Battery Impedance Measurements at Nonstationary Conditions using DFT Eigenvector Perturbations

This paper demonstrates the use of quadratic-residue-ternary (QRT) sequence, along with its binary approximation, the quadratic-residue-binary (QRB) sequence for Li-ion battery impedance measurements at nonstationary conditions created by DC charging/discharging currents. The QRT sequence is a full eigenvector of the discrete Fourier transform and these properties are also conveyed to the QRB sequence with certain conditions. The discrete Fourier transform eigenvector properties can be effectively used to cancel out the corruptive effects of the voltage drifts during nonstationary conditions. The demonstrated sequences have not been previously used in practice for the purpose and especially the QRB sequence can have significant practical potential for dynamic EIS because of its binary waveform.