Active Cell Balancing of Lithium-ion Battery Pack Using Dual DC-DC Converter and Auxiliary Lead-acid Battery

•Coupled inductor-based fly-back converter topology is used for cell balancing during charging•Single Inductor based Buck-converter is used for cell balancing during discharging•Cell voltage and SOC based control logics are developed for the proposed cell balancing scheme•Cell SOC-based control algorithm is found more effective in terms of balancing speed•An Auxiliary lead-acid battery is introduced to supply balancing energy which reduced the requirement of circuit components The effective capacity of lithium-ion battery (LIB) pack is reduced by the inconsistency of individual LIB cell in terms of capacity, voltage and internal resistances. Effective cell balancing scheme not only improves the charging and discharging capacity but at the same time it ensures the safe, reliable and longer operational life of the LIB pack. In this study, a dual DC-DC converter based active cell balancing topology is proposed with reduced number of active components and power switches. Fly-back DC-DC converter-based topology is used for pack to cell (P2C) balancing during LIB pack charging period whereas an auxiliary lead-acid battery to LIB cell balancing is realized by employing a Buck-converter topology during discharging period. Series of simulation studies are conducted in MATLAB-Simscape environment to assess the effectiveness of the proposed cell balancing topology. Cell voltage-based and cell SOC-based control logics are developed using MATLAB-Stateflow diagram for controlling the proposed active balancing topology. All results supported that the proposed circuit can implement an effective balancing operation during both charging and discharging period. A comparison between cell voltage-based and cell SOC-based control logics demonstrated that the SOC based control logic is more effective in terms of balancing speed. The use of auxiliary lead-acid battery for providing balancing energy during discharge period reduced the number of active components, power switches, control complexity, speed and life of LIB pack as P2C balancing is eliminated. The energy generated from regenerative braking can be used for charging the auxiliary lead-acid battery which will further improve the balancing efficiency when the cell balancing topology will be used in electric vehicle applications.