Online impedance spectroscopy estimation of a dc–dc converter connected battery using a switched capacitor‐based balancing circuit

Dani Strickland,Mina Abedi Varnosfaderani

doi:10.1049/joe.2018.8069

Abstract

This study investigates a novel method of undertaking online electrochemical impedance spectroscopy measurements to estimate battery impedance across the frequency range using a battery balancing circuit. A switched capacitor balancing system is used to generate an excitation signal of low-frequency of variable values from which battery voltage and current can be measured to estimate the impedance.

Highlights

Electrochemical impedance spectroscopy (EIS) is a method of determining impedance across a frequency spectrum to try and understand electrochemical behaviour in a test piece such as a battery
As the battery current and voltage are a function of the boost converter current and the current caused by the battery balancing circuit, the low-frequency component of the measured current needs to be extracted using Fourier transforms
This study presented an analysis and implementation of a method of inducing a low-frequency excitation signal in hardware using battery balancing hardware

Summary

Introduction

Electrochemical impedance spectroscopy (EIS) is a method of determining impedance across a frequency spectrum to try and understand electrochemical behaviour in a test piece such as a battery. A standard switched capacitor balancing system is designed and sized to generate the low-frequency excitation signal needed for EIS measurement and analysis. The capacitor and switches M1–M4 were operated to balance the batteries while at the same time producing a low-frequency excitation signal. As the battery current and voltage are a function of the boost converter current and the current caused by the battery balancing circuit, the low-frequency component of the measured current needs to be extracted using Fourier transforms. While the current on the battery with the lower voltage decreases with each low-frequency switched period when connected to the capacitor as the capacitor is used to offset the boost converter current and charge the battery. Its impedance increases (resulting in a reduced τ) leading to a less accurate calculation

Modelling

Experimental result

Conclusions