Electrical energy storage, rather than fuel combustion, has become a key component in transit fleets that are switching to more efficient hybrid and electric vehicles. To help engineers and technicians make that change, researchers at Penn State’s Thomas D. Larson Pennsylvania Transportation Institute, funded through a grant from the Mineta National Transit Research Consortium, studied lithium titanate oxide battery chemistry for use in transit buses. The principal investigator was Timothy Cleary, MS, assisted by research associates Harshad Kunte, MS, and Jim Kreibick. The report can be viewed at http://transweb.sjsu.edu/project/1150.html
This research supports the work of those who are involved with battery system integration and management. The tools produced from the study are intended to help automotive engineers achieve optimal system performance and ultimately a more efficient vehicle.
The research team found, other than proprietary data/models, there was little technical information or research on electrical and thermal modeling of this advanced chemistry. So they developed a laboratory test setup of a prototype lithium titanate oxide battery pack to study their characteristic behaviors. They then produced state-of-charge estimators capable of running on the limited embedded processing power and memory of a typical battery management system.
“We also investigated the thermal performance of this chemistry in the large format, producing a physics-based empirical thermal model for use in system-level simulations,” said Cleary. “This model predicts pack-level thermal behavior by reporting the minimum, maximum, and average temperatures within a system typically used for large automotive applications, as testing was concentrated on transit bus usage profiles.”
Chapters in the 91-page report include: Introduction; Test Setup; Battery Management System SOC Estimation; Battery Management System Sensitivity Analysis; Equivalent Circuit Model; State-of-Charge Estimation Using Extended Kalman Filter; Thermal Testing; and Thermal Model. The publication includes 69 figures and two appendices.
