An Internal Resistance Consistency Detection Approach for Lithium-Ion Battery Pack Using Unbalanced Capacitor Current

Lithium-ion batteries (LIBs) are widely used in electric vehicles (EVs). The internal resistance consistency is essential to the performance and safety of LIB packs. To detect the consistency of the LIB cell efficiently, an approach using the unbalanced current is proposed. First, a simple bridging circuit model with four LIB cells is built based on the first-order Thevenin equivalent circuit. Different bridging components are compared to minimize the impact on the LIB system. The capacitor is chosen as the bridging component for the capacity loss less than
$5.5\,\, {}\times {}10^{-8}$
Ah. The characteristics of capacitor current under different inconsistent degrees and initial state of charge (SOC) are investigated when the internal resistance of the cell is inconsistent. The unbalanced current pulse is generated on the bridging capacitor in an inconsistent pack. To accurately localize the cell with inconsistent internal resistance in the LIB pack, an improved bridging circuit is built. The simulation and experimental results indicate that the polarity and amplitude of the bridging capacitor currents could be used to detect and localize the inconsistent cell or region with an average error of 1.33%. The capacity loss is 10−10–10−9 Ah for the LIB pack with eight modules.