An Active Cell-to-Cell Equalization Method With Transformers for Series Connected Lithium-ion Battery

Cell equalization is fundamental for maximizing the usable capacity of a battery pack and preventing possible hazard conditions. This paper presents a bi-directional DC/AC converter equalization topology for electric vehicles or high-capacity energy storage systems that employs an active equalization structure with planar transformers to equalize the voltage between high-capacity lithium-ion batteries. The circuit allows direct energy transfer among any cell in flyback mode without the need for individual voltage acquisition. The method provides a shorter equalization path, ensuring fast equalization speeds. Compared with conventional battery management techniques, the method improves the equalization accuracy of each cell, reduces energy loss, and improves the equalization efficiency while reducing the equalization time. Numerical and experimental results confirm the effectiveness and potential of the proposed method.