Battery Management and Battery Modeling Considerations for Application in a Neighborhood Electric Vehicle

Abstract

Transitioning from internal combustion engine vehicles (ICEVs) to electric vehicles (EVs) consolidates and relocates emissions, endeavoring to improve air quality, particularly in high traffic urban areas. Unfortunately, many obstacles to widespread EV use remain, broadly related to user familiarity, convenience, and effectiveness. However, EVs are better suited for some opportunities. Following the introduction, this thesis covers the process of upgrading a neighborhood electric vehicle (NEV) from lead-acid batteries to a swappable battery pack consisting of lithium iron phosphate (LiFePO4), or LFP, cells. Although LFP cells are considered safer than other lithium-ion cells, a new battery charger and battery management system (BMS) were installed to ensure proper function and maintenance. While the new electronics appeared to be successfully integrated during initial testing, several cells within the battery pack were over-discharged—or underwent voltage reversal—while outside during winter. Thus, prompted a reassessment of battery management practices and implementation, resulting in the construction of a new battery pack and redesign of the charge and discharge controls. The ensuing chapter pertains to battery management practices employed in the vehicle—and battery management in general. This chapter begins with background, wherein discusses fundamentals of cell function, modes of failure, and lastly, methods of obviating failure and protracting cell longevity. Finally, chapter four describes battery modeling from the perspective of a tool to maintain cells in EVs. Determination of immeasurable states that are important to battery management and consumer comfort are deliberated. Mathematical models and equivalent circuit models of cell behavior are of particular interest. Common equivalent circuit models are parameterized for several cells and voltage estimation capabilities are compared.