부산대학교 도서관

Voltage equalizer is essential for mitigating the inconsistencies of series-connected lithium-ion batteries in electric vehicles to ensure operation life and work safety. To keep voltage balancing, voltage equalizers are widely adopted in the battery string application. However, traditional voltage equalizers have high circuit costs and large sizes due to the need for a large number of MOSFETs and isolated gate drivers. Moreover, as the voltage difference between the batteries in the series decreases towards the end of the equalization process, the equalization current also decreases, which can affect the speed of voltage equalization. To overcome these problems, an isolated multiple half-bridge converter with a multiport transformer is proposed. The balancing circuit has two power transfer paths, allowing for energy transfer among multiple cells simultaneously, which could achieve a significant equalization current even when the voltage difference is close to zero. In the proposed equalizer, only one MOSFET is needed for one cell and two cells can share one transformer winding. Hence, it is more applicable for a large number of battery stacks, such as electric vehicles. Finally, to improve the equalization speed and efficiency, three equalization control strategies, i.e., average voltage, predicted voltage, and boundary voltage control strategies are introduced and verified by a 100 kHz 24-cell voltage equalization prototype.