Transcript Document
Double Layer Capacitors: Automotive Applications and Modeling
David A. New
John G. Kassakian
Joel E. Shindall
David J. Perreault
Massachusetts Institute of Technology, Laboratory for Electromagnetic and Electronic Systems
Validation of DLC Model
DLC Use in Automobiles
Abstract
•Charge the DLC with a constant current
•Discharge DLC through a resistive load
•Charge/discharge, charge/hold/discharge
capability
•Supplement to Battery
─ Ease of starting
─ Reduction of weight and volume of the current “oversized” battery
─ Increase lifetime of automotive battery
Prevention of frequent battery SOC dips that will decrease the lifetime of the battery
•Supply/accept high peak power demands efficiently
Computer:
LabView
─ Regenerative braking
Captured energy generated by the braking system
─ Brake-by-wire
─ Steer-by-wire
─ Integrated starter/generator
100A No Delay
4
74.67
74.70
Cycles
Lab (%)
PSpice (%)
Modeling of DLCs
HP 6011A
Current Source
TDS 754D
Voltage Meter
•Various experimental/simulation profiles
conducted
–100A No Delay, 100A Delay
–10A No Delay, 10A Delay
AM 503
Current
Amplifier
P6139A
V-Probe
ADA 400A
Differential
PreAmplifier
100A With Delay
3
74.72
72.67
10A No Delay
3
93.52
90.82
Discharge
Resistance
A6303
I-Probe
NESSCAP 2500F
P6139A
V-Probe
10A With Delay
1
77.41
76.59
100A Charging No Transistion Delay
0.5
0.4
Voltage [V]
This research project has concentrated on the modeling of double layer capacitors
(DLCs) and the validation of those models. Several experiments have been conducted to
subject the device under test to a variety of charging/discharging profiles in an effort to
extract model parameters from the device’s performance and to simulate the various
conditions such a device might encounter in an automotive type application. High and
low current charging profiles were performed for both charge/discharge and
charge/hold/discharge type experiments. The derived DLC model was then used in
PSpice® simulations to determine how accurately the model could predict the
performance of the device. This poster gives a look into the modeling of DLCs, the
experimental setup and testing procedure used to test the devices, the simulations for the
comparison, and presents the results of the comparison.
As a result, this poster
documents the conclusion that this simple model very adequately predicts the
performance of the device under these various performance profiles. Finally, the lowtemperature trends of these devices are illustrated by experimental results.
0.3
0.2
0.1
0
•“Short-term” Model: Fast, Medium, and
Slow Branches
•Device quickly charged to ~0.5V, voltage
decay due to charge diffusion
•Model parameters extracted from observed
behavior
•Very high capacitance per unit
volume and weight
•Low voltage devices (~3V)
•Superior charging/ discharging
efficiency
•Cycleability of device exceeds the
lifetime of most applications
Conventional
Capacitor
Note: Does not investigate
non-linear capacitance
Supercapacitors
(carbon based)
Rf
300
350
400
450
500
0
50
100
150
200
250
300
350
400
450
500
0
50
100
150
200
250
Time [s]
300
350
400
450
500
Current [A]
Power [W]
40
30
20
10
0
0.3
0.25
0.2
0.15
Rs
Cs
-10
0.1
0.05
0
500
1000
1500
2000
2500
Low-Temperature Trends
3000
Time [s]
Case
•First experiment determines 6 of the 7 model parameters
•Leakage resistance is not a dominant term when dealing with “short-term” time
periods (i.e. a few hours)
•Leakage resistance important for long-term behavior of device (i.e. 30 day “airport
test”)
•Second experiment to determine leakage resistance
macropore
(>500Å)
•Investigate the effects of low-temperature on DLC
model parameters
•Constructed low-temperature setup that utilizes a
liquid nitrogen coolant
•Device held at low-temperature for ~3hrs
•Experiment performed at ~-30ºC
Plexiglas
NessCap
2500F
Electrolyte
DLC
micropore
(20-8Å)
Average Ionic
Center
sub-micropore
(<8Å)
mesopore
(500-20Å)
Activated Carbon
Solid/Liquid Interface
Single Time Constant
Capacitor Model
•“Base-line” room-temperature
model determined
•Device charged to and held at 1V for extended period of time
•Minimize voltage decay due to ionic diffusion
•Periodic measurements of voltage decay
V ≅ 0.77V @ t ≅ 30 days
Actual DLC
Behavior
Heat sink
0.44m
Voltage
Decay
2700F
0.57
220F
Styrofoam
2.9
490F
Potentiostatic
Charge
•Model fitted to low-temperature
data
v(t)
Voltage Decay
Leakage Resistance
1V
1
Cm
250
50
0.35
0
1.1
Cf
200
60
0.4
Battery
Electrode Bulk
Rs
150
50
0.45
Electrodes
ion
Rm
Cm
100
0
Separator
Helmholtz Layer (few Angstroms)
•DLC are complex devices that are
modeled by multi-time constant
networks
Rm
NESSCAP 2500F, 100A Pulse
0.5
Rlk
Cf
C A/d
•Small charge separation
•High surface area
(1500-2400 m2/g)
Rf
50
100
Voltage [V]
What is a Double Layer Capacitor?
0
Cs
0.45m
2700F
1.7
140F
20
300F
Voltage [V]
0.9
0.8
0.7
3k
0.6
0.5
0.4
0
20
40
60
80
Time [days]
100
120
~1 Week
t
Model
Rf
Rm
Rs
Cf
Cm
Cs
Room-temperature
model
0.44m
0.57m
2.9
2700F
220F
490F
Low-temperature
model
0.45m
1.7m
20
2700F
140F
300F
140
Advantages of Double Layer Capacitors
•Carbon/carbon DLCs can be fully discharged without reducing the lifetime of the device
•Cycleability of DLC exceeds lifetime of automobile
0.68m
•Superior charging/discharging efficiency
•Higher specific power rating than Pb-acid battery
•Higher specific energy rating than conventional capacitor technologies
2.9
3k
2600F
•Minimal (if any) maintenance
0.8
250F
560F
Model: NessCap 2500F, 2.3V
•Derived model fits well to experimental data
Acknowledgements
•MIT/Industry Consortium on Advanced Automotive Electrical/Electronic Components and Systems for its
funding of this project.
•Ness Capacitor Co., Ltd (NCC), Maxwell Technologies, and Panasonic for supplying our devices.
•Thomas Keim, John Miller (J-N-J Miller Design), and Steven Leeb for their technical support and
guidance.
•Ivan Celanovic, Woo Sok Chang, Tushar Parlikar, Joshua Phinney, Juan Rivas, John Rodriguez, Wayne
Ryan, Sai Chun Tang, and David Wentzloff for their help in the lab and all the late night coffee.
MIT/Industry Consortium on Advanced Automotive Electrical/Electronic Components and Systems