperature and irradiation variations, and during load changes.