A combined Li-ion & lead-acid battery system for start-stop application: potential & realization

Abstract: The aim of this master thesis is to investigate the possibility of using lithium-ion batteries as a second battery instead of lead-acid batteries for the start-stop application in vehicles. To achieve the specified target, the following steps are explored: investigation of the technology market, choice of relevant sizing of the battery, development of charge algorithms for the battery system, creation of an electric simulation model with Simulink, development of a prototype for installation in car and finally verification of the new battery model in a vehicle. The battery which is chosen is a Li-ion battery with a voltage of 16.6V and a capacity of 30Ah due to the test-rig requirements and availability. Before implementation in the vehicle, tests are performed on the battery pack and the combined system. The controller system for charging and discharging is created in Simulink. Through several experiments, the working voltage range of the Li-ion battery pack was defined from 14.8V to 14.2V. In addition, a verification of this solution has been done in a real vehicle. Moreover, comparing the experimental results with our literature study, a new type of lithium-ion battery chemistry, which matches the characteristics required in this work is investigated: a LiFePO4 cathode based battery.