Optimal Allocation of BESS to Maximize Efficiency Under Constrained SOC in Parallel Inverter-Based Scaled-Up Slack Bus

The parallel inverter-based scaled-up slack bus includes multiple battery energy storage systems (BESSs) to support the slack operation without short of real power. The multiple BESSs require a well-designed state of the charge (SOC) balancing algorithm for maximally effective usage. Until now, however, the SOC balancing algorithms only focus on strong SOC balancing without careful consideration of BESS efficiency during its charging and discharging. This paper proposes a soft SOC balancing algorithm based on the Levenberg-Marquardt (L-M) algorithm considering BESS’s charging and discharging efficiency. The charges or discharges of the BESSs are primarily determined by their efficiencies that indirectly reflect the SOCs. As a result, the proposed method provides some margins to improve efficiency rather than tightly focusing on only the SOCs balancing between multiple BESSs (e.g., two BESSs with 0.7 and 0.4 pu of SOCs discharge rather than only one BESS with large SOC discharges when total output is 0.86 pus). The optimizations and balancing are conducted by MATLAB software. Their related converter interactions are simulated using a power system computer-aided design/electromagnetic transient including DC (PSCAD/EMTDC $^{\mathrm {TM}}$ ), to measure data for optimization.