Abstract
This paper proposes a charge-allocable charger for series-connected batteries with a bidirectional flyback converter that is capable of switching voltage polarity. The converter provides additional charging current to the lowest state-of-charge (SOC) battery module or discharge the highest SOC battery module. For extremely unbalanced SOC profile, the individual charging for specific module can be performed and therefore, more charge can be replenished into the battery pack. Experimental tests are carried out upon five series-connected battery modules, which consist of 8 lithium-iron phosphate (LiFePO4) battery cell in each module. The charge balancing strategy is developed according to the LiFePO4 battery loaded voltage profile pattern. Experimental results show that the proposed circuit can postpone the instant that high-SOC battery reaches the cut-off voltage, extending the charging time for entire battery pack. For battery modules with large initial voltage discrepancies, the final battery modules voltage difference can be reduced to about 80 mV as the best result.
Published Version
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