Owing to high oil prices and the efforts to reduce greenhouse gases according to the United Nations Framework Convention on Climate Change, there has been active research and development on environmentally friendly, high-efficiency vehicles. In developing the system design and specifications of an environmentally friendly vehicle, various simulations have been performed on the different components and the overall system. Although a precise modelling of each part and the system as a whole is necessary for an accurate simulation, detailed modelling of a high-capacity battery systemwhich directly affects the performance of an environmentally friendly vehicleis difficult to achieve owing to the non-linear electrochemical properties of the battery. In this study, an electrochemical impedance measurement technique is used to implement a battery cell model, upon which a battery system model for environmentally friendly vehicles that takes into account the ancillary components of the battery pack is developed. And we used an actual battery system that requires complex and difficult modelling owing to non-linear and irreversible properties of the battery. In addition, to verify the developed battery system model, we used models implemented for other vehicle components and systems to construct a hardware-in-the-loop simulation of a battery reflecting an actual driving environment.

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Online simulations are utilized to reduce time and cost in the development and performance optimization of plug-in hybrid electric vehicle (PHEV) and electric vehicles (EV) systems. One of the most important factors in an online simulation is the accuracy of the model. In particular, a model of a battery should accurately reflect the properties of an actual battery. However, precise dynamic modeling of high-capacity battery systems, which significantly affects the performance of a PHEV, is difficult because of its nonlinear electrochemical characteristics. In this study, a dynamic model of a high-capacity battery cell for a PHEV is developed through the extraction of the equivalent impedance parameters using electrochemical impedance spectroscopy (EIS). Based on the extracted parameters, a battery cell model is implemented using MATLAB/Simulink, and charging/discharging profiles are executed for comparative verification. Based on the obtained results, the model is optimized for a high-capacity battery cell for a PHEV. The simulation results show good agreement with the experimental results, thereby validating the developed model and verifying its accuracy.

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The ultracapacitor module has recently been recast for use in hybrid energy storage systems (HESSs). As a result, accurate state-of-charge (SOC) estimation for an ultracapacitor module is as important as that of primary sources in order to be utilized efficiently in an energy storage system (ESS). However, while SOC estimation via the open-circuit voltage (OCV) method is generally used due to its linear characteristics compared with other ESSs, this method results in many errors in cases of highcurrent charging/discharging within a short time period. Accordingly, this paper introduces a dynamic SOC estimation algorithm that is capable of SOC compensation of an ultracapacitor module even when there is a current input and output. A cycle profile that simulates the operating conditions of a mild-HEV was applied to a vehicle simulator to verify the effectiveness of the proposed algorithm.