Crosstalk compensation for a rapid, higher-resolution impedance spectrum measurement

Abstract

Abstract-CrosstalkCompensation is an approach that enables rapid, higher-resolution impedance spectra measurements of energy storage devices. The input signal consists of a sum-ofsines excitation current that has a known frequency spread. The advantage of Crosstalk Compensation is that high resolution spectra can be acquired within one period of the lowest frequency while also including non-harmonic frequencies. The crosstalk interference at a given frequency can be pre-determined and assigned to an error matrix. The real and imaginary impedance can then be calculated based on the inverse of the error matrix and captured response. Analytical validation of Crosstalk Compensation was performed using a battery equivalent circuit model. Two different frequency ranges were simulated, and both indicated that a minimum step factor between frequencies should be 1.25 to reduce the error in compensating the captured response signal. For a frequency range of 1638.4-0.1 Hz, for example, a maximum of 45 frequencies should be included within the excitation signal to accurately acquire the impedance spectra at high resolution. A simplified derivation of Crosstalk Compensation and its corresponding analytical validation studies are discussed.

Determination of Battery Stability with Advanced Diagnostics

“…Recent work has also used EIS to examine the changes in cells in light to moderate levels of abuse. Love et al have examined the impact of overcharge on the single frequency impedance of single cells [21] as well as 4 cell series strings [22].This was able to find a measurable shift in the 500 Hz impedance data as a cell was overcharged up to 135% total SOC. Single frequency impedance such as this has the advantage of being easily integrated into a system as it does not necessarily require costly hardware or computing analysis, and also at higher frequencies can be measured very quickly to provide a real time measurement.…”

“…A typical Nyquist curve measured from a commercially available lithium-ion cell is shown in Figure 6. The high frequency tail on the left side of the spectrum at frequencies greater than 251.2 Hz typically captures equipment artifacts [22] and is not shown in this figure. The point at which the high-frequency tail crosses the real axis is the ohmic resistance (R O ) within the battery, which includes the effects from the electrolyte, electrodes, tabs, etc.…”

Determination of battery stability with advanced diagnostics

“…Recent work has also used EIS to examine the changes in cells in light to moderate levels of abuse. Love et al have examined the impact of overcharge on the single frequency impedance of single cells [21] as well as 4 cell series strings [22].This was able to find a measurable shift in the 500 Hz impedance data as a cell was overcharged up to 135% total SOC. Single frequency impedance has the advantage of being easily integrated into a system as it does not necessarily require costly hardware or computing analysis.…”

“…A typical Nyquist curve measured from a commercially available lithium-ion cell is shown in Figure 4. The high frequency tail on the left side of the spectrum at frequencies greater than 251.2 Hz typically captures equipment artifacts [22] and is not shown in this figure. The point at which the high-frequency tail crosses the real axis is the ohmic resistance (R O ) within the battery, which includes the effects from the electrolyte, electrodes, tabs, etc.…”

“…Various rapid-impedance spectrum measurement techniques have been developed to yield high resolution data comparable with standard, COTS equipment (i.e., multiple data points within the impedance spectra). Harmonic compensated synchronous detection (HCSD) is an example of rapid, lower resolution impedance measurement technique [22,24,25]. The sum-of-sines excitation signal consists of frequencies that are separated by octave harmonics so as to eliminate the effects of crosstalk interference.…”