PV-fed multi-output buck converter-based renewable energy storage system with extended current control for lifetime extension of Li-ion batteries

Recently, there has been a visible intensification of research on increasing the cycle life of energy storage devices used in Photovoltaic (PV)-fed energy storage systems (ESS). Compared to existing battery technologies, Lithium-ion (Li-ion) batteries have advantages such as high energy density and high cycle life. However, many existing Hybrid energy storage system (HESS) suffers from the fact that Li-ion batteries have limited cycle life, calendar and cycle aging. Therefore, attention has shifted towards the charging techniques necessary to improve the service life of Li-ion batteries by increasing their cycle life and reducing capacity losses. One such approach is to charge the battery by gradually increasing it from a certain level, rather than starting the charging process directly with the maximum charging current. This study proposes Extended Current Control (ECC) to reduce battery capacity losses and extend service life in PV-fed HESSs. The maximum power point (MPP) of the PV module is provided by the Perturb and observe (P&O) algorithm via the supercapacitor (SC) converter, while ECC is performed via the battery converter. This approach requires less hardware, unlike optimization, rule, or filtering based techniques. Controlling the battery current over a large area protects the battery packs from high currents at the start of charge and reduces capacity losses by increasing cycle life. Compared to PV-fed ESS containing only battery packs, the proposed technique provides a 40 % improvement in battery charging current, an 8 % improvement in the converter duty ratio in reaching the MPP point, and a 31.69 % improvement in battery capacity fades.