Integrated energy management of solar-powered lithium-ion batteries using fractional open-circuit voltage MPPT and predictive SOC-based passive cell balancing

Lithium-ion battery packs integrated with solar photovoltaic (PV) systems are susceptible to state-of-charge (SOC) imbalance among series-connected cells, which can reduce charging efficiency, usable capacity, and battery lifetime. This study proposes an integrated energy management strategy that combines fractional open-circuit voltage (FOCV)-based maximum power point tracking (MPPT) with predictive SOC-based passive cell balancing for a solar-powered lithium-ion battery system. A 185 W PV module is interfaced with a 13-cell battery pack comprising 3.7 V, 2.6 Ah cells through a boost DC–DC converter. The FOCV-based MPPT regulates the PV operating voltage within 70%–80% of the open-circuit voltage, while the predictive balancing algorithm continuously evaluates individual-cell SOC and selectively activates MOSFET-controlled bypass resistors to reduce SOC disparities. The proposed system is modeled and evaluated in the Typhoon-HIL environment and validated in real time using a Typhoon HIL-402 platform. The system extracts a maximum PV power of 183.95 W and achieves an MPPT efficiency of 98.9%, balancing efficiency of 94.6%, energy-utilization efficiency of 99.2%, and balancing power loss of approximately 0.41 W. The proposed approach also reduces SOC equalization time by 35% relative to the reported baseline. These results demonstrate that the integrated strategy can simultaneously enhance solar energy utilization and improve SOC uniformity in lithium-ion battery systems.