MMC-PV System with dc-link integrated battery energy storage system

Renewable energy sources, such as photovoltaic (PV) panels, are spreading day by day. Nevertheless, their intermittent and uncertain generation can be an issue for the connection in the electrical grid or for self-consumption. In order to face these problems, battery energy storage systems (BESSs) are used to store the energy in excess and deliver it when required. With and without the integration of BESSs, many solutions to interface PV panels to the grid are analyzed and proposed in the literature. Focusing on the PV power extraction, several maximum power point trackers have been analyzed, also facing the issue related to the partial shading conditions. In fact, the latter can cause inefficiency in maximizing the power extraction when many PV panels are subjected to different irradiations. Modular multilevel converters (MMCs) are recently used even in low voltage systems for their intrinsic advantages. In particular, PV panels and BESSs can be integrated into the MMC at either the submodule level or the dc-link of the MMC itself. Taking the advantages of both kinds of connection, in the present paper, a three-phase MMC with PV panels integrated into its submodules and a battery pack connected to its dc-link is proposed and analyzed.