A New Kind of Balancing Circuit with Multiple Equalization Modes for Serially Connected Battery Pack

An active balancing circuit based on a buck--boost converter is proposed to deal with unbalanced states of battery packs. The proposed circuit has low-frequency bidirectional switches to control the states of inductors, including the connection, disconnection, and short-circuit states. By controlling the states of inductors, many kinds of buck-boost converters can be constructed between adjacent cells or groups of several adjacent cells. The proposed circuit has multiple balancing modes with flexible equalization paths, and different equalization processes can occur simultaneously to shorten equalization time. To improve the equalization performance of the proposed circuit, theoretical calculations are carried out to explore the relationship among different equalization parameters. A balancing strategy is presented to illustrate the sequence of equalization processes. Experiments are performed with a six-cell lithium iron phosphate battery pack under different operating conditions to verify the theoretical analysis.