Control strategies and real time operation of storage systems integrated with MV photovoltaic plants

Nowadays the increasing share of renewable sources requires a direct participation of all form of generation to the secure operation of the electric power system, at least in terms of power balancing and voltage regulation. Resiliency, controllability and flexibility are the key factors that characterize a smart grid, compared to traditional energy systems. In this regard, storage systems can be used to provide the grid with a large range of services, such as frequency and voltage regulation, short-term power reserve and power quality. Nevertheless, persistent power modulation can originate a progressive drift of the battery State of Charge, thus reducing the real exploitability of the storage system for other scheduled energy services, like load levelling. This paper describes in a systematic approach a novel control architecture, in which an external loop aimed to compensate the SOC drift, in addition to the conventional frequency droop regulation, has been implemented and tested on an existing MV photovoltaic plant integrated with energy storage.