Modeling of Lithium-Ion Battery for Energy Storage System Simulation

B. Charge Characteristics
In this part of the study, the Ultralife UBBL10 lithium-ion
battery was charged by a constant current 0.8A until the
battery voltage reached 16.33V. Then the charging mode
changed to constant voltage and the charge current eventually
decayed to zero. This charging procedure is common, as can
be seen in [9].
Fig. 7 shows the voltage increases during the charging
operation. When the voltage reaches the maximum value of
16.34 V, it remains at this value. That is reasonable for the
lithium-ion battery studied.
Fig. 7. Charging of the Ultralife UBBL10 lithium-ion battery:
comparison between simulation and test results
C. Thermal Characteristics
In this part, the model is used to study how heat sink can
affect battery operation. Using the same lithium-ion battery
model written in VHDL-AMS with the initial SOD of the
battery set to 0 and the load set to draw a constant current of 2
A, the heat transfer coefficient was varied.
Fig. 8 shows the simulation results of the battery
temperature during discharge under different cooling
conditions. Notice that the final temperatures are 28.2°C
(301.2°K) and 33.5°C (306.5°K) respectively for the constant
cooling coefficients of 5 W/m 2 K and 1 W/m 2 K. The battery
temperature is nearly equaled to the ambient (25°C) for very
large cooling coefficients (hc = 100 W/m 2 K). From the
simulation results, it can be concluded that the battery
temperature increases faster when the constant cooling
coefficient is lower.
Fig. 8. Simulation results of battery temperature during
discharge (2A, 25� ambient) for different cooling conditions
IV. CONCLUSIONS
A model of a lithium-ion battery suitable for energy storage
application has been shown. The model was formulated in a
general sense, but specifically for use in the SIMPLORER
software. The method accounts for current rate- and
temperature- dependence of the capacity and thermal
dependence of the equilibrium potential. The modeling
procedure, based on the experimental data, allows the model
to have both good accuracy and the flexibility to represent
other types of batteries. The mathematical description of the
battery has been coded to a VHDL-AMS model in the
SIMPLORER software.
The battery model is shown to perform satisfactorily, up to
the cutoff voltage. It is governed by the k th order term in the
polynomial representation of the reference curve. Simulation
results of the battery model agree well with the experimental
data of an Ultralife UBBL10 lithium-ion battery in all static
characteristics. This is because the internal resistance was
defined based on the experimental data. It has two components
R1 and R2. R1 is the initial resistance of the lithium-ion battery.
It depends on the different discharge condition of
temperatures, current levels and lifecycle. R2 is the increased
resistance with the SOD.
ACKNOWLEDGMENTS
The authors would like to thank the technical staff of the Power
Electronics and Drives Laboratory for the support given.
Special thanks to Mdm Lee-Loh for her technical support in the
equipment usage and software installation. Special thanks also
go to D.L.Yao and T.D. Nguyen.
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