A Modular Battery Voltage-Balancing System Using a Series-Connected Topology

A new modular topology and control method is presented for balancing the voltages of a series-connected string of battery cells. The proposed topology has fewer components compared to similar methods and is characterized as “cell to string to cell” category since charge transfer occurs between all cells during a cycle: this increases the speed of the charge equalization process. Two battery cells are connected to a bridge module and bridge modules are connected in series through transformer tertiary windings. This series connection causes all bridges to have the same effect on each other and makes the system operation and analysis more predictable. As waveforms and transferred charge can be predicted accurately through analysis, the equalization time is also optimized through a design procedure. The easy-to-implement distributed controller described requires only one voltage sensor per two battery cells.