Download Application of the PNGV Lumped Parameter Battery Model

Chester G. Motloch, Jon Christophersen, Chinh D. Ho
Idaho National Engineering & Environmental Laboratory
Ira Bloom, Vince Battaglia, Argonne National Laboratory
Raymond A. Sutula, U.S. Department of Energy
Ted Miller, Ford Motor Company
Rdis
Ro + Rp
5
10
(Rreg + Rdis)/2
Rreg
Ro
Rp
0.045
0.04
0.035
Resistance (ohm)
Application of the PNGV Lumped
Parameter Battery Model
Jeffrey R. Belt, Senior Engineer
Idaho National Engineering and Environmental
Laboratory
PO Box 1625, Idaho Falls, ID 83415-3830
Phone: 208-526-3813
Fax:
208-529-0969
Email: [email protected]
0.03
0.025
0.02
0.015
0.01
0.005
0
0
15
20
25
30
Time (wk)
The PNGV Lumped Parameter Battery Model correlates
battery data to a simplified electrical circuit. The model
estimates parameters that are difficult or impossible to
determine from available test data. The estimated
parameters include open circuit battery voltage, internal
ohmic resistance, internal polarization resistance,
polarization time constant and capacitance. The Lumped
Parameter Model predicts ATD Gen 2 HPPC resistances
extremely well.
Fig. 1: Comparison of Lumped Parameter Model Ro
and Rp with HPPC Rdis and Rreg for an ATD Gen 2 Cell
at 45°C and 60% SOC.
35
Percent Change in Resistance (%)
The U.S. Department of Energy (DOE) initiated the
Advanced Technology Development (ATD) Program in
1998 to address barriers that limit the commercialization
of high-power lithium-ion batteries in hybrid electric
vehicle applications. As part of the ATD program,
standardized calendar- and cycle-life tests age 18650-size
cells at Idaho National Engineering and Envirionmental
Laboratory and Argonne National Laboratory. Every four
weeks, hybrid pulse power characterization tests (HPPC)
quantify capacity and power fade rates of these cells.
Rp
30
25
20
15
10
Rp
5
0
0
5
10
15
20
25
30
Time (w k)
Equally important is the time dependence of the ohmic
and polarization resistances estimated by the Lumped
Parameter Model. Fig. 2 shows the percent change in Ro
and Rp versus time. Figure 3 shows the linear fit for the
Rp data and a square-root of time fit for the Ro data for
the same cell. Figs. 2 and 3 are typical for cells tested at
45°C at INEEL. The time dependence of the ohmic
resistance is linear with the square root of time, which is
consistent with diffusion mechanisms. The polarization
resistance shows a simple linear time dependence.
The results of the Lumped Parameter Model agree with
the results from an independent HPPC test analysis.
Moreover, Rp increases linearly with time and Ro
increases with the square root of time.
References
1.
PNGV Battery Test Manual, Revision 3, DOE/ID10597, February 2001
Fig. 2: Percent change in Ro and Rp as a function of
time for an ATD Gen 2 cell at 45°C
35
Ro, sqrt(time)
Percent Change in Resistance(%)
An HPPC pulse consists of a discharge pulse (Rdis) and a
regen pulse (Rreg), from which resistances can be directly
calculated. The Lumped Parameter Model estimates the
overall ohmic (Ro) and polarization (Rp) resistances for
an HPPC pulse without differentiating between discharge
and regen pulses. The sum of Ro and Rp is essentially
equal to the average of Rdis and Rreg for ATD cells aged
at 45°C at 60% SOC at INEEL. See Figure 1.
30
y = 6.0782x + 0.1186
R 2 = 0.9988
25
20
15
Rp
10
y = 0.4749x - 0.4652
R 2 = 0.991
5
0
0
5
10
15
20
25
-5
sqrt (time) or time (wk)
Fig 3: Time dependencies of Ro and Rp for an ATD
Gen 2 cell at 45°C
30