A diagnostic function preventing over charging and discharging for a lithium-ion battery management system of electric vehicles

摘要

The paper proposes a diagnostic function to prevent over charging and discharging of the Li-Ion batteries as well as to keep connections with generator and motors of electric vehicles. Both operating conditions normal and abnormal are taken into account in terms of communications. Especially to cope with a situation that communication from the battery side has been cut off, an additional protected function is introduced. The diagnostic function has one generic logic based on the voltage threshold and two layered logics for the unexpected communication situations. First generic logic simply cuts batteries off by monitoring cell voltages. The logic is simply triggered by an upper and lower bound which are the boundary values of the cells' operating range. The other logics, the layered logics are operating when an abnormal communication of the cell voltage monitoring system is detected. The layered logics are based on the battery cell voltage estimation with the first order Thevenin circuit model. In addition, the pack voltages which is measured periodically from a separate circuit board are used to double protect batteries as a redundancy. To apply this estimation logics to the real industrial automotive field, influenceable factors including sensor accuracy and an estimation error are considered on the calculation process. Simulation result is presented to show the effectiveness of the diagnostic function and the estimated cell voltages are compared with real cell voltages as well to prove modeling accuracies.