Analysis of Ultracapacitor-VR

Storage Systems for Mild H

Tony Markel, Ahmad Pesaran, and Sam 

ahmad_pesaran@nrel.gov

5th Advanced Automotive Battery Confere

Honolulu, Hawaii

June 13-17, 2005

NREL/PR-540-41038
2 5th Advanced Automotive Battery Conference

Disclaimer and Government Lic

• This work has been authored by Midwest Research Institute (MRI) u

AC36-99GO10337 with the U.S. Department of Energy (the “DOE”Government (the “Government”) retains and the publisher, by acceppublication, acknowledges that the Government retains a non-excluworldwide license to publish or reproduce the published form of this 

do so, for Government purposes.

• Neither MRI, the DOE, the Government, nor any other agency there

employees, makes any warranty, express or implied, or assumes an

for the accuracy, completeness, or usefulness of any information, aprocess disclosed, or represents that its use would not infringe any 

Reference herein to any specific commercial product, process, or se

trademark, manufacturer, or otherwise does not constitute or imply recommendation, or favoring by the Government or any agency theopinions of the authors and/or presenters expressed herein do not n

those of MRI, the DOE, the Government, or any agency thereof. 
3 5th Advanced Automotive Battery Conference

Content 

• Background• Motivation/Objectives 

• Assumptions• Analysis Approach

• Results• Summary
4 5th Advanced Automotive Battery Conference

Background

• FreedomCAR’s Goals for mild hybrids a

for batteries. Could ultracapacitors play 
5 5th Advanced Automotive Battery Conference

Background (cont.)

• FreedomCAR’s gaols for ultracapacitors 

aggressive. Could VRLAs play a role? 

Selling Price ($/system @ 100k/yr) 40 80 

Maximum System Volume (Liters) 4 8 Maximum System Weight (kg) 5 10 

Survival Temperature Range (°C) -46 to +66 -46 to +66 Operating Temperature Range (°C) -30 to +52 -30 to +52 

Minimum Operating Voltage (Vdc) 9 27 

Maximum Operating Voltage (Vdc) 17 48 

Self Discharge (72hr from Max. V) <4% <4% 

Energy Efficiency on UC10 Load Profile (%) 95 95% Calendar Life (Yrs) 15 15 

Cycle Life and Efficiency Load Profile UC10 UC10 

Cycle Life / Equiv. Road Miles 750k / 150,000 miles 750k / 150,000 

Recharge Rate (kW) 0.4 kW 2.4 kW 

Available Energy (CP @1kW) 15 Wh 30 Wh 

Cold Cranking Pulse @ -30°C 4.2 kW 7 V Min. 8 kW 21 V 

Regenerative Pulse N/A N/A 

Discharge Pulse 4.2 kW 2s 6 kW 2

42V Start-St

(FSS)

12V Start-Stop 

(TSS) System Attributes

Selling Price ($/system @ 100k/yr) 40 80 

Maximum System Volume (Liters) 4 8 Maximum System Weight (kg) 5 10 

Survival Temperature Range (°C) -46 to +66 -46 to +66 Operating Temperature Range (°C) -30 to +52 -30 to +52 

Minimum Operating Voltage (Vdc) 9 27 

Maximum Operating Voltage (Vdc) 17 48 

Self Discharge (72hr from Max. V) <4% <4% 

Energy Efficiency on UC10 Load Profile (%) 95 95% Calendar Life (Yrs) 15 15 

Cycle Life and Efficiency Load Profile UC10 UC10 

Cycle Life / Equiv. Road Miles 750k / 150,000 miles 750k / 150,000 

Recharge Rate (kW) 0.4 kW 2.4 kW 

Available Energy (CP @1kW) 15 Wh 30 Wh 

Cold Cranking Pulse @ -30°C 4.2 kW 7 V Min. 8 kW 21 V 

Regenerative Pulse N/A N/A 

Discharge Pulse 4.2 kW 2s 6 kW 2

42V Start-St

(FSS)

12V Start-Stop 

(TSS) System Attributes
6 5th Advanced Automotive Battery Conference

Background (concl.

• In AABC-2004, Continental Temic presented a conc

lead acid batteries and ultracapacitors through DC/

meet the targets of mild hybrids. How does this conwith battery alone solutions in meeting targets?

+

DLCModul

DC

DC DC

EM +

14V

Energy Storage Subsy

EE300-20

AC

Power

DC

DC

UUCap > UBatt

Power

DC

DC

UUCap > UBatt

Pow

conne

DC

DC

UUCap = UBatt

Pow

conne

DC

DC

UUCap = UBatt

Pow

conne

DC

DC

UUCap = UBatt

DC/DC low power

recharge battery (optional)

DC

DC

UUCap > UBatt

DC/DC low power

recharge battery (optional)

DC

DC

UUCap > UBatt
7 5th Advanced Automotive Battery Conference

Motivation for this St

• There is some believe that all the performance, lif

set for energy storage system in mild 42V hybrids 

with advanced batteries.

• What is the potential of dual energy storage syste

combining valve regulated lead acid (VRLA) and meeting the targets?

Battery

Ucaps

Engine
8 5th Advanced Automotive Battery Conference

Objectives

• Develop strategies in analyzing dual vo

storage systems

– Dynamic analysis – equivalent circuit model– Vehicle simulations (ADVISORTM)

• Analyze a combined VRLA and Ucap sy

meeting 42V mild hybrid targets

• Compare VRLA+Ucap with advanced b
9 5th Advanced Automotive Battery Conference

Dynamic Modeling Appr

• Uses existing equivalent-circuit energy stora

ADVISORTM library to model complete syste

• Can be used in stand-alone mode or linked b

model

Key AssumptionPower electronics will not limit dynamic response and will provide requested boost and power transmission levels with some efficiency penalty

ESS2 (Ucaps)

ESS1 (Batteries)
10 5th Advanced Automotive Battery Conference

Selected 42V Power Profiles f

(FreedomCAR 42V Battery Test Manual, DOE/ID-1

• Zero Power Assist 

includes no regen capture

• Full Power Assist 

includes 10s discharge for acceleration

• Drive cycle analysis 

of various profiles and vehicle testing experience indicates regen events are typically longer than 2s

– More likely 4-5s
11 5th Advanced Automotive Battery Conference

Input Parameters

• ESS Model inputs

– VRLA: Hawker Genesis 25 Ah

• SOC Limits: 0.6-0.9• Voltage Limits: 9.5V-16.5V• Mass: 11 kg/module

– Ultracap: Maxwell 2500F

• SOC Limits: 0.5-1.0• Voltage Limits: 1.25V-2.7V• Mass: 0.71 kg/module

• Power electronics inputs

– Mass: 1 kg/kW– Efficiency: f(Power, V1/V2)

• Other ESS 

– Li-ion: Saf

• SOC L• Voltage • Mass: 0

– NiMH: Pa

• SOC L• Voltage • Mass: 
12 5th Advanced Automotive Battery Conference

Power Split Strategies bet

VRLA & Ucap in Combined ES 

• Ucap protects battery from high power tran• Peak power ratings for each system individ

base power split set-point for both charge aevents

• Rate term forces greater portion of power r

the Ucap during transients

• SOC term modifies request to maintain SO

storage devices

• Low power charge and discharge events (b

handled entirely by battery

• Rate term = 5 kW/s

– Transient power requests above this value will be 

the Ucap

– Below this, value are proportionally split between 
13 5th Advanced Automotive Battery Conference

Example of Control Strate

VRLA+Ucap

Bat: do nothing

Ucap: provide power 

for propulsion

Bat: take charge 

energy from ucap

Ucap: discharge to bat

Ucap high

Bat: do nothing unles

needed for power or 

eff op of engine

Ucap: do nothing 

unless needed for 

power or efficient 

operation of engine

Bat:do nothing

Ucap: do nothing 

unless needed for 

power

Ucap mid

Bat: discharge to brin

ucap up to mid pointUcap: don’t discharg

take charge from 

battery

Bat:Don’t discharge unless needed for power, wait for regen

Ucap: Don’t discharge 

unless needed for power, wait for regen

Ucap low

Always accept regen Battery mid 

up to limits. Always 

bring ucap up to mid 

point first, then 

battery.

ucap

Bat: discharge to brin

ucap up to mid point

regen

Battery low
14 5th Advanced Automotive Battery Conference

Evaluating Response of ES 

(attributes considered

• Total Mass (minimize)

– Sum of module masses + 

power electronics mass

• Total Cost (minimize)

– Sum of module costs + 

power electronics cost

• Total Regen (maximize)

– Percentage of regen 

available that is captured

• Total Loss (minimize)

– Combination of ESS and PE 

losses over the cycle

• Time in Red Zone (minimize)

– Sum of time battery is within 

5% of voltage limits, a condition that reduces life

• Other Resp

– Cumulat

• Integ

betweachie

– Peak Tra

• Grea

requepowe

– Average – Min/Max 
15 5th Advanced Automotive Battery Conference

Case Study Summari

Initial Results for Meeting 42V M-

Case Description ESS1_Num ESS2_Num Mass E

# #Kg 

1 Baseline UC – matched 

voltage

20 3 77.2 

2 Reduced UC 7 3 48.5 3 Lead acid only 0 3 33 

4 UC Only 20 0 44.2 5 Optimum. PbA and UC 10.2 5 77.6 6 Optimum PbA, UC, and 6.4 5 69.2 7 Optimum UC only 72 0 159.1 

8 Optimum PbA only 0 7 77 9 Li-ion only 0 30 11.3 

10 NiMH only 0 16 16 
16 5th Advanced Automotive Battery Conference

Initial Results:

Case Study Summaries For 4

• Case 5 and 6 push Ucap-PbA design toward 

more battery to improve cost and reduce red t

• NiMH only case is not the worst or best in any 

but provides a good overall option

• Lightest most efficient system is Li-ion only

Mass Loss Regen

RedZone 

Time

ESS2 Min 

Pwr

ESS2 Max 

Pwr

Cum Tra

Miss

kg Wh -- s kW kW Wh 

77.2 100.6 0.98626 38 -8091.43 6370.43 6.1

48.5 138.7 0.966742 53 -8220.42 7323.59 30.1

33 153.3 0.838809 171 -8609.95 7306.19 89.5

44.2 83.7 0.947857 0.0 0 0 82.7

77.6 110.7 0.995727 9 -12956.4 8395.89 6 

69.2 110.9 0.989705 1 -9480.71 10037.9 20.159.1 73.7 1.00634 0 0 0 5.5

77 110 1 0 -13157.9 13931.2 2.86E

11.3 50.3 0.991295 103 -13157.9 13931.2 3.3

16 68.6 0.994244 94 -13157.9 13931.2 2.2

Mass Loss Regen

RedZone 

Time

ESS2 Min 

Pwr

ESS2 Max 

Pwr

Cum Tra

Miss

kg Wh -- s kW kW Wh 

77.2 100.6 0.98626 38 -8091.43 6370.43 6.1

48.5 138.7 0.966742 53 -8220.42 7323.59 30.1

33 153.3 0.838809 171 -8609.95 7306.19 89.5

44.2 83.7 0.947857 0.0 0 0 82.7

77.6 110.7 0.995727 9 -12956.4 8395.89 6 

69.2 110.9 0.989705 1 -9480.71 10037.9 20.159.1 73.7 1.00634 0 0 0 5.5

77 110 1 0 -13157.9 13931.2 2.86E

11.3 50.3 0.991295 103 -13157.9 13931.2 3.3

16 68.6 0.994244 94 -13157.9 13931.2

Mass Loss Regen

RedZone 

Time

ESS2 Min 

Pwr

ESS2 Max 

Pwr

Cum Tra

Miss

kg Wh -- s kW kW Wh 

77.2 100.6 0.98626 38 -8091.43 6370.43 6.1

48.5 138.7 0.966742 53 -8220.42 7323.59 30.1

33 153.3 0.838809 171 -8609.95 7306.19 89.5

44.2 83.7 0.947857 0.0 0 0 82.7

77.6 110.7 0.995727 9 -12956.4 8395.89 6 

69.2 110.9 0.989705 1 -9480.71 10037.9 20.159.1 73.7 1.00634 0 0 0 5.5

77 110 1 0 -13157.9 13931.2 2.86E

11.3 50.3 0.991295 103 -13157.9 13931.2 3.3

16 68.6 0.994244 94 -13157.9 13931.2 2.2

Case Description ESS1_Num ESS2_Num

# #

1

Baseline -matched voltages 20 3

2 Reduced UC 7 33 Lead acid only 0 3

4 UC only 20 0

5 Opt. PbA and UC 10.2 56

Opt. PbA, UC, and fixed split ratio 6.4 5

7 Opt. UC only 72 0

8 Opt. PbA only 0 7

9 Li-ion only 0 30

10 NiMH only 0 16

Case Description ESS1_Num ESS2_Num

# #

1

Baseline -matched voltages 20 3

2 Reduced UC 7 33 Lead acid only 0 3

4 UC only 20 0

5 Opt. PbA and UC 10.2 56

Opt. PbA, UC, and fixed split ratio 6.4 5

7 Opt. UC only 72 0

8 Opt. PbA only 0 7

9 Li-ion only 0 30

10 NiMH only 0 16

Case Description ESS1_Num ESS2_Num

# #

1

Baseline -matched voltages 20 3

2 Reduced UC 7 33 Lead acid only 0 3

4 UC only 20 0

5 Opt. PbA and UC 10.2 56

Opt. PbA, UC, and fixed split ratio 6.4 5

7 Opt. UC only 72 0

8 Opt. PbA only 0 7

9 Li-ion only 0 30

10 NiMH only 0 16

Mass Loss Regen

RedZone 

Time

ESS2 Min 

Pwr

ESS2 Max 

Pwr

Cum Tra

Miss

kg Wh -- s kW kW Wh 

77.2 100.6 0.98626 38 -8091.43 6370.43 6.1

48.5 138.7 0.966742 53 -8220.42 7323.59 30.1

33 153.3 0.838809 171 -8609.95 7306.19 89.5

44.2 83.7 0.947857 0.0 0 0 82.7

77.6 110.7 0.995727 9 -12956.4 8395.89 6 

69.2 110.9 0.989705 1 -9480.71 10037.9 20.159.1 73.7 1.00634 0 0 0 5.5

77 110 1 0 -13157.9 13931.2 2.86E

11.3 50.3 0.991295 103 -13157.9 13931.2 3.3

16 68.6 0.994244 94 -13157.9 13931.2 2.2

Mass Loss Regen

RedZone 

Time

ESS2 Min 

Pwr

ESS2 Max 

Pwr

Cum Tra

Miss

kg Wh -- s kW kW Wh 

77.2 100.6 0.98626 38 -8091.43 6370.43 6.1

48.5 138.7 0.966742 53 -8220.42 7323.59 30.1

33 153.3 0.838809 171 -8609.95 7306.19 89.5

44.2 83.7 0.947857 0.0 0 0 82.7

77.6 110.7 0.995727 9 -12956.4 8395.89 6 

69.2 110.9 0.989705 1 -9480.71 10037.9 20.159.1 73.7 1.00634 0 0 0 5.5

77 110 1 0 -13157.9 13931.2 2.86E

11.3 50.3 0.991295 103 -13157.9 13931.2 3.3

16 68.6 0.994244 94 -13157.9 13931.2

Mass Loss Regen

RedZone 

Time

ESS2 Min 

Pwr

ESS2 Max 

Pwr

Cum Tra

Miss

kg Wh -- s kW kW Wh 

77.2 100.6 0.98626 38 -8091.43 6370.43 6.1

48.5 138.7 0.966742 53 -8220.42 7323.59 30.1

33 153.3 0.838809 171 -8609.95 7306.19 89.5

44.2 83.7 0.947857 0.0 0 0 82.7

77.6 110.7 0.995727 9 -12956.4 8395.89 6 

69.2 110.9 0.989705 1 -9480.71 10037.9 20.159.1 73.7 1.00634 0 0 0 5.5

77 110 1 0 -13157.9 13931.2 2.86E

11.3 50.3 0.991295 103 -13157.9 13931.2 3.3

16 68.6 0.994244 94 -13157.9 13931.2 2.2

Case Description ESS1_Num ESS2_Num

# #

1

Baseline -matched voltages 20 3

2 Reduced UC 7 33 Lead acid only 0 3

4 UC only 20 0

5 Opt. PbA and UC 10.2 56

Opt. PbA, UC, and fixed split ratio 6.4 5

7 Opt. UC only 72 0

8 Opt. PbA only 0 7

9 Li-ion only 0 30

10 NiMH only 0 16

Case Description ESS1_Num ESS2_Num

# #

1

Baseline -matched voltages 20 3

2 Reduced UC 7 33 Lead acid only 0 3

4 UC only 20 0

5 Opt. PbA and UC 10.2 56

Opt. PbA, UC, and fixed split ratio 6.4 5

7 Opt. UC only 72 0

8 Opt. PbA only 0 7

9 Li-ion only 0 30

10 NiMH only 0 16

Case Description ESS1_Num ESS2_Num

# #

1

Baseline -matched voltages 20 3

2 Reduced UC 7 33 Lead acid only 0 3

4 UC only 20 0

5 Opt. PbA and UC 10.2 56

Opt. PbA, UC, and fixed split ratio 6.4 5

7 Opt. UC only 72 0

8 Opt. PbA only 0 7

9 Li-ion only 0 30

10 NiMH only 0 16
17 5th Advanced Automotive Battery Conference

Comparing Dual ESS Op

(Existing Technologie

• High voltage Battery

– Cost = 

$90+$250+PE_var+UC=$340+...

– Mass = 

33+3.75+PE_var+UC=36.75+...

– Volume = 

11.6+4.1+PE_var+UC=15.7+...

• High voltage 

– Cost = 

$500+$25

• Maybe 

$500+...

– Mass = 

14.2+3.75

– Volume = 

12.2+4.1+

• Other technologies

– Li-ion

• Cost = $440-$880• Mass = 8-17 kg• Volume = 7-13 L

– NiMH

• Cost = $400-$1• Mass = 10-30 k• Volume = 9-26 
18 5th Advanced Automotive Battery Conference

Cost Comparison

0 200 400 600 800 

Cost ($)

High Voltage Ucap

High Voltage Battery

Li-ion

NiMH

Ucap + Battery (no PE)

Technology Options
19 5th Advanced Automotive Battery Conference

Mass Comparison

0 10 20 30 40 50 60 

Mass (kg)

High Voltage Ucap

High Voltage Battery

Li-ion

NiMH

Ucap + Battery (no PE)

Technology Options
20 5th Advanced Automotive Battery Conference

Volume Comparison

0 5 10 15 20 25 

Volume (L)

High Voltage Ucap

High Voltage Battery

Li-ion

NiMH

Ucap + Battery (no PE)

Technology Options
21 5th Advanced Automotive Battery Conference

0 10000 20000 30000 40000 50000 60000 

Cycle Life (#)

High Voltage Ucap

High Voltage Battery

Li-ion

NiMH

Ucap + Battery (no PE)

Technology Options

Cycle Life Compariso

**Note: UCap solution does not meet all per
22 5th Advanced Automotive Battery Conference

Observations and Summ

• Having a high voltage UCap based system seem

potential for minimizing the system cost. The fixthe cost is large and the variable part is small.

• The fixed attributes of either PbA+UCap approa

less attractive than other advanced energy stora

• If power electronics base costs can be cut in ha

go to 0.5 cents/F then these systems maybe comon cost, less so on mass and volume.

• Incremental mass of PbA+UCap system is ~25k

in ~1% decrease in fuel economy with all other tequal.

• Operating efficiency of UCap and other technolo

PbA significantly lower. Therefore, PbA+UCap s

less efficient than other technologies.

• Future work to include drive cycle analysis for p
23 5th Advanced Automotive Battery Conference

Acknowledgements

• Sponsored by U.S. Department of Energy

FreedomCAR and Vehicle Technologies.

– Tien Duong– Dave Howell

• Appreciate the support and technical guid

USABC/FreedomCAR ES Technical Team

• Appreciate technical discussions and guid

Dr. Menahem Anderman of AAB

www.ctts.nrel.gov/BTM

www.ctts.nrel.gov/analysis