An Active Direct Balancing Circuit for Series Connected Batteries

The bi-directional cell-to-cell equalization methods perform well to prevent the series connected batteries from overcharging and undercharging. However, it remains a challenge to achieve fast equalization and high equalization efficiency with low complexity. To address the issue, a new direct bi-directional cell-to-cell active equalization method works in continuous current mode (CCM). The new method allows the energy to transfer directly from the source cell to the target one by fly-back operation or Buck-Boost operation which gives a short balancing path and guarantees a fast equalization speed. The experiments with a six-20Ah Lithium-ion battery string are conducted and the results have demonstrated that our new approach has achieved a good overall performance of equalization in terms of speed, efficiency, and complexity of the circuit.