1. Using Battery Modeling as a Sizing Tool
IEEE ESSB Summer Meeting
Chicago – June 12, 2016

2. IEEE battery sizing Sizing standards Both use modified Hoxie method
IEEE Std for vented and valve-regulated lead-acid
IEEE Std for nickel-cadmium
Both use modified Hoxie method
Hoxie, E. A., “Some discharge characteristics of lead-acid batteries,” AIEE Transactions (Applications and Industry), vol. 73, no. 1, pp. 17–22, Mar
Divide duty cycle into successive periods with constant load
Size by section with progressively more periods
Section 1 with first period only
Section 2 with first two periods
Etc.
American Institute of Electric Engineers merged with Institute of Radio Engineers in 1963 to form IEEE
Using Battery Modeling as a Sizing Tool

3. IEEE cell sizing worksheet (IEEE 1115)
Using Battery Modeling as a Sizing Tool

4. Limitations for the IEEE method
Cumbersome for numerous load steps
No consideration for temperature changes during operation
Ambient changes during prolonged duty cycles
I2R heating effects
No consideration for ramping loads
No consideration (yet) for new technologies
Using Battery Modeling as a Sizing Tool

5. Battery modeling – an alternative approach
Various platforms depending on need. Examples:
COMSOL Multiphysics
‘Micro’ modeling e.g. electronic & ionic charge transfer
Useful for cell design
Matlab-Simulink
‘Macro’ modeling of electrical and thermal characteristics
Scalable to battery level for interactions with dc system
Models for advanced technologies may include battery- management algorithms
Using Battery Modeling as a Sizing Tool

6. Saft Li-ion Matlab-Simulink models
Models run same algorithms as battery management systems
Exactly mimic real battery behavior, including contactor management
Include aging inputs and outputs
Using Battery Modeling as a Sizing Tool

7. Example 1 – from IEEE 485
Model requires random load to be in correct location
Assume ambient temperature of 10 °C
Using Battery Modeling as a Sizing Tool

8. Example 1 – model results
BOL
100% SOH
EOL
80% SOH
Using Battery Modeling as a Sizing Tool

9. Example 2 – PJM regulation
PJM Interconnection runs the grid in 13 states
Biggest Independent System Operator in the USA
PJM power market includes fast regulation service (RegD) typically supplied by battery energy storage systems
Approx. 300 MW in service or being built
RegD signal is energy neutral and changes every 2 sec.
Sample day:
Using Battery Modeling as a Sizing Tool

10. Example 2 – model results
Using Battery Modeling as a Sizing Tool

11. So is modeling the future of battery sizing?
For Saft, the answer is ‘yes’
But not every battery manufacturer has a model
Most are less sophisticated
Tabular discharge data does not exist for Saft Li-ion cells
The model is the source of all performance characteristics
Using Battery Modeling as a Sizing Tool

12. Where do we go with sizing standards?
The IEEE sizing standards have their origins in the time before computer-driven modeling
Needed to avoid use of different sizing methods for the same project
Continue to be vital for the nuclear industry
Why do we need sizing standards if models exist?
Is validation an issue?
How is ‘trust the model’ different from ‘trust the tabular discharge data’?
Food for thought…
Using Battery Modeling as a Sizing Tool

13. Questions? Thoughts? jim.mcdowall@saftbatteries.com
Using Battery Modeling as a Sizing Tool

14. ‘Bonus’ material – cycle counting
Question
How many cycles?
…of what depth?
Answers are important for folks who want to compare cycle count with published cycle-life curves
The following slides show the Saft method
Others may follow a slightly different approach
Using Battery Modeling as a Sizing Tool

15. Cycle counting technique
Cycle must be ‘closed’
SOC must return to starting point
Example with 2 closed cycles
From 80% SOC to 20% SOC and back again (60% DOD)
From 55% SOC to 50% SOC and back again (5% DOD)
Using Battery Modeling as a Sizing Tool

16. Modified example Still 2 closed cycles
From 65% SOC to 20% SOC and back again (45% DOD)
From 55% SOC to 50% SOC and back again (5% DOD)
Cycle starting from 80% still waiting to be closed
If charging continued (after pause) up to 80% SOC...
45% cycle would become 60% DOD cycle
Using Battery Modeling as a Sizing Tool

17. Another modification Now 3 closed cycles
From 65% SOC to 20% SOC and back again (45% DOD)
From 55% SOC to 50% SOC and back again (5% DOD)
From 80% SOC to 30% SOC and back again (50% DOD)
With Li-ion we count only delta-DOD cycles
Cycle between 20% and 10% SOC counts same as one between 90% and 80% SOC
Hence no 60% DOD cycle above
Using Battery Modeling as a Sizing Tool