Feasibility Analysis of a Novel Cell Equalizer Topology for Plug-In Hybrid Electric Vehicle Energy-Storage Systems

To meet the stringent cost targets for hybrid electric, plug-in hybrid electric (PHEV), and all-electric vehicles, 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 profoundly been explored. Despite critical research initiatives, lithium-based batteries have not yet been able to meet the steep energy demands, long lifetime, and low cost, which are 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 onboard 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 paper 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. A comprehensive comparison between the theoretical novel equalizer, a typical equalizer, and the experimental prototype of the novel equalizer will be presented, which will help analyze performance, complexity, and cost.