I. INTRODUCTION
The near-future technologies related to hybrid electric vehicles
(HEV) are the most promising alternatives to cope
with the reduction of greenhouse gases in the car industry. In
particular, plug-in HEV and vehicle-to-grid (V2G) concepts
will have a tremendous impact not only on the reduction of
greenhouse gases but also on electricity distribution systems.
Above all, these new technologies will heavily depend on
battery packs. It is therefore important to develop accurate
battery models that can conveniently be used with simulators
of power systems and on-board power electronic systems.
There are basically three types of battery models reported
in the literature, specifically: experimental, electrochemical
and electric circuit-based. Experimental and electrochemical
models are not well suited to represent cell dynamics for
the purpose of state-of-charge (SOC) estimations of battery
packs. However, electric circuit-based models can be useful
to represent electrical characteristics of batteries. The most
simple electric model consists of an ideal voltage source in
series with an internal resistance [1]. This model, however,
does not take into account the battery SOC. An other model
is based on an open circuit voltage in series with resistance
and parallel RC circuits with the so-called Warburg impedance
[2]. The identification of all the parameters of this model is
based on a rather complicated technique called impedance
spectroscopy [3]. Shepherd developed an equation to describe
the electrochemical behaviour of a battery directly in terms of
terminal voltage, open circuit voltage, internal resistance, discharge
current and state-of-charge [4], and this model is
applied for discharge as well as for charge. The Shepherd
model is interesting but causes an algebraic loop problem in
the closed-loop simulation of modular models. Battery models
with only SOC as a state variable are discussed in [5] [6].
These models are very similar to Shepherd’s but don’t produce
an algebraic loop.
In this paper, a model using only SOC as a state variable is
chosen in order to accurately reproduce the manufacturer’s
curves for the four major types of battery chemistries. These
four types are: Lead-Acid, Lithium-Ion (Li-Ion), Nickel-Cadmium
(NiCd) and Nickel-Metal-Hydride (NiMH). The paper
is divided into three sections. In the first section, the proposed
model and its parameters are described. Furthermore, a method
is presented to show how to determine the model parameters
from the manufacturer’s discharge curves of the battery. In the
second section, discharge curves are obtained by simulation
and validated with the manufacturer’s datasheets. The third
section contains an example of an application where the battery
model integrated to the SimPowerSystems (SPS) is used in the
complete simulation of an HEV power train. The paper ends
with a conclusion.