Design, Testing, and Validation of a Simplified Control Scheme for a Novel Plug-In Hybrid Electric Vehicle Battery Cell Equalizer

In order to meet cost targets for hybrid electric (HEV), plug-in hybrid electric (PHEV), and all-electric vehicles (EV), an improvement in the battery life cycle and safety is essential. Recently, lithium batteries, in the form of lithium-ion, lithium-polymer, or lithium iron phosphate have been explored. Despite research initiatives, lithium-based batteries have not yet been able to meet steep energy demands, long lifetime, and low cost of vehicular propulsion applications. One practical approach to improve performance is to use power electronics intensive cell voltage equalizers, in conjunction with on-board energy storage devices. The purpose of this paper is to introduce a simplified control scheme, based on open-circuit voltage estimation, for a novel cell equalizer configuration, with the potential to fulfil expectations of the following: 1) low cost; 2) large currents; and 3) high efficiency. Issues, such as the limitations on maximum and minimum cell voltage, noise, and quantization errors, are explored. Finally, a comprehensive comparison between the theoretical test results and practical equalization test results is presented.