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
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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