ORCID Identifier(s)

0000-0001-8046-3109

Graduation Semester and Year

2018

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Department

Electrical Engineering

First Advisor

David A Wetz

Abstract

The United States Navy is considering Li-ion batteries for use as a primary power source for future naval shipboard pulsed-power applications. To supply sufficient power to a load, electrochemical cells are connected in series and parallel to create a higher voltage and higher capacity battery. The simplest way of connecting multiple cells in parallel is to tie all positive terminals together, all negative terminals together, and then electrically treat the array of cells as a single cell within the larger battery. In this configuration, a single battery management system (BMS) can be used to manage N parallel cells but there is no monitoring of each ‘cell’ comprising the parallel array allowing for current imbalances to occur among the N cells. The varying ESRs of the parallel cells can create uneven current sharing, which is compounded by different resistances among the tabs used to connect the cells and subtle manufacturing differences. Current imbalance could negatively impact individual cell lifetimes as well as the array’s safety. The magnitude of this effect in highly paralleled arrays has not been thoroughly studied in the past but must be better understood before batteries are operated at high current rates using this manner of construction. The intent of the work being performed and documented here was to collect current data from parallel arrays of cells using a novel construction and diagnostic techniques. The study performed measured the current imbalance present in 1S/5P and 1S/30P arrays, respectively, under two different high-rate pulsed discharge profiles. The data has been analyzed to study any current imbalances that occur and the impact it has on battery performance and longevity. A novel testbed with independent cell diagnostics has been developed so that each cell has self-contained voltage, current and temperature measurements. Six unique test series were performed and those are discussed in detail here. This dissertation covers the methodology behind the research, the test bed, the results collected, and some implications learned from the analysis performed.

Keywords

LiFePO4, Battery Aging, Battery Characterization, Parallel Battery, Load Distribution

Disciplines

Electrical and Computer Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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