Integrated converter network for active balancing structure of battery

Energy storage systems are critical elements in Plug-In, hybrid and full electric vehicle (EV, HEV, and PHEV) applications. In these systems, lithium-ion (Li-Ion) batteries are now preferred for their outstanding characteristics and advantages. For high voltage applications, battery cells are connected in series, raising the issue of voltage and charge balancing among the cells. This paper presents a new topology that uses modular highly integrated dc-dc converters to perform active balancing. The proposed modular architecture, which enables a real time balancing of all cells, can be used for any number of cells connected in series. It does not require control communications between the converters, and naturally distributes the energy among the cells according to their state of charge (SOC) and capacity data, extracted from the associated Battery Management System (BMS). Design and control details are provided for low-voltage, low-power dual active bridge (DAB) power converters. They have been selected as converter modules for their high compliance to the hybrid integration criteria such as reduced number and value of passive components, monolithic integration of the active devices and ease of driving control. Experimental results are presented for four series connected 3.2V 10Ah Li-Ion battery cells balanced by three DAB converters embedded onto the commercial BMS.