Abstract

In order to meet the stringent cost targets for electric, hybrid electric, and plug-in hybrid electric vehicles (EVs, HEVs and PHEVs), a serious improvement in battery cycle-life and safety is undoubtedly essential. More recently, lithium batteries, in the form of lithium-ion, lithium-polymer or lithium iron phosphate have been profoundly explored. Despite critical research initiatives, lithium-based batteries have not yet been able to meet the steep energy demands, long lifetime and low cost, unique to vehicular propulsion applications. One of the most practical techniques of improving overall performance is to use suitable power electronics intensive cell voltage equalizers in conjunction with on-board energy storage devices. There have been some interesting developments in this area during the last few years, but cost constraints and high current specifications have prevented the complete deployment of this versatile technology. The purpose of this thesis is to introduce a novel configuration for a cell voltage equalizer, with the potential of fulfilling the expectations of low cost, high current-capability, and high efficiency. This thesis consists of six parts: the first part deals with an introduction to the battery problems in electric vehicle applications; the second part deals with a review of the available popular cell equalizer configurations; the third part deals with an economic and feasibility analyses of battery cell equalizers. Thereafter, a detailed analysis of the proposed novel battery cell equalizer configuration is presented, comparing the theoretical models, modeling and simulation results, and prototype measurements. A separate chapter is discusses from the point of view of power electronic converter control, considering practical issues. Finally, the thesis discusses the major motivating inferences drawn from this work, and suggests possible future directions and trends, based on those conclusions.