Automatic charge equalization circuit based on regulated voltage source for series connected lithium-ion batteries

In the lithium-ion batteries for electric vehicle applications, the charge equalizer is required to enhance life time and guarantee safety. For efficient charge equalization, a cell voltage sensing module should be used. However, the cost of the sensing module is relatively high. Thus, to achieve higher equalization performance without the cell voltage sensing module, a new automatic charge equalizer based on regulated voltage source is proposed. A fast regulated voltage source with average voltage of the batteries is implemented by a bidirectional dc-dc converter. The charge equalization can be automatically achieved by periodic connections between battery cells and regulated voltage source without the sensing module. The high equalization performance can be obtained by proposed reference voltage modulation and advanced skip mode. The operational principles and design considerations of the proposed equalizer are presented and equalization performance is verified by the prototype with 7Ah lithium-ion batteries.