In the application of long series batteries

there is always the phenomenon that multiple cells in a pack are unbalanced simultaneously. In view of this situation

a mode-varying cell equalizer topology based on interleaved parallel multiple transformers is proposed in this paper. Every unit in this equalizer can freely switch between LLC resonance mode and 3-state LC quasi-resonance mode. The boosting effect of LLC structure is used to reduce the number of transformer's total turns. When multiple equalizer units need to work in LLC mode simultaneously

interleaved parallel technology is used to limit secondary side equalization current ripple for long-term protection of battery life. A prototype was designed and built to validate the effect of a closed loop LLC mode control algorithm with a state-of-charge (SOC) based equalization scheme selection strategy. Experimental results including up to 88.52% efficiency in LLC mode with 90.7% efficiency in 3-state LC mode

and minute level balancing time show the proposed topology demonstrates excellent balancing performance.