Small-Perturbation Electrochemical Impedance Spectroscopy System With High Accuracy for High-Capacity Batteries in Electric Vehicles

This article presents an electrochemical impedance spectroscopy (EIS) system optimized for high-capacity electric vehicle (EV) batteries, prioritizing high measurement accuracy with minimal current perturbation while reducing measurement time. The system incorporates a switched-resistor high-pass filter for accurate ac voltage measurement and a low-noise amplifier for signal amplification. It also features two parallel low-pass filters with tailored bandwidths (0.2 Hz for 1–9 Hz and 1 Hz for 10–1 k Hz), significantly enhancing accuracy and reducing settling time. In addition, the small current perturbation approach improves safety and simplifies the analysis process. Our prototype achieves precise impedance measurement with a standard deviation of less than 10.4 $\boldsymbol{\mu}\boldsymbol{\Omega}$ for high-precision resistors and less than 14 $\boldsymbol{\mu}\boldsymbol{\Omega}$ root-mean-square error in magnitude for a 70 Ah battery across 1–1 k Hz frequency range and 20–80% state-of-charge range at 25${}^{\circ}\text{C}$ temperature. These findings demonstrate the proposed EIS system's effectiveness in the accurate assessment and health monitoring of large EV batteries.