Abstract
The impedance of a Lithium-ion (Li-ion) battery has been shown to be a valuable tool in evaluating the battery characteristics such as the state-of-charge (SOC) and state-of-health (SOH). Recent studies have shown impedance-measurement methods based on broadband pseudo-random sequences (PRS) and Fourier techniques. The methods can be efficiently applied in real-time applications where the conventional electrochemical-impedance spectroscopy (EIS) is not well suited to measure the impedance. The techniques based on the PRS are, however, strongly affected by the battery nonlinearities. This paper presents the use of a direct-synthesis ternary (DST) signal to minimize the effect caused by the nonlinearities. In such a signal, the second- and third-order harmonics are suppressed from the signal energy spectrum. As a result, the effect of the second- and third-order nonlinearities are suppressed from the impedance measurements. The impedance measurements are carried out for a nickel manganese cobalt Li-ion battery cell. The performance of the method is compared to the conventional EIS, as well as to other PRS signals which are more prone to battery nonlinearities. The Kronig–Kramers (K–K) transformation test is used to validate the uniqueness of the measured impedance spectra. It is shown that the measurement method based on the DST produces highly accurate impedance measurements under nonlinear distortions of the battery. The method shows a good K–K test behavior indicating that the measured impedance complies well to a linearized equivalent circuit model that can be used for the SOC and SOH estimation of the battery. Due to the good performance, low measurement time, and simplicity of the DST, the method is well suited for practical battery applications.
Highlights
Lithium-ion (Li-ion) batteries have become increasingly important in various portable and stationary electrical energy applications in recent years [1]
This paper demonstrates the use of the DST sequence with suppressed harmonic multiples of two and three for impedance measurements of a nickel-manganese-cobalt Li-ion battery
The increased performance of the DST sequence over other pseudo-random sequences (PRS) can be concluded as it has the best match to the EIS results and it has the smallest deviation compared to the MLB and QRT sequences
Summary
Lithium-ion (Li-ion) batteries have become increasingly important in various portable and stationary electrical energy applications in recent years [1]. This is due to their high energy and power density and constantly reducing prices. The battery state is typically characterized in terms of state parameters, such as state-of-charge (SOC). State-of-health (SOH), which are typically estimated from battery voltage, current, and temperature measurements [2,3]. The battery AC impedance has been shown to provide valuable information about the SOC and SOH of the battery [3,4]. The method is very accurate and reliable due to its high
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