Modularized Design of Active Charge Equalizer for Li-Ion Battery Pack

A modularized design of an active charge equalizer and a charge equalization algorithm for a Li-ion battery pack are proposed in this paper. The equalizer consists of one module-balancing circuit and
$M$
cell-balancing circuits, where
$M$
is the number of modules in the battery pack. Each balancing circuit uses an inductor that is placed in a bridge of four bidirectional switches and works as an energy carrier, and uses a cell/module access network that enables energy transfer from one cell/module to another cell or module. The charge equalization between modules can be performed simultaneously with that between cells, so the proposed circuit can significantly reduce the time required to equalize the charges of all cells in the battery pack. The proposed circuit was tested under various charging/discharging conditions for a battery pack composed of four serially connected modules, with four serially connected cells per module. Experimental results show that the proposed circuit and algorithm comprise a good solution to balance a Li-ion battery pack.