Individual cell voltage equalizer using selective two current paths for series connected li-ion battery strings

This digest proposes an individual cell voltage equalizer using selective two current paths for series connected lithium-ion battery strings. In the proposed equalizer, a central equalization converter is shared by every battery cells through the cell selection switch, instead of a dedicated charge equalizer for each cell. The central converter is utilized as a controllable current source by a modified rectifier. With this configuration, although the proposed equalizer has a central dc-dc converter, individual charge equalization can be effectively achieved for the each cell in the strings. Furthermore, great size reduction and low cost can be obtained for an industrial battery equalizer. In this digest, an optimal power rating design guide is also employed to obtain a minimal balancing size while satisfying equalization requirements. A prototype for eight lithium-ion battery cells is optimally designed and implemented. Experimental results verify that the proposed equalization method has good cell balancing performance.