A New State-of-Charge Control Derivation Method for Hybrid Battery Type Integration

The hybrid of ex-transportation and conventional new battery system integration has started gaining interests within energy storage systems as number of electric vehicle on-road increases. Each module within such a system may consist of batteries with different charging/discharging rates, characteristics and also different nominal voltage levels. Control of these hybrid batteries within the same system is more challenging compared to conventional battery management systems, which mainly deal with the homogeneous battery system. One of the key issues is how to control the state-of-charge trajectory of the hybrid modules to maximize the investment on the new hybrid battery system. To cater this problem, this paper brings a new rigorous derivation method of state-of-charge control based on converter sample time. The proposed method generates desired current reference in each time step to distribute the power among hybrid modules such that their discharging or charging trajectories finish at the same time. This technique makes sure that the energy delivered/absorbed from each cell in a uniform manner maximizing the overall lifespan. Detailed derivation of the current sharing method and suitable module based adaptive bidirectional control architecture has also been presented. Modeling, analysis, and experimental validations are performed on a three-module-based grid-tie hybrid battery energy storage system prototype to validate analysis.