Direct Active and Inductive Cell Balancing with Integrated Cell Monitoring for Second Life Battery Systems

The presented paper introduces an active battery balancing method with direct energy transfer between any two cells in a stack or module. This method likewise integrates the possibility to measure each cell voltage. The inductive mode allows the equipping of each stack with only one voltage and two current sensors for full individual cell monitoring. The individual cell measurement is required not only for many Li-Ion applications due to their exothermic behaviour, but also for other cell technologies and systems that need to be balanced. For a stack with 12 cells this can result in a reduction of up to 21 voltage and current sensors. Despite the measuring feature, the presented concept includes an active balancing method. This balancing method offers reduced impact on the battery cells while allowing highly efficient energy balancing. The inductive mode balancing strategy allows energetic balancing instead of only voltage based balancing. This energetic balancing allows not only the mixing of cells of different age within a stack, but also the mixing of cell technologies, while utilising its maximal stored energy.