Significance of Battery Cell Equalization and Monitoring for Practical Commercialization of Plug-In Hybrid Electric Vehicles

In order to increment gas mileage and meet CO₂ emission targets, automakers have recently started making serious advances towards all-electric and plug-in hybrid electric vehicles (PHEV). Since the last decade, the main obstacle has remained the same: energy storage. In recent years, lithium batteries have been vastly explored, but have not yet met the energy requirements for PHEVs. The main issues are: cost, cycle life, calendar life, energy density, power density, and more recently, safety. These grave issues can be easily addressed using an extremely practical approach: a suitable battery cell voltage equalizer. The main aim of this paper is to demonstrate the role of an appropriate cell equalizer to reach the cost breakpoint of a PHEV. Lithium rechargeable cells have been studied thoughtfully, but they do not include the cost benefit analysis of using advanced electronics to protect and equalize the cells. The paper will also introduce lithium battery degradation effects, in order to demonstrate the practicality of battery cell voltage equalizers. Thereafter, the paper presents an economic comparison between a typical cell equalizer topology and the proposed topology. Finally, the economical feasibility of a power electronics intensive equalizer-managed PHEV storage system will be proven.