Stand-alone micro-grids need a proper management of the active power exchange. This work is focused on the parallel operation of multiple grid-connected converters in an island-grid system. The proposed solution features a master inverter which emulates the grid and multiple grid-connected converters operating in parallel. The current sharing and overload protection is achieved by small frequency variations of master inverter's output, that are detected by the grid-connected converters. This mechanism exploits the behavior of the derating characteristics embedded in grid-connected inverters, that must reduce the output power if the grid frequency increases. In this case, standard grid-connected equipment can be used to realize micro-grids without the need of digital communication between the power units. Two possible scenarios are analyzed: low-power microgrid with master/slave converters, and low voltage grid fed by a Smart Transformer (ST) which performs the frequency control.
Frequency-based control of a micro-grid with multiple renewable energy sources / Buticchi, Giampaolo; Liserre, Marco; Barater, Davide; Concari, Carlo; Soldati, Alessandro; Franceschini, Giovanni. - (2014), pp. 5273-5280. (Intervento presentato al convegno 2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014 tenutosi a Pittsburgh Convention Center Pittsburgh, PA, USA nel 14 Sep - 18 Sep 2014) [10.1109/ECCE.2014.6954124].