State-of-Charge determination in imbalanced lithium-ion ... · State-of-Charge determination in...
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1680 East West Road, POST 109, Honolulu, HI 96822 Ph: (808) 956-2349 Fax: (808) 956-2336 State-of-Charge determination in imbalanced lithium-ion battery packs Matthieu Dubarry [email protected] Arnaud Devie, Patrice Cabanel & Bor Yann Liaw A01: Joint General Session: Batteries and Energy Storage -and- Fuel Cells, Electrolytes, and Energy Conversion Abstract #A01-0128, Battery System IV, Thursday October 15 2015
Transcript of State-of-Charge determination in imbalanced lithium-ion ... · State-of-Charge determination in...
1680 East West Road, POST 109, Honolulu, HI 96822
Ph: (808) 956-2349 Fax: (808) 956-2336
State-of-Charge determination in imbalanced lithium-ion battery packs
Matthieu Dubarry
Arnaud Devie, Patrice Cabanel & Bor Yann Liaw
A01: Joint General Session: Batteries and Energy Storage -and- Fuel Cells, Electrolytes, and Energy ConversionAbstract #A01-0128, Battery System IV, Thursday October 15 2015
SOC estimation is of extreme importance for the reliability and safety of battery operation in large scale energy storage systems.
How to estimate SOC for an assembly of cells in a battery pack remains a subject of great interest.
We recently proposed a new method for SOC determination and tracking for multi-cell assemblies from the single cell (SC) attributes.
In this work we’ll put this method in application for the study of a 3S1P string with temperature imbalance
Objectives & Motivations
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Single cells SOH SOC imbalance
Pack SOC and SOH
+Uses SC attributes Uses SC matching
Full SC/pack correlation:
Anakonu approach: Single cell/Pack correlation
packQr =( 𝑆𝐶𝑖𝑆𝑂𝐶(RCV1 − 𝑆𝐶𝑖𝑆𝑂𝐶(RCV2 SCiQr
𝑝𝑎𝑐𝑘𝑆𝑂𝐶(RCV1 − 𝑝𝑎𝑐𝑘𝑆𝑂𝐶(RCV2
=Q
∆packSOC
𝑂𝑃𝑉 𝑆𝐶1𝑆𝑂𝐶 = 𝑆𝐶1𝑂𝐶𝑉 𝑆𝐶1𝑆𝑂𝐶 + 𝑖=2
𝑛
𝑆𝐶𝑖𝑂𝐶𝑉 SCisf 𝑆𝐶1𝑆𝑂𝐶 + SCitf
SCitf = 𝑆𝐶1𝑆𝑂𝐶(RCV1 − 𝑆𝐶𝑖𝑆𝑂𝐶(RCV1SCisf = 𝑆𝐶𝑖𝑆𝑂𝐶(RCV1 − 𝑆𝐶𝑖𝑆𝑂𝐶(RCV2
𝑆𝐶1𝑆𝑂𝐶(RCV1 − 𝑆𝐶1𝑆𝑂𝐶(RCV2
With 2 sets of RCVs we can calculate the full OPV=f(packSOC) and packQr
RCV1 RCV2. . .
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
RCV: Rest Cell Voltage
Full SC/pack correlation:
OPV is a function of OCV of all single cells within assembly
Not directly proportional: need 2 adjustments for every single cell
A scaling factor sf (“SC capacities ratio”)
A translation factor tf (“SC SOC imbalance”)
Both calculable from RCV gathered information
Their evolution characterize pack imbalance.
Anakonu approach: Single cell/Pack correlation
𝑶𝑷𝑽 𝑆𝐶1𝑆𝑂𝐶 = 𝑆𝐶1𝑶𝑪𝑽 𝑆𝐶1𝑆𝑂𝐶 + 𝑖=2
𝑛
𝑆𝐶𝑖𝑶𝑪𝑽 SCisf 𝑆𝐶1𝑆𝑂𝐶 + SCitf
SCitf = 𝑆𝐶1𝑆𝑂𝐶(RCV1 − 𝑆𝐶𝑖𝑆𝑂𝐶(RCV1SCisf = 𝑆𝐶𝑖𝑆𝑂𝐶(RCV1 − 𝑆𝐶𝑖𝑆𝑂𝐶(RCV2
𝑆𝐶1𝑆𝑂𝐶(RCV1 − 𝑆𝐶1𝑆𝑂𝐶(RCV2
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Graphical analogy:
Align all the single cell OCV data
using the 2 RCVs points as anchors
Anakonu approach: SC/Pack correlation
Cells with different capacity ration
SC1SOC
Q
SC1RCV1
SC1RCV2
SC2SOC
SC3SOC
SC2RCV1
SC3RCV1
SC2RCV2
SC3RCV2
Cell #1
Cell #2
Cell #3
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Q
Q
All Qr and SOC mismatches can be accommodated with simple scalings and translations
Anakonu approach: SC/Pack correlation
Cells with different capacity ration
Pack
0
SC2SOC
SC3SOC
SC2RCV1
SC3RCV1
SC2RCV2
SC3RCV2
Cell #1
Cell #2
Cell #3
packSOC
RPV1RPV2
SC1SOC
Q
SC1RCV1
SC1RCV2
SC2sf
SC3sf
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Graphical analogy:
Align all the single cell OCV data
using the 2 RCVs points as anchors
Introducing scaling factor (sf)
and translation factor (tf)
SC2tf
SC2tf
Graphical analogy:
Cell degradation modifies the cells
Same RCV1 but different OCV and Qr
Anakonu approach: SC/Pack correlation
Cells with different SOH
2.8
3
3.2
3.4
3.6
3.8
4
4.2
0 20 40 60 80 100
0% LLI4% LLI8% LLI12% LLI16% LLI20% LLI
Vo
lta
ge
(V
)
SOC (%)
Cell #10% LLI
Cell #210% LLI
Cell #320% LLI
M. Dubarry, C. Truchot and B.Y. Liaw, J.Power Sources, 219 (2012) 204-216
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Graphical analogy:
Cell degradation modifies the cells
Same RCV1 but different OCV and Qr
Anakonu approach: SC/Pack correlation
Cells with different SOH
2.8
3
3.2
3.4
3.6
3.8
4
4.2
0 20 40 60 80 100
0% LLI4% LLI8% LLI12% LLI16% LLI20% LLI
Vo
lta
ge
(V
)
SOC (%)
SC1SOC
Q
SC1RCV1
SC1RCV2
SC2SOC
SC3SOC
SC2RCV1
SC3RCV1
SC2RCV2
SC3RCV2
Cell #10% LLI
Cell #210% LLI
Cell #320% LLI
M. Dubarry, C. Truchot and B.Y. Liaw, J.Power Sources, 219 (2012) 204-216
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Graphical analogy:
Cell degradation modifies the cells
Same RCV1 but different OCV and Qr
Anakonu approach: SC/Pack correlation
Cells with different SOH
2.8
3
3.2
3.4
3.6
3.8
4
4.2
0 20 40 60 80 100
0% LLI4% LLI8% LLI12% LLI16% LLI20% LLI
Vo
lta
ge
(V
)
SOC (%)
Pack
0
SC2SOC
SC3SOC
SC2RCV1
SC3RCV1
SC2RCV2
SC3RCV2
packSOC
RPV1RPV2
SC1SOC
Q
SC1RCV1
SC1RCV2
M. Dubarry, C. Truchot and B.Y. Liaw, J.Power Sources, 219 (2012) 204-216
Cell #10% LLI
Cell #210% LLI
Cell #320% LLI
All aging mismatches can be accommodated with an update of the SC
OCV curves and simple scaling and translation operations
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Experimental validation:
3S1P with temperature imbalance
25°C
60°C
25°C 60°C 25°C
Pack degrading much fasterDifferent SC degradation?Evolution of SOC imbalance?
2 cells cycling on their own at 25°C and 60°C
3 cells cycling in a stringwith 2 cells @ 25°C and1 cell @ 60°C
Cycling experiment:
Understand impact of temperature imbalance on cell assembly performance
Compare degradation of 3S1P assembly with single cells:
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200 250 300 350 400
25oC
60oC
Battery pack 25/60/25oC
Cap
acity (
Ah
)
Cycle number
Objective:
Use SC OCV curves &
String RCVs to calculate
Pack OPV curve
Experimental validation: 3S1P with temperature imbalance
OCV & RCV evolution
25°C
60°C
25°C 60°C 25°C
Experimental OCV vs. SOC relationships
+
10.8
11.4
12
12.6
3.6
3.8
4
4.2
0 50 100 150 200 250 300 350
Pack
Cell 1 (25oC)
Cell 2 (60oC)
Cell 3 (25oC)
Ba
tte
ry p
ack v
oltag
e (
V) S
ingle
cells
vo
ltag
e (V
)
Cycle number
Use SC OCVs and string RCVsto calculate pack OPV
Vs.
Initial cycle 250th cycle
Experimental validation: 3S1P with temperature imbalance
OPV Simulation
Overall good estimation
Experimental validation: 3S1P with temperature imbalance
OPV calculations
Experimental data
Simulations
Average calculation error ranges from0.7% initially to 3% after 300 cycles.Maximum error 5.5%
Errors if using the initial OPV asreference ramps up to close to 12% withan average at 8%.
25°C cell: sf stable but SOC scales shifted by ~5%
60°C cell: lost 30% more capacity and its SOC scale shifted by ~40%
Experimental validation: 3S1P with temperature imbalance
tf and sf variations
Degradation ratio 25°C/60°C slightly larger than that of single cells (0.8)
Degradation of the cells is comparable insingle cell and string testing.Accelerated capacity loss for the string isinduced by drifting of tf.
0.5
0.6
0.7
0.8
0.9
1
0 50 100 150 200 250 300
sf va
ria
tion
(%
)
Cycle number
sf Ref: 25°C
60°C
25°C
Ref:
-10
0
10
20
30
40
0 50 100 150 200 250 300
tf v
aria
tion (
%)
Cycle number
tf
25°C
60°C
25°C
0.2
0.4
0.6
0.8
1
1.2
0 50 100 150 200 250 300 350 400
25oC
60oC
Battery pack 25/60/25oC
Cap
acity (
Ah
)
Cycle number
Unique and simple packSOC estimation method
No physical disassembly, no pack maintenance: reduced downtime
Requires only two measurements of rest cell voltages of all single cells
Reduce the complexity in the SOC & SOH tracking:
Significant benefits to battery control and management
Two parameters, tf and sf to characterize and track cell imbalance
Enables RUL determination with improved accuracy.
Can be coupled with ‘alawa approach for degradation simulation
‘alawa: mechanistic approach towards battery diagnostics
Pack-level and cell-level degradation factors could be singled out and accurately quantified without complicated protocols and procedures.
Model paper:
Anakonu approach - Conclusions
M. Dubarry, C. Truchot, A. Devie and B.Y. Liaw, J. Electrochem. Soc. 162(6), p. A877 (2015).
Apply the technique on BESS scale battery packs
HNEI is monitoring several MW scale battery systems in Hawai’i
Topology of Big Island 1MW system: 384 modules in series (1S7P)
About 1 unscheduled downtime / month
1 reference test every 4 months
Should have enough data to apply this approach.
Future work
Acknowledgments
Cyril Truchot
FundingIdaho National Laboratory
US DOE EERE ABR
(Contract No. DE-AC07-05ID14517).
Thank you for your attention!
Questions ?
Full publication list available on and
http://www.soest.hawaii.edu/HNEI/alawa/
