SELF-BALANCING SWITCHING CONTROL OF DUAL-PACK RECHARGABLE ENERGY STORAGE SYSTEM WITH SERIES AND PARALLEL MODES

An electrical system includes a rechargeable energy storage system (RESS) and a controller. The RESS includes first and second battery packs connected to a voltage bus, each pack having a respective plurality of battery cells and a corresponding cell balancing circuit. The RESS further includes switches that selectively connect or disconnect the packs to or from each other to achieve series and parallel modes. The controller executes a method by detecting a requested series to parallel mode transition. Responsive to a threshold imbalance being present in a state of charge or pack voltage of the packs relative to each other, the controller balances the state of charge/voltage using open/closed state control of the cell balancing circuits, and possibly a switching block having PWM-controlled switches and a circuit element. The controller may execute the requested mode transition upon balancing.