An Active Isolated Battery Equalizer for 24-Cell Based on Soft-Switching Resonant Circuits

Single lithium-ion batteries typically have a lower voltage, so multiple batteries are often connected in series to achieve the required voltage level. To address the voltage imbalance caused by variations between individual cells, a fast active battery equalizer is proposed in this article. Compared to other active balancing circuits, the proposed balancing circuit utilizes a multiwinding transformer, requiring only two magnetic components, and each individual battery is controlled by a single switch, which reduces the circuit cost. Additionally, the proposed converter allows energy exchange between any positions of the battery string through the coordination of two balancing paths. The LC series resonant tank ensures that all switches operate under soft-switching conditions during the balancing process, thereby improving efficiency. Furthermore, a variable group control strategy is introduced to further increase the balancing current magnitude, enhancing the overall balancing speed of the converter. Finally, a 100 kHz resonant frequency, 24-cell voltage balancing prototype validates the effectiveness of the proposed balancing circuit.