A Series-Port Voltage High-Precision Self-Balancing Circuit for Active Balancing of Battery Packs

Active balancing circuits of series-connected battery packs commonly involve a trade-off between switch count and achievable voltage equalization accuracy. Balancing circuits aiming for high precision often require a prohibitive number of active switches, whereas those with reduced switch counts frequently fail to meet stringent practical accuracy requirements. This paper proposes a series-port voltage high-precision self-balancing active equalizer derived via a systematic topology derivation approach. The circuit requires only two active switches and uses an auxiliary capacitor to enforce highconsistency adjacent port voltages, enabling self-balancing without complex sensing-driven control. Operating principles and the self-balancing mechanism are analyzed, and key device stresses are derived. Finally, an eight-cell (4 Ah) experimental prototype is constructed to validate the concept under both charging and discharging conditions at 400 kHz with ~30 W balancing operation, achieving a final pack port-voltage deviation of ≤10 mV.