Online Internal Impedance Measurements of Li-ion Battery Using PRBS Broadband Excitation and Fourier Techniques: Methods and Injection Design

Abstract

The internal impedance of a battery has been shown to vary as a function of state-of-charge (SOC) and state-of-health (SOH) which are important parameters defining the battery conditions in Li-Ion batteries. Therefore, the online monitoring of the internal impedance can be used as a useful SOC- and SOH-estimation parameter in battery management systems. Recent studies have shown methods based on broadband injections which make it possible to perform rapid Li-Ion battery impedance measurements. The studies have not, however, fully considered the properties of the applied injections nor the applied computation methods. This work extends the studies, and presents systematic steps for designing an excitation signal for battery internal impedance measurements. A pseudo-random binary sequence (PRBS) is applied and the internal impedance is obtained through Fourier techniques. The presented methods can be used for rapid and accurate impedance measurements, and thus, as a valuable online tool in SOC- and SOH-estimation algorithms. Practical measurements are shown from a commercial nickel-manganese-cobalt (NMC) Li-Ion battery.