Active balancing system for electric vehicles with incorporated low voltage bus

Electric-drive vehicles, including hybrid (HEV), plug-in hybrid (PHEV) and electric vehicles (EV), require a high-voltage (HV) battery pack for propulsion, and a low-voltage (LV) dc bus for auxiliary loads. This paper presents an architecture that uses modular dc-dc bypass converters to perform active battery cell balancing and to supply current to auxiliary loads, eliminating the need for a separate HV-to-LV high step-down dc-dc converter. The modular architecture, which achieves continuous balancing of all cells, can be used with an arbitrary number of cells in series, requires no control communications between converters, and naturally shares the auxiliary load current according to the relative state-of-charge (SOC) and capacities of the battery cells. Design and control details are provided for low-voltage, low-power dual active bridge (DAB) power converters serving as bypass converter modules. Experimental results are presented for a system consisting of two series 3.6 Ah NMC battery cells and two DAB bypass converters, with combined outputs rated to supply a 12 V, 35 W auxiliary load.