A Novel Method to Balance and Reconfigure Series-Connected Battery Strings

Cell failure and imbalance are critical problems in battery storage systems, especially in series-connected battery strings. The reconfiguration function and the balancing function are both of great importance, but it is very challenging and problematic to own both functions simultaneously. This paper attempts to make contributions on realizing both functions through new circuits and new control strategies. Firstly, a reconfigurable balancing circuit is proposed, which is able to simultaneously balance and reconfigure the battery string. In the circuits, a new way to achieve passive balancing with no bleeding resistor is realized, and the failure cells in the battery string can be bypassed with the same circuits. By taking advantage of fewer switches in the circuits, the method owns the merits of low cost and low system complexity. Secondly, to efficiently balance and reconfigure the battery string, a control strategy is proposed according to the unique structure of the circuits. Thirdly, the reconfigurable balancing circuits are fabricated and an experimental test workbench is established. The reconfigurable balancing circuits and the control strategy are validated in the experimental test workbench. The experimental results indicate that the proposed method is able to realize both the balancing function and the reconfiguration function well, and the performance of the battery string can be maintained and improved significantly. The improvements are 13% and 34% for 4 cell- and 100 cell- series-connected battery strings, respectively.