Energy management of a battery energy storage system integrated with grid-connected solar power

With the increasing integration of renewable energy sources into modern power systems, there is a growing demand for advanced grid-connected power conversion structures capable of ensuring high power quality, operational reliability, and system stability under various operating conditions. This paper investigates an integrated, transformerless power conversion architecture based on an H-bridge neutral-point-clamped (H-NPC) inverter, in which a photovoltaic (PV) system and a battery energy storage system (BESS) operate through a common DC-link. On the DC side, a bidirectional DC–DC converter is incorporated to enable controlled charging and discharging of a lithium-ion battery pack. The PV array is interfaced with the DC-link via a boost-type DC–DC converter operating under a perturb-and-observe (P&O) maximum power point tracking (MPPT) algorithm. On the AC side, sinusoidal grid current injection with low total harmonic distortion (THD) is achieved by employing an LCL filter and a sliding-mode-control (SMC)-based current control strategy. The proposed system is evaluated under various operating conditions, including rapid irradiance variations, sudden load changes, and complete loss of PV power generation. Simulation results demonstrate that the proposed control framework effectively regulates the DC-link voltage, ensures seamless power flow between the PV and the BESS, and maintains high-quality grid current under all investigated scenarios. Even in the absence of PV power generation, continuous energy supply to the grid is sustained through the BESS, highlighting the effectiveness and robustness of the proposed integrated framework for grid-connected renewable energy applications.