Design and control of an integrated BMS/DC-DC system for electric vehicles

Electric-drive vehicles require a battery management system (BMS) for normal, safe operation of the battery pack, and a DC/DC converter to supply auxiliary loads on the low-voltage (LV) DC bus. This paper presents a shared, central control approach for an integrated BMS/DC-DC system that uses modular DC/DC bypass converters to achieve battery management and supply auxiliary loads in electric vehicles. The motivation to integrate the BMS and DC/DC is to provide differential control of battery cells using the LV bus load and provide an opportunity for advanced battery management to achieve longer battery life and higher power limits. The proposed control approach, system modeling, loop gain analysis, and design of the feedback compensators are provided. Experimental results are presented for a prototype system consisting of eighteen series connected 25 Ah lithium-ion NMC battery cells and three isolated dual-active bridge bypass converters, with combined outputs rated to supply a 1.44 kW auxiliary LV load.