Benefits of Battery-U Itracapacitor Hybrid Energy Storage Systems Ian C. Smith LOR17,AI iS

219 Pages·2012·8.37 MB·English

Benefits of Battery-U Itracapacitor Hybrid Energy
Storage Systems
by
Ian C. Smith
B.S., Electrical Engineering
Northeastern University, 2009
Submitted to the Department of Electrical Engineering and Computer
Science on May 17, 2012, in partial fulfillment of the requirements for
the degree of ARCHIVES
Master of Science in Electrical Engineering MASSACHUSETTS INSTITUTE
OF TE CNLOG7Y
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY JUL R
LOR1I7 ,AiS
June 2012
© Massachusetts Institute of Technology, 2012. All rights reserved.
Author
Department of Electrical Engineering and Computer Science
May 17, 2012
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Certified by
Thesis Supervisor: John G. Kassakian
Professor of Electrical Engineering and Computer Science
Accepted by
Leslie A. Kolodziejski
Chair, Department Committee on Graduate Students

Benefits of Battery-Ultracapacitor Hybrid Energy
Storage Systems
by
Ian C. Smith
Submitted to the Department of Electrical Engineering and Computer
Science on May 17, 2012, in partial fulfillment of the requirements for
the degree of
Master of Science in Electrical Engineering
Abstract
This thesis explores the benefits of battery and battery-ultracapacitor
hybrid energy storage systems (ESSs) in pulsed-load applications. It
investigates and quantifies the benefits of the hybrid ESS over its
battery-only counterparts. The metric for quantifying the benefits is
charge efficiency - the amount of energy delivered to the load per unit
charge supplied by the battery. The efficiency gain is defined as the
difference in charge efficiency between the hybrid and the battery-only
ESS.
A custom experimental apparatus is designed and built to supply the
current control for charging and discharging the batteries, as well as
the data acquisition for measuring energy and current output.
Experiments are performed on both ESSs under four different pulsed
load profiles:
1. 436 ms pulse period, 10% duty cycle, 8 A pulse amplitude
2. 436 ms pulse period, 25% duty cycle, 8 A pulse amplitude
3. 436 ms pulse period, 10% duty cycle, 16 A pulse amplitude
4. 436 ms pulse period, 25% duty cycle, 16 A pulse amplitude
Circuit models are created to accurately represent the battery and
ultracapacitors. These models are used in simulations of the same test
cases from the physical experiments, and efficiency gains are
compared. The circuit models differed from the experimentation by
less than 1%.
Both experimental and simulated data demonstrate significantly
increased charge efficiencies of hybrid ESSs over battery-only ESSs,
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with demonstrated gains between 10% and 36%. These benefits were
greatest for the 16 A, 10% duty cycle test case because it combined
the highest pulse amplitude and the shortest duty cycle. It is
concluded that high-amplitude, low duty cycle, and low period pulsed-
load profiles yield the highest efficiency gains.
Thesis Supervisor:
John G. Kassakian
Professor of Electrical Engineering and Computer Science
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Acknowledgements
I have many people to thank for making my time at MIT an amazingly
rich and rewarding experience.
I would like to first thank my thesis advisor - Professor John Kassakian
- for his immense amount of knowledge, wisdom, and patience.
Having access to such an outstanding and distinguished MIT professor
has been an amazingly educational experience, and has undoubtedly
bolstered my growth as an engineer and as a person. I must also
extend thanks to Professor Joel Schindall for mentoring me throughout
the project. His cool-headed voice of reason and industry experience
has pulled me back onto the right path too many times to count.
I would also like to thank the other members of the LEES community.
It takes a lab to raise an engineer and I feel incredibly fortunate to
have had 2 years in LEES. A special thanks, in particular, is due to the
following people for always being there to help me in a time of need
and to keep the mood light when it was getting too dark: Sam, Justin,
Richard, Andy, Minjie, Jackie, Wardah, and Juan. Thank you, Dave
Otten, for being a levelheaded voice of reason during all of the chaos.
And thank you to everybody else in 10-061 and 10-050 for some
memorable moments and good times.
To my parents, I cannot thank you enough for always supporting me.
Your advice and love have always kept me on the right course and I
am proud to say that I am your son. May this thesis serve as a
dedication to the values that I learned from both of you. Thank you
Gordon and Alan for being wonderful brothers and always, always
having a joke ready to keep the laughter flowing.
And finally, I would like to thank Dan, Brian, Jose, Matt, Tony, and
everybody else at Nest for giving me the opportunity to return for my
degree and for creating a wonderful place to call home after its
completion. I could not be more excited for the future and what it
brings - the sky is the limit!
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Contents
1
- INT RODUCTION............................................................................ 11
1.1 GENERAL CHARACTERISTICS OF ULTRACAPACITORS......................... 12
1.2 A BRIEF HISTORY OF ULTRACAPACITORS......................................... 16
1.3 PRIOR RESEARCH AND APPLICATIONS .............................................. 17
1.4 THESIS OVERVIEW ...................................................................... 20
2 - EXPERIM ENTATION ............................................................... 23
2.1 HARDWARE DESIGN .................................................................. 26
2.2 CALIBRATION AND DATA PROCESSING.......................................... 35
2.3 ANALYSIS AND RESULTS ............................................................. 44
2.4 CONCLUSION .......................................................................... 49
3 - SIMU LA TION.......................................................................... 51
3.1 ULTRACAPACITOR CIRCUIT MODEL ............................................. 52
3.2 BATTERY CIRCUIT MODEL ........................................................... 58
3.3 HYBRID ESS CIRCUIT MODEL ...................................................... 65
3.4 SIMULATION PROCEDURE ........................................................... 67
3.5 SIMULATION RESULTS................................................................. 69
3.5 CONCLUSION .......................................................................... 78
4 - CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK..... 79
4.1 CONCLUSIONS ......................................................................... 79
4.2 SUGGESTIONS FOR FUTURE W ORK .............................................. 81
BIBLIOGRAPHY............................................................................. 85
APPENDIX A ................................................................................... 89
APPENDIX B................................................................................ 123
APPENDIX C................................................................................. 163
APPENDIX D............................................................................... 171
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List of Figures
Figure 1. Ultracapacitor structure [6].......................................................... 14
Figure 2. The ultracapacitor and NiMH battery cell used in the ESS ....24
Figure 3. Test rig block diagram ................................................................... 27
Figure 4. High-current circuitry and control. Discharge circuitry is
highlighted in blue, charge in orange, and the energy storage
system is highlighted in green................................................................. 29
Figure 5. ADC m easurement nodes............................................................. 31
Figure 6. Op amp scaling circuits and their scaling constants...........31
Figure 7. Battery voltage and temperature during a constant-current
charge. The vertical line denotes the time at which charging
c e as e d ..................................................................................................................... 33
Figure 8. The test rig PCB layout. The red traces are on the top layer,
the large blue planes are the inner ground layer, and the small
blue traces are on the bottom layer. The inner power layer is
h id d e n ..................................................................................................................... 34
Figure 9. Example calibration of pulse-high and pulse-low scenarios
for an 8 A, 25% duty cycle pulse. The blue data points represent
the test rig sampling points. The green line is data from the
o scillo sco pe .................................................................................................... . . 38
Figure 10. Data output stream structure ................................................... 40
Figure 11. Plot of the sampling times, overlaid on top of a current
p u ls e ........................................................................................................................ 42
Figure 12. A single ultracapacitor circuit model......................................53
Figure 13. Comparing the original ultracapacitor model to experiment
during a long-term charge test................................................................ 55
Figure 14. Comparing the original ultracapacitor model with calculated
values to the experimental discharge pulses ..................................... 56
Figure 15. Comparing the four-branch ultracapacitor model simulation
to experimental data in a 10A pulsed discharge test......................58
Figure 16. Initial Panasonic Nickel-metal Hydride Battery circuit model
................................................................................................................................... 59
AV
Figure 17. Calculating battery ESR. rESR ~~ ......................................... 60
AI
Figure 18. Battery setting voltage to find the transient branch
re sista nce s ....................................................................................................... . 60
Figure 19. Comparing the two-branch battery model to experimental
d a ta .......................................................................................................................... 62
Figure 20. Final battery model, consisting of three RC branches.........63
8
Figure 21. Comparing the three-branch battery model to experimental
d a ta ............................................................................................................. . . . 64
Figure 22. Hybrid ESS model with 1 battery pack in parallel with 3
ultracapacitors in series......................................................65
Figure 23. Comparing the hybrid ESS model to experimental data.
Load voltage is on top, battery current on bottom. ........................ 66
Figure 24. Numerical Simulation Flowchart for a given time, t.........68
Figure 25. Optimizing the pulse variables for efficiency gain. Figure
25a) Pulse duty cycle; Figure 25b) amplitude; Figure 25c) period.
74
................................................................................... 7
Figure 26. Efficiency gains for low and high pulse periods.............76
Figure 27. Hybrid circuit model that was analyzed for the simulation
s c ript s .................................................................................................................... 164
Figure 28. Hybrid circuit model during a discrete time step.
Capacitors are represented as voltage sources....................................165
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List of Tables
Table 1. Ultracapacitor and battery component specs [31]. [32].........24
Table 2. Example unaltered readings from a 16 A 25% duty cycle
current pulse, with the data comma-separated in Microsoft Excel.41
Table 3. 16 A 25% duty cycle pulse variable multipliers. The 6 rows
represent a different sample during a 25% duty cycle pulse...........42
Table 4. Same stream of data from Table 2 after multiplying by the
multipliers from Table 3. The values are displayed in volts.....43
Table 5. Experimental data results for the short tests.......................... 45
Table 6. 16 A, 10% duty cycle tests, comparing 'short' test results to
the depletion test results (note the difference in units of energy
an d cha rg e )................................................................................................... . . 47
Table 7. Original three-branch ultracapacitor model component
values, based upon the procedure in [34].........................................54
Table 8. The final component values used for the four-branch
ultracapacitor m odel in Figure 12........................................................... 57
Table 9. Component values for the two-branch battery model........62
Table 10. Battery model component values..............................................64
Table 11. Simulation results for the same test cases that were run in
the experim ental chapter.......................................................................... 70
Table 12. Comparing simulated to experimental data outputs ........ 72
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