Research Repot on A123 Battery Modeling

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Research Repot on A123 Battery Modeling

• Task 4 Members
• Faculty Dr. Mo-Yuen Chow, Dr. Srdjan Lukic
• Research Assistants Lei Wang, Arvind Govindaraj

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Presentation Outline

• Research Objectives
• Battery Properties
• Battery Model
• Future Research

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Research Objectives

• Battery Modeling
• Develop Charging Algorithms

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Presentation Outline

• Research Objectives
• Overview of battery properties
• Battery Model
• Future Research

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PHEV Battery Operation Modes

• Charge-depleting mode vehicle uses battery power
  until SOC reaches a predetermined level
• Charge-sustaining mode uses both battery and
  engine power
• Blended mode charge-depleting mode with engine
  power to reach high speed

Ex. 90 of time discharging, 10 charging
Ex. 30 discharging, 70 charging
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A123 Lithium Ion ANR26650M1
25C, C/30
lt 20A tested
SoH
ANR26650M1 Datasheet AUGUST 2008
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A123 Lithium Ion ANR26650M1
Not available

• Operating range -30c to 60c
• Performance under different temperatures was not
  tested
• Discharge curve shape changes at extreme
  temperatures, thus may not be described by model
  equations

• Maximum discharge 70A
• Model may fail at high discharge current due to
  irregular shape of the discharge curve

First Step Have a model that satisfies the
nominal condition
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Quantify Battery

• State of Charge (SoC) 100 gt SoC gt 0
• SoC (remaining capacity) / (capacity of fully
  charged battery)
• SoC (remaining capacity) / (Total amount of
  usable charge at a given C-rate)
• SoC (Cn Qb) / Cn
• Cn nominal capacity
• Qb net discharge
• Remaining Capacity ? Usable Capacity
• Usable capacity depends on the cutoff voltage
• Usable capacity depends on the age of the battery
  
• Capacity of fully charged battery ? Total amount
  of usable charge at a given C-rate ? Cn (C/30)

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Usable Capacity
Discharge Rate 1A 7738s x 1A / 3600s 2.149Ah
Discharge Rate 5A 1537s x 5A / 3600s 2.136Ah
T1537s
T7738s
Discharge Rate 10A 1389s x 10A / 3600s
2.1215Ah
Discharge Rate 20A 683s x 20A / 3600s 2.098Ah
T683s
T1389s
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Usable Capacity vs Discharge rate
Rated Capacity at 2.3Ah (using C/30 discharging
rate)
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Quantify State of Health (SoH)

• Full Discharge Test (SOH)
• SoH (measured capacity) /(rated capacity)
• 1 gt SoH gt 0 A battery is at its end of lifetime
  at SoH of 0.8 . (Energy Institute Battery
  Research Group)
• Increase in internal resistance resulting active
  power loss
• Increase in self discharge
• Counting charge/discharge cycles
• Voltage drop during initial discharge
• Two-Pulse Load Test

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State of Function (SoF)

• Capability of the battery to perform a specific
  duty which is relevant for the functionality of a
  system powered by the battery.
• For example Use 20A to discharge a battery
• after 683s battery reaches the cutoff voltage 2v
• Battery still has the capacity left to be
  discharged by 10A
• SoF is a function of the batterys SoC, SoH and
  operating temperature.

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Presentation Outline

• Research Objectives
• Battery Properties
• Battery Model
• Model results and analysis
• Future Research

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Discharging Results
1A
5A
10A
20A
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Discharging Results - Average
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Temperature vs Time
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Battery Model
Zk State of Charge ?i Cell Coulombic efficiency
(Eta 1 for discharge) Cn Cell nominal
capacity ?t sampling period Yk Cell Terminal
Voltage
Shepherd model yk E0 - Rik - Ki/zk Unnewehr
universal model yk E0 - Rik - Kizk Nernst
model yk E0 - Rik K2 ln(zk) K3 ln(1-zk)
Least Squared Fit Y KA AY
KAA Matlab k (inv(A'A))A'Y
Gregory L. Plett, University of Colorado at
Colorado Springs, Extended Kalman filtering for
battery management systems of LiPB-based HEV
battery packs Journal of Power Sources 134 (2004)
252261
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Constant Current Discharging _at_ 20A, 10A, 5A, 1A
Y observed data F model data
R2_01A 0.99R2_05A 0.97R2_10A 0.93R2_20A
0.85
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Voltage Error Actual voltage estimated
1A lt0.05V
5A lt0.07V
Error is very small Usually dont fully discharge
or charge the battery
10A lt0.07V
20A 0.3V
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Model 20 - 80 of SOC

• At a low state of charge nearly all the charging
  current is absorbed by the chemical reaction.
• Above 80 of SOC, more and more energy goes into
  heat.
• reduce current for the last 20

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Model output Smooth line
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Measured
Zoomed in
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Interval Discharge 5A for 60s 20A for 30s

• Purpose When driving, different discharging
  currents are applied to the battery

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Hysteresis

• Hysteresis slowly changes as the cell is charged
  or discharged
• Hysteresis is considerably larger at low
  temperatures.

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Modeling hysteresis effect

• constant ? tunes the rate of decay
• M is a function that gives the maximum
  polarization due to hysteresis as a function of
  SOC and the rate-of-change of SOC.

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Relaxation effect

• If a cell is pulsed with current, it takes time
  for the voltage to converge to its steady-state
  level.
• Relaxation effect may be implemented as a
  low-pass filter on ik
• The output equation had the form

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Simulink Model
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Result
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Future Work

• Pulse Discharging
• SoH, SoF
• Charging Algorithms
• Optimum power usage

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Acknowledgement

• Please use one of the following three languages
• This work was supported by ERC Program of the
  National Science Foundation under Award Number
  EEC-08212121.
• This work made use of ERC shared facilities
  supported by the National Science Foundation
  under Award Number EEC-08212121.
• This work was partially supported by the National
  Science Foundation (NSF) under Award Number
  EEC-08212121.