Characterization and Modeling of a Hybrid-Electric-Vehicle Lithium-Ion Battery Pack at Low Temperatures

Although lithium-ion batteries have penetrated hybrid electric vehicles (HEVs) and pure electric vehicles (EVs), they suffer from significant power capability losses and reduced energy at low temperatures. To evaluate those losses and to make an efficient design, good models are required for system simulation. Subzero battery operation involves nonclassical thermal behavior. Consequently, simple electrical models are not sufficient to predict bad performance or damage to systems involving batteries at subzero temperatures. This paper presents the development of an electrical and thermal model of an HEV lithium-ion battery pack. This model has been developed with MATLAB/Simulink to investigate the output characteristics of lithium-ion batteries over the selected operating range of currents and battery capacities. In addition, a thermal modeling method has been developed for this model so that it can predict the battery core and crust temperature by including the effect of internal resistance. First, various discharge tests on one cell are carried out, and then, cell's parameters and thermal characteristics are obtained. The single-cell model proposed is shown to be accurate by analyzing the simulation data and test results. Next, real working conditions tests are performed, and simulation calculations on one cell are presented. In the end, the simulation results of a battery pack under HEV driving cycle conditions show that the characteristics of the proposed model allow a good comparison with data from an actual lithium-ion battery pack used in an HEV.

I. Introduction

In recent years, hybrid electric vehicle (HEV) and electric vehicle (EV) technologies are considered to be the most promising solutions to cope with environmental and energy problems caused by the automotive industry. In particular, plug-in HEV and vehicle-to-grid concepts have assumed a prominent role in both industry and academic research due to their potential impacts on the reduction of greenhouse gases and electricity distribution systems. A key element to the success of this system is the battery technology. Among the major candidates for EV/HEV batteries, the specific energy and energy density of lithium-ion batteries have made them the first choice for EVs and HEVs. Although they have been broadly established in automotive products, the HEV/EV market is limited by technical barriers such as their safety [1], [2], cost issues [3], and recycling issues [4]. Above all, one other issue remains significant: the batteries' reduced energy and power densities at low temperatures [5].