Development of the control strategy for a direct current microgrid: A case study

The widespread use of renewable energy sources, such as photovoltaic plant, has given rise to a growing interest in direct current microgrid. This paper presents the control strategy developed for a dc microgrid interconnected to the ac grid through a bidirectional front-end converter and composed of energy storage systems, such as batteries and supercapacitors, programmable load and a Photovoltaic emulator. The control strategy guarantees power sharing among energy storage system and high quality supply both in grid connected and in island operation. Furthermore, the control strategy allows the management of the power exchange between dc grid and ac grid to achieve the respect of technical and economical requirements. In order to realize the aforesaid goals a hierarchical control strategy, in which the first level is based on a decentralized structure, to guarantee the automatic configurability of the control scheme in case of unavailability of one or more devices or in case of failure of communication link, and a secondary and tertiary level are based on a centralized management unit, is proposed. The proposed control strategy has been validated through experimentation on a real DC Microgrid test facility at RSE.