Application of the Pseudo-Random Impulse Sequence Generator for Impedance Measurement of Lithium-ion Cells

The internal impedance of a battery can be used to evaluate the capacity and health of a Li-ion battery as well as provide information for battery modeling. This impedance can be measured using electrochemical-impedance-spectroscopy where the cell is perturbed by a sinusoidal signal at discrete frequencies or by using broadband perturbation signals such as pseudo-random-sequences. This paper discusses the design considerations for the pseudo-random impulse sequence generator for the Li-ion battery impedance measurements. The effects of the various parameters such as the series RLC circuit parameters and the input DC voltage on the perturbation signal are evaluated through simulation and a laboratory experiment respectively. It is shown that the capacitor can be tuned to improve the low-frequency characteristics of the perturbation signal while the inductor can be used to control spectral characteristics in the higher-frequency band. The resistance and input DC voltage, on the other hand, control the overall magnitude of the perturbation signal spectral energy.

I. Introduction

Lithium-ion (Li-ion) battery energy storage systems (BESS) are increasingly vital for integrating renewable energy sources like solar and wind into the electrical grid. The Li-ion cells, however, require thorough characterization and optimization for effective battery management. The internal broadband impedance of a Li-ion battery can provide useful information regarding the available capacity through the state of charge (SOC) and state of health (SOH) [1]–[3]. Furthermore, this impedance can be used to develop suitable battery models through parameter estimation studies. Measurement of this impedance typically involves perturbing the battery cell with a suitable perturbation signal and recording the excitation voltage and current response signals over a time interval. Impedance is then computed from these response waveforms. The perturbation signal can have a notable effect on the accuracy of the computed impedance. An important consideration in the impedance measurement is that the perturbation signal induces persistent excitation of all the relevant modes of the battery cell.