Optimization of Fuel Cell Vehicle Fuel Economy - Presentations... · Optimization ofOptimization of Fuel Cell Vehicle Fuel Economy October 2004 AiRAymeric Rousseau Phil Sharer Rajesh

Optimization of Fuel Cell Vehicle FuelOptimization of Fuel Cell Vehicle Fuel Economy

October 2004

A i RAymeric RousseauPhil Sharer

Rajesh AhluwaliaArgonne National LaboratoryArgonne National Laboratory

Sponsored by Lee Slezak (U.S. DOE)

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Fuel Cell Vehicle Fuel Economy OptimumOptimum

Study Scope

Hybridization Degree

Energy Storage TechnologyEnergy Storage Technology

Control Strategy

i Perspectives

2

Fuel Cell Vehicle Fuel Economy OptimizationOptimization

St d S Study Scope


Energy Storage Technology

Control StrategyControl Strategy

Perspectives

3

FreedomCAR FCV Energy Storage Proposed Goals Spring 2003 Proposed Goals Spring 2003

FreedomCAR Goals Low Power High Power Characteristics Units Energy Storage Energy Storage

Pulse Discharge Power (10s) kW 25 50 M R P l (5 ) kW 30 60Max Regen Pulse (5s) kW 30 60Total Available Energy kWh 1.5 3 Round Trip Efficiency % >90 >90 Cycle Life Cyc. TBD (15 year life equiv.) TBD (15 year life equiv.)Cold-start at -30°C (TBD kW for TBD min.) kW 5 5Cold start at 30 C (TBD kW for TBD min.) kW 5 5Calendar Life Yrs 15 15 Max Weight kg 40 65 Max Volume liters 32 50 Production Price @ 100k units/yr $ 500 1,000 M i O ti V lt Vd </ 440 </ 440Maximum Operating Voltage Vdc </= 440 max </= 440 maxMinimum Operating Voltage Vdc >/= 0.5 x Vmax >/= 0.5 x Vmax Maximum Self Discharge Wh/d 50 50 Operating Temperature °C -30 to +52 -30 to +52 Survival Temperature °C -46 to +66 -46 to +66

4

p

Structure of the Study

Hybridization HotCurrent FCHybridizationDegrees

FUDS

ESSSUV Mid-Term FC FHDS AmbESSTechnologies

C t lCar Future FC US06 ColdControlStrategies

5

Fuel Cell HEV ConfigurationFuel Cell HEV Configuration

DC Link

6

Major Assumptionsj p Vehicle and Performance

– Mid‐size SUV (Explorer, Durango, Blazer)

– Target 0‐60 mph acceleration in 10.2 s g p

– 55 mph at grade of 6.5% continuous (a least 20 minutes)

– Top speed of 100 mph

Fuel Cell System Requirements y q

– Fuel cell should be sized to provide a least power for top speed and grade performance

– FCS must have 1‐s transient response time for 10% to 90% power.

– FCS should reach maximum power in 15 s for cold start from 20C ambient temperature and in 30 s for cold start from ‐20C ambient temperature

Power Requirements (based on PSAT simulations)

– 160kW peak power for 0‐60 mph acceleration

– Minimum fuel cell power of 80kW for achieving speed at 6.5% grade

Default: tight SOC control, lithium‐ion, FUDS

7

Detailed Models Necessary for l hRealistic Behavior

(%)

ffici

ency

Fuel Cell System Efficiencyyste

m E

ff

Fuel Cell System Efficiency is Not a Monotonic Function of Power Demand

l Cel

l Sy

Fuel

8

Power Demand (kW)

Design-Specific FC System Modeling R i d t A C t I tRequired to Assess Component Impact

Electric Hydrogen

Process Water

Coolant

Electric Motor

Hydrogen Tank

PEFC

Humidified Air

Humidifier Heater

PEFCStack

Humidified Hydrogen

Demister

Radiator & Condenser

Fan

Compressor/Motor/Expander

AirExhaust

Water TankCondensate

Pump

9

Small Differences in Components Can Have Large System ImplicationsSystem Implications

(%)

ffici

ency

ys

tem

Eff

l Cel

l Sy

Fuel

10

Power Demand (kW)

Design-Specific Models Required for Realistic FC Cycle Efficiency

64.5

cy (%

)

FUDS Cycle

63 5

64

ency

(%)

Effic

ienc

63

63.5

Cyc

le E

ffici

em

Cyc

le E

62

62.5

Cel

l Sys

tem

Cl S

yste

m

61

61.5Fuel

CFu

el C

ell

11

61FC HEV 140kW FC HEV 120kW FC HEV 100kW FC HEV 80kW

F


St d S Study Scope




Perspectives

12

Increase in Hybridization Degree Can Lead to Decrease in Fuel Economy

65

mpg

e)

50*37.5*

25*FUDS Cycle

60

. (m

pge)

e Eq

. (m

12.5*

55

Gas

olin

e Eq

.G

asol

ine

50

el E

cono

my

Gco

nom

y

0*

40

45Fue

Fuel

Ec

13

*Hybridization Degree

40FC HEV 160kW FC HEV 140kW FC HEV 120kW FC HEV 100kW FC HEV 80kW

Because the Regen Energy Increase is Nullified by the FC Efficiency Decrease

84.590 FC system effPercentage regen braking

FUDS Cycle

y

64.0 63.660.9 63.0

72.2

62.270

80

38.550

60

20

30

40

0

10

20

14

0FC HEV 140kW FC HEV 120kW FC HEV 100kW FC HEV 80kW

Hybridization Results

• Key benefit of hybridization is fuel economy increase for FUDS h k i b kiFUDS thanks to regenerative braking

• Increasing the hybridization degree is interesting until theIncreasing the hybridization degree is interesting until the additional gain is nullified by the decrease in fuel cell efficiency

For Li‐ion it is better to limit the ESS power to 40kW toFor Li‐ion, it is better to limit the ESS power to 40kW to preserve FC system efficiency while capturing most available regen energy

15


St d S Study Scope




Perspectives

16

Optimum Hybridization Degree d h h l

62.5

63

ge)

Depends upon the ESS Technology

mpg

e) FUDS Cycle

61.5

62

ne E

q (m

pg

Li-ione Eq

. (m

60

60.5

61

my

Gas

olin

Li ionNiMHUltracap

Gas

olin

e

59

59.5

60

el E

cono

mco

nom

y

58

58.5

140 120 100 80

Fue

Fuel

Ec

17

Fuel Cell Power (kW)

NiMH and Ultracap have lower specific power than Li-ionpower than Li ion

Relative comparison of vehicle test mass for each energy storage technology (Reference Li-ion)

1 10

1.08

1.09

1.10

NiMH

Ultracap

1.05

1.06

1.07

Rel

ativ

e M

ass

1 02

1.03

1.04

R

The fuel economy penalty due to mass increase is lower for a low hybridization degree

1.02140 120 100 80

Fuel Cell Power (kW)

18

hybridization degree

NiMH and Ultracap allow better regenerative braking recovery at low hybridization degreebraking recovery at low hybridization degree

FUDS Cycle - Comparison of regenerative braking energy recovered

100Due to the

90

95ve

ene

rgy

)

Due to the need to size the ultracapf Z60 f

75

80

85

e of

rege

nera

tivre

cove

red

(%) Li-ion

NiMHUltracap

for Z60 for energy

65

70

Perc

enta

ge

Small ess strategy ; SOCtarget = 0 5

60140 120 100 80

Fuel Cell Power(kW)

19

Small ess strategy ; SOCtarget = 0.5

The SOC varies more for the Li-ion 6Ah, decreasing the maximum charge power

3.5

4x 104 Comparison of Maximum Charge Power

Li-ionNiMH

2

2.5

3

tery

Pow

er

0.5

1

1.5Bat

t

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90

Battery SOC

20

Energy Storage Technology Results

• Optimum hybridization degree depends on energy storage technology

• Specific power and specific energy characteristics are key• Specific power and specific energy characteristics are key to optimum fuel economy

For Li‐ion a higher hybridization degree is necessary while both NiMH and ltracapacitors achie e best res lts atboth NiMH and ultracapacitors achieve best results at very low hybridization degrees

21


St d S Study Scope




Perspectives

22

Default Control Strategy Maximizes Fuel Cell System Usey

23

Control Strategies Options Considered Considered Use the fuel cell as main power source

– SOCtarget = 0.7• Min fuel cell power demand = 0 (Default Control)

• Min fuel cell power demand = 5kW


– SOCtarget = 0.5• Min fuel cell power demand = 0

Mi f l ll d d 15kW• Min fuel cell power demand = 15kW

Use the battery as main power source– SOCtarget = 0.7

SOC 0 5– SOCtarget = 0.5

With min fuel cell power demand = Pwheel + P(SOC)

24

Impact of fuel cell power min on battery power battery power

25

30Pminfc=0

25

30Pminfc=15kW

10

15

20

25

10

15

20

25

-5

0

5

-5

0

5

-20

-15

-10 veh spdfc pwr kWess pwr kW

-20

-15

-10 veh spdfc pwr kWess pwr kW

640 645 650 655 660 665 670 675 680-25

640 645 650 655 660 665 670 675 680-25

1 – Battery provides 2 – FC provides more 3 – Regen amount in

25

1 – Battery provides more power during a longer period

2 FC provides more power to recharge the battery

3 Regen amount in unchanged

Impact of fuel cell power min on battery SOCbattery SOC

75Im pact o f Min FC Power on SO C window

Pfcm in=0

73

74

P fcm in 0P fcm in=5kWPfcm in=15kW

71

72

SO

C (%

)

69

70

Bat

tery

S

67

68

26

0 200 400 600 800 1000 1200 140066

T im e(sec)

Increasing the min fuel cell power demand leads to fuel economy penaltyy p y

58 Example of 80kW FC58 Example of 80kW FC57.2

57.157.5

(mpg

)

57.257.157.5

(mpg

)

56.5

56.5

57

Com

paris

on

56.5

56.5

57

Com

paris

on

55 5

56

uel E

cono

my

55 5

56

uel E

cono

my

55

55.5Fu

0kW 5kW 15kW55

55.5Fu

0kW 5kW 15kW

27

Because the increase in regen energy is nullified by the decrease in fuel cell efficiency

84.50 85.3088.10100

Reference Control Strategy (SOC=0.7, Different Pfcdmd, 80kW FC)

62.2 61.9 60.770

80

90

50

60

70

20

30

40

FC system effPercentage regen braking

0

10

20

0kW 5kW 15kW

28

0kW 5kW 15kW

Summary Table – Example of 80kW fuel cell system (SOCtarget = 0 7)cell system (SOCtarget = 0.7)

Units 0kW 5kW 15kWMech. Braking

Energy Loss Wh 106 100 76Fuel Cell

Wh 1818 1839 1906Energy Loss Wh 1818 1839 1906Difference Wh 14.9 57.7

29

Control Strategies Options d dConsidered

Use the fuel cell as main power source– SOCtarget = 0.7

• Min fuel cell power demand = 0 (Default Control)








30

Impact of target battery SOC on p g ybattery power

30

SOC = 0.7; Pminfc=15kW

veh spdfc pwr kW

kW30

SOC = 0.5; Pminfc=15kW

veh spdfc pwr kW

kW

20

ess pwr kW

20

ess pwr kW

0

10

0

10

-10 -10

640 645 650 655 660 665 670 675 680

-20

640 645 650 655 660 665 670 675 680

-20

2 – Battery provides 3 – FC does not need 1 – Increased regen

31

2 – Battery provides more power during a longer period

3 FC does not need to recharge the battery

1 Increased regen amount

A smaller target SOC (0.5) leads to fuel economy benefits

59.360

Impact of initSOC and Pfc min on FE - 80kW fceconomy benefits

57.3

58.1

58

59

on (m

pg)

56.557

58

y C

ompa

riso

55

56

Fuel

Eco

nom

y

54

F

SOC = 0.7; Pfcmin=0

SOC = 0.5; Pfcmin=0

SOC = 0.7; Pfcmin=15kW

SOC = 0.5Pfcmin=15kW

32

Control Strategies Options Considered

Use the fuel cell as main power source– SOCtarget = 0.7

• Min fuel cell power demand = 0 (Default Control)








33

US06 Cycle Could Benefit From Using More The Battery

57.5

80kW

More The Battery

mpg

e)

56.5

57

on (m

pg) 80kW

100kW FC120kW FC

e Eq

. (m

55.5

56

Com

paris

oG

asol

ine

54.5

55

Econ

omy

Cco

nom

y

53 5

54

54.5

Fuel

EFu

el E

c

34

53.5FC main source - SOC = 0.7 ESS main source - SOC = 0.7

Use more the battery

Control Strategy Results

• For the same control strategy, it is possible to increase losses by increasing the regenerative braking due to fuellosses by increasing the regenerative braking due to fuel cell efficiency

• Rather than increasing the minimum fuel cell power demand minimizing the target SOC is a better way todemand, minimizing the target SOC is a better way to increase the regenerative braking

1 ‐ Low SOC should be targeted to increase regen capture2 – Optimum control strategy philosophy depends upon driving cycle: For FUDS, it is better not to use the battery too much whereas it is the opposite for US06

35

too much, whereas it is the opposite for US06

System Approach is Needed to Achieve Optimum Fuel EconomyOptimum Fuel Economy

• Key benefit of hybridization is fuel economy increase for FUDS thanks to regenerative brakingthanks to regenerative braking

• Optimum hybridization degree is energy storage technology dependant

• Fuel cell system efficiency and regenerative braking trade‐off is key to optimum fuel economy‐ Increasing hybridization degree and SOC window can lowerIncreasing hybridization degree and SOC window can lower fuel economy

‐ Minimizing SOC target is a good way to increase the regenerative brakingregenerative braking

36

Optimization of Fuel Cell Vehicle Fuel Economy - Presentations... · Optimization ofOptimization of Fuel Cell Vehicle Fuel Economy October 2004 AiRAymeric Rousseau Phil Sharer Rajesh

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