Plug-In HEV Vehicle Design Options and Expectations

ZEV Technology SymposiumCalifornia Air Resources Board

Sacramento, CA

September 27, 2006

Tony MarkelNational Renewable Energy Laboratory

With support from FreedomCAR and Vehicle Technologies Program

Office of Energy Efficiency and Renewable Energy U.S. Department of Energy

NREL/PR-540-40630

2

Key Messages

• There are many ways to design a PHEV …— the best design depends on your objective

• PHEVs provide potential for petroleum displacement through fuel flexibility

— what are the cost and emissions tradeoffs

• PHEV design space has many dimensions— simulation being used for detailed exploration

• Simulations using real-world travel data provides early glimpse into in-use operation

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PHEV Stakeholder Objectives

ConsumersConsumersAffordable

Fun to driveFunctional

California Gov.California Gov.Reduced air pollution

US Gov./DOEUS Gov./DOEReduced petroleum use

Auto ManufacturerAuto ManufacturerSell cars

Electric UtilityElectric UtilitySell electricity

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A Plug-In Hybrid-Electric Vehicle (PHEV)

ELECTRIC ACCESSORIES

ADVANCED ENGINE

ENGINE IDLE-OFF

ENGINE DOWNSIZING

REGENERATIVE BRAKING

BATTERY RECHARGE

ELECTRICITY

PETROLEUM

AND/OR

Fuel Flexibility

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Some PHEV DefinitionsCharge-Depleting (CD) Mode: An operating mode in which the energy storage SOC

may fluctuate but on-average decreases while driving

Charge-Sustaining (CS) Mode: An operating mode in which the energy storage SOC may fluctuate but on-average is maintained at a certain level while driving

All-Electric Range (AER): After a full recharge, the total miles driven electrically (engine-off) before the engine turns on for the first time.

Electric Vehicle Miles (EVM): After a full recharge, the cumulative miles driven electrically (engine-off) before the vehicle reaches charge-sustaining mode.

Charge-Depleting Range (CDR): After a full recharge, the total miles driven before the vehicle reaches charge-sustaining mode.

Blended Strategy: A charge-depleting operating strategy in which the engine is used to supplement battery/motor power.

PHEV20: A PHEV with useable energy storage equivalent to 20 miles of driving energy on a reference driving cycle. A PHEV20 can displace petroleum energy equivalent to 20 miles of driving on the reference cycle with off-board electricity.

NOTE: PHEV20 does not imply that the vehicle will achieve 20 miles of AER, EVM or CDR on the reference cycle nor any other driving cycle. Operating characteristics also depend on the power ratings of components, the powertrain control strategy and the nature of the driving cycle

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Battery Definition as Key Input to Simulation

kWh/mi(from simulation)

SOC window

PHEV range

P/E ratio

Performance constraints

kWh usable

kWh total

kWmotor

kWengine

DOH

Benefit of plugging-in

Benefit of hybridization

Total MPG Benefit

mass compounding

Input parameters that define the battery in BLUE

DOH = degree of hybridization

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Batteries in Current PHEVs

Johnson Controls/SAFT

Varta

Valence Technology

Kokam

A123 Systems

Electro Energy Inc.

NiM

HC

o/N

i bas

edLi

-Io

nIr

on

pho

sph

ate

base

d Li

-Io

n

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Battery SOC Design Window

Battery cycle life is a strong function of SOC swing:

In setting requirements, we must have realistic expectations for battery SOC design window because of the impacts on total battery size and life.

SOC design window is a key factor in battery sizing: windowSOC

kWhkWh useabletotal

=

Daily Mileage Probability Distribution

0%

5%

10%

15%

20%

25%

0 10 20 30 40 50 60 70 80 90 100

Daily mileage (<= mi)

Prob

abilit

y (%

)

Battery SOC swing is a strong function of driving habits:

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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 10 20 30 40 50 60

Daily Mileage / PHEVx

Design SOC window based on PHEVx

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 10 20 30 40 50 60

Daily Mileage / PHEVx

Average daily SOC swing based on daily mileage distribution

Daily mileage probability distribution

Battery SOC Design Window

Battery SOC design curve for 15 year cycle life

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Operating Strategy OptionsAll-Electric or Blended

• Engine turns on when power exceeds battery power capability

• Engine only provides load that exceeds battery power capability

• Engine turns on when battery reaches low state of charge

• Requires high power battery and motor

-30

-20

-10

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35 40Distance (mi)

Pow

er (k

W)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

SOC

(%)

enginemotorSOC

All-Electric

-30

-20

-10

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35 40Distance (mi)

Pow

er (k

W)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

SOC

(%)

enginemotorSOC

Blended

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Real Driving Survey Data• Provides valuable insight into travel behavior• GPS augmented surveys supply details needed

for vehicle simulation

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• St. Louis data set includes 227 vehicles from 147 households• Complete second by second driving profile for one day• 8650 miles of travel• St. Louis data set is a small sample of real data • NPTS data is generated from mileage estimates

St. Louis Travel Data AnalysisDaily Driving Distance Similar to 1995 NPTS Data

0

2

4

6

8

10

12

0 0-55-1010

-15

15-20

20-2

525

-30

30-3

535

-40

40-45

45-50

50-55

55-6

060

-65

65-7

070-

7575

-80

80-8

585

-90

90-9

595

-100

Daily Distance (mi)Fr

eque

ncy

(%)

0

10

20

30

40

50

60

70

80

90

100

Cum

mul

ativ

e Fr

eque

ncy

(%)

1995 NPTS Data

~33 mi0

1

2

3

4

5

6

7

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98100

Daily Travel Distance (miles)

Freq

uenc

y (%

)

0

10

20

30

40

50

60

70

80

90

100

Cum

ulat

ive

Freq

uenc

y (%

)

Frequency (%)Cumulative Freq. (%)

~29 mi

St. Louis HHTS Data

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Consumption DistributionMany PHEVs Better than Rated Values

0 5 10 15 20 250

10

20

30

40

Fuel Consumption (L/100km)

Perc

enta

ge o

f Fle

et (%

)

Conventional

0 5 10 15 20 250

10

20

30

40

Fuel Consumption (L/100km)

Perc

enta

ge o

f Fle

et (%

)

Hybrid

0 5 10 15 20 250

10

20

30

40PHEV20

Fuel Consumption (L/100km)

Per

cen

tag

e o

f Fle

et (%

)

0 5 10 15 20 250

10

20

30

40

Fuel Consumption (L/100km)

Perc

enta

ge o

f Fle

et (%

)

PHEV40

Real-world

City/HighwayComposite

39.2 mpg (6.0 L/100km)

US0633.2 mpg (7.1 L/100km)

Real-world

City/HighwayComposite

67.4 mpg (3.49 L/100km)

City/HighwayComposite

54 mpg (4.35 L/100km)

US0651.5 mpg (4.57 L/100km)

US0639.6 mpg (5.94 L/100km)

Real-worldReal-world

City/HighwayComposite

26 mpg (9.05 L/100km)

US0624.6 mpg (9.55 L/100km)

“Fleet” results are based on simulations of 227 vehicle driving profiles from St. Louis metropolitan area.

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0 5 10 15 20 25 300

5

10

15

20

25

30

35

40

Time of Day (hr)

Per

cen

tag

e o

f V

ehic

le F

leet

In U

se (

%)

0 5 10 15 20 25 300

50

100

150

200

250

300

350

400

Cu

mu

lati

ve F

uel

Co

nsu

med

(g

allo

ns)

ConventionalHybridPHEV20PHEV40

PHEVs Reduce Fuel Consumption By >50% On Real-World Driving Cycles

• 8647 total miles driven• 100% replacement of

sample fleet

227 vehicles from St. Louis each modeled as a conventional, hybr227 vehicles from St. Louis each modeled as a conventional, hybrid and PHEVid and PHEV

26 mpg

58 mpg & 140 Wh/mi

PHEVs:>40% reduction in energy

costs>$500 annual savings

37 mpg

76 mpg & 211 Wh/mi

Assumes $2.41/gal and 9¢/kWh

$1.21

$1.58

$2.48

$3.45

Gas.

Average Daily Costs

$0.72

$0.48

---

---

Elec.

5.1

5.4

6.5

9.1

¢/mi

PHEV40

PHEV20

HEV

CV

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Simulated In-Use All-Electric Range Distribution

• Vehicles were designed to operate all electrically on UDDS

• Power demands of real profiles exceed UDDS peak power within the first few miles

1 3 5 7 9 11 13 15 17 19 21 23 250

5

10

15

20

25

30

All Electric Range (mi)

Per

cent

age

of F

leet

(%

)

PHEV20

0 5 10 15 20 25 30 35 400

5

10

15

20

25

30

35

40

All Electric Range (mi)

Per

cent

age

of F

leet

(%

)

PHEV40

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Fuel Economy and All-Electric Range Comparison

• Significant difference between rated (EPA drive cycles) and real-world median values for PHEVs

— Consumers likely to observe fuel economy higher than rated value in daily driving

— Vehicles designed with all-electric range likely to operate in a blended mode to meet driver demands

** Fuel economy values do not include electrical energy consumption

Rated Median Rated MedianConventional 26 24.4 n/a n/aHEV 39.2 35.8 n/a n/aPHEV20 54 70.2 22.3 5.6PHEV40 67.4 133.6 35.8 3.8

Fuel Economy (mpg) ** All Electric Range (mi)

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PHEV20 Savings Relative to Conventional and HEV

• Savings relative to conventional are almost entirely distance dependent

• Savings relative to HEV are distance dependent up to PHEV distance then constant

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Insights:

The PHEV20s that saved the most fuel relative to an HEV travel ~25 miles with speeds under 60 mph and light accelerations

The PHEV20s that saved the least fuel relative to the HEV in the 20-30 mile range had periods of 60+ mph highway driving and the accelerations were significantly more aggressive

Most Savings Least Savings

Deep Dive into Real-World PHEV Simulations

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Summary and Conclusions

• PHEVs provide petroleum displacement through fuel flexibility

• Design needs to consider a spectrum of stakeholder objectives

• Analysis of real-world travel behavior provides perspective on design challenges

— Vehicles designed as all-electric likely to operate as blended— What’s emissions impact of real-world blended operation

• In-use petroleum displacement not tied to all-electric range

— Consider energy equivalent all-electric range• PHEV benefit is strongly related to distance and

aggressiveness of real-world usage