Enhanced Resolution for Rapid Broadband Battery Impedance Measurements

The inline Rapid Impedance Spectroscopy (iRIS®) sensor provides additional metrics for enhanced battery diagnostics and prognostics. It injects an excitation signal consisting of a sum of sinusoids over a broad frequency range with one period of the lowest frequency and captures the battery response. The existing iRIS sensor is capable of measuring batteries up to 50V having impedance levels down to about $3 \mathrm{m}\mathrm{\Omega}$ with $0.1\ \mathrm{m}\mathrm{\Omega}$ resolution. The measurable battery impedance can be lowered to approximately $1\ \mathrm{m}\mathrm{\Omega}$ with $0.05\ \mathrm{m}\mathrm{\Omega}$ resolution if the maximum iRIS upper voltage threshold is reduced to 15V. Montana Technological University (MTech) has been sponsored by Dynexus Technology to investigate hardware and software solutions for higher resolution capability, improved signal-to-noise ratios, and improved measurement repeatability. Preliminary results show that a cell-level iRIS system (≤5V) can now achieve a resolution of $4.9\mu\mathrm{\Omega}$ ; a 15-V system (e.g., cell strings and sub-modules) can now achieve a resolution of $17.9 \mu\mathrm{\Omega}$ . Another advantage of these upgrades is the ability to measure lower-impedance batteries as well. Measurements to date have been primarily conducted on test cell circuits, which consist of an RC network intended to simulate battery characteristics. Application of these higher resolution measurements, along with repeatability studies, are presented using both test cells and parallel-connected cell strings.