A Novel Modal Representation of Battery Dynamics

Khaled I Alsharif,Eric Macdonald,Kyosung Choo,Vamsi Borra,Pedro Cortes,Frank X Li,Alexander H Pesch

doi:10.1109/access.2022.3149617

Abstract

Electrochemical cells are complicated energy storage systems with nonlinear voltage dynamics. There is a need for accurate dynamic modeling of the battery system to predict its behavior over time when discharging. The study conducted in this paper developed an intuitive model for electrochemical cells based on a simple mechanical analogy. A three-degree-of-freedom, spring-mass-damper system was decomposed into modal coordinates that represent the overall discharge, mass transport, and double-layer effect of the electrochemical cell. The developed model was experimentally demonstrated through pulsed discharge tests of commercially available lithium-ion and nickel metal hydride cells. The modal parameters of the natural frequency and damping ratio for each mode were determined by numerically minimizing the error in the time responses. Additionally, the mechanical analog was applied to two datasets developed by the Center for Advanced Life Cycle Engineering (CALCE). The first dataset was used to optimize the modal parameters whereas the second dataset was utilized to validate the tuned parameters. It was found that the modal representation of the mechanical analog could accurately predict the time-response dynamics of all the cells considered. Additionally, by considering the discharge modal coordinate, the open-circuit voltage was determined and validated to that measured experimentally from the voltage relaxation peaks.

Highlights

Electrochemical cells for energy storage are becoming increasingly important in the industry and everyday life [1] – [3]
The effects due to the mass transfer and the double-layer were predicted by the model and displayed, along with the OCV estimation of the batteries
The study conducted in this paper proposed a novel mechanical analog to predict the nonlinear behavior of a battery in modal coordinates

Summary

INTRODUCTION

Electrochemical cells for energy storage are becoming increasingly important in the industry and everyday life [1] – [3]. To conveniently and effectively measure the current and voltage responses across the battery, the experimental setup shown in Fig. 6 is employed This single-loop circuit is constructed from a DC power supply (Keysight E36312A) as a discharger of constant current, a relay to control when the current is applied to the battery in the circuit, and a waveform generator (Keysight 3360A) to produce square waves that trigger the relay at a set frequency. The current load profile allowed the battery to rest until the relaxation period reached steady state; the OCV-SOC relationship was established This dataset was used to tuned and optimize the modal parameters to fit the output system response, Vout, to the measured terminal voltage. This neglects any minor remaining transient to steady state due to the frequency and duty cycle that generated the current load. Good agreement is found, indicating that the modal representation may be useful as an OCV estimator

Duracell Nickel Metal Hydride Battery

Samsung INR 18650-20R Battery

CONCLUSION