Coordinated State-of-Charge Balancing and Energy Management for a DC Microgrid Under Dynamic Renewable Conditions

This paper presents an energy-management and state-of-charge (SoC) balancing scheme, denoted OEMSS, for a DC microgrid comprising photovoltaic generation, a fuel-cell source, two energy storage systems (ESSs), and six household loads. A demand-driven power-allocation layer first determines whether generation is sufficient, ESS support is required, or priority-based load scheduling must be activated. A supervisory balancing layer then allocates the fleet charging or discharging request by using a capacity-weighted average SoC and separate mode-dependent correction laws. The balancing command is dimensionally expressed as an energy-capacity deviation divided by the control interval and is projected onto the SoC and power limits. A Python simulation driven by recorded generation profiles is used to evaluate four seasonal operating conditions. In the tested equal-capacity case, the maximum inter-ESS SoC deviation is reduced from 18% to 4.8%, synchronization is reached within approximately 2 to 4 h, and simulated over-discharge events are avoided. The reported increase from 45% to approximately 70% is interpreted as a 25-percentage-point increase in the ESS storage contribution rate, rather than an increase in conversion efficiency. During shortage intervals, the retained priority demand is supplied, whereas satisfaction of the original uncurtailed demand is not claimed. A discrete-time Lyapunov analysis gives the nominal convergence condition 0<γb<2, and the online implementation has O(J+K+H) time complexity. The study provides simulation evidence for a simple coordinated allocation rule; hardware performance, battery-life extension, converter-level stability, and global optimality remain to be established.