Plug-In HEV Vehi

Options and Ex

ZEV Technol

Californ

National Renewa

FreedomCAR and 

Office of Energy Ef

NREL/PR-540-40630
2

Key 

• There are many ways to design a P

— the best design depends on your obj

• PHEVs provide potential for petroleu

displacement through fuel flexibility

— what are the cost and emissions trad

• PHEV design space has many dime

— simulation being used for detailed ex

• Simulations using real-world travel d

early glimpse into in-use operation
3

PHEV Stakeholder 

Consumers Consumers

Affordable

Fun to drive

Functional

Ca

Ca

Red

US Gov./DOE US Gov./DOE

Reduced petroleum use

Auto Manufacturer Auto Manufacturer

Sell cars

Electric U

Electric U

Sell electri
4

A Plug-In Hybrid-Electric Veh

ADVANCED ENGINE

ENG

ENGINE DOWNSIZING

REGENERATIVE BRAKING

ELECTRICITY

PETROLEUM

AND/OR

Fuel Flexibility
5

Some PHEV 

Charge-Depleting (CD) Mode: An operating mode in which the 

may fluctuate but on-average decreases while driving

Charge-Sustaining (CS) Mode: An operating mode in which the 

may fluctuate but on-average is maintained at a certain level w

All-Electric Range (AER): After a full recharge, the total miles d

(engine-off) before the engine turns on for the first time.

Electric Vehicle Miles (EVM): After a full recharge, the cumulati

electrically (engine-off) before the vehicle reaches charge-susta

Charge-Depleting Range (CDR): After a full recharge, the total 

vehicle reaches charge-sustaining mode.

Blended Strategy: A charge-depleting operating strategy in whic

supplement battery/motor power.

PHEV20: A PHEV with useable energy storage equivalent to 20 

on a reference driving cycle. A PHEV20 can displace petroleu

20 miles of driving on the reference cycle with off-board electric

NOTE: PHEV20 does not imply that the vehicle will achieve 20 m

CDR on the reference cycle nor any other driving cycle. Operadepend on the power ratings of components, the powertrain conature of the driving cycle
6

Battery Definition as Key Input 

kWh/mi(from simulation)SOC windowPHEV rangeP/E ratioPerformance constraints

kWh usable

kWh total

kWmotorkWengine

DOH

Tot

mass compounding

Input parameters tha

DOH = degree of hybridization
7

Batteries in Cur

Johnson Controls/SAFT

Varta

Valence Technology

A

Electr

NiMH Co/Ni based

Li-Ion

Iron phosphate 

based Li-Ion
8

Battery SOC Desi

Battery cyc

function o

In setting requirements, we must have realistic expe

SOC design window because of the impacts on total 

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

k

kWh 

total =

Daily Mileage Probability Distribution

0%5%

10%15%20%25%

0 10 20 30 40 50 60 70 80 90 100

Daily mileage (<= mi)

Probability (%)

Battery SOC swing is a strong 

function of driving habits:
9

0%

10%20%30%40%50%60%70%80%90%

100%

0 10 20 30 40 

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 

Daily Mileage / PHEVx

Averaswing milea

Daily mileage probability distribution

Battery SOC Desi

Battery SOC design curve for 15 year cycle 
10

Operating Stra

All-E

• Engine turns on when power 

exceeds battery power capability

• Engine only provides load that 

exceeds battery power capability

• Engine turns 

reaches low 

• Requires hig

motor

-30-20-10

0

10203040506070

0 5 10 15 20 25 30 35 40

Distance (mi)

Power (kW)

0%10%20%30%40%50%60%70%80%90%100%

SOC (%)

enginemotorSOC

All-Electric

-30-20-10

0

10203040506070

0 5 10 15 

D

Power (kW)
11

Real Driving S

• Provides valuable insight into travel • GPS augmented surveys supply de

for vehicle simulation
12

• St. Louis data set includes 227 vehicles from 147 h• Complete second by second driving profile for one • 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 Da

Daily Driving Distance Similar t

02468

1012

00-55-10 10-15 15-2020-25 25-30 30-35 35-40 40-45 

Daily 

Frequency (%)

1995 

~33 

01234567

2468101214161820222426283032343638404244464850525456586062646668707274767880828486889092949698100

Daily Travel Distance (miles)

Frequency (%)

0102030405060708090100

Cumulative Frequency (%) Frequency (%) Cumulative Freq. (%)

~29 mi

St. Louis HHTS Data
13

Consumption D

Many PHEVs Better tha

0

5 10 15 20 25

0

10203040

Fuel Consumption (L/100km)

Percentage of Fleet (%)

Conventional

0

5 10 

0

10203040

Fuel Consump

Percentage of Fleet (%)

Hyb

0

5 10 15 20 25

0

10203040

PHEV20

Fuel Consumption (L/100km)

Percentage of Fleet (%)

0

5 10 

0

10203040

Fuel Consump

Percentage of Fleet (%)

PHE

Real-world

39.

33

R

67.4 m

City/Highway

Composite

54 mpg (4.35 L/100km)

51.5 m

US06

39.6 mpg (5.94 L/100km)

Real-world Rea

City/Highway

Composite

26 mpg (9.05 L/100km)

US06

24.6 mpg (9.55 L/100km)

“Fleet” results are based on simulations of 227 vehicle 

driving profiles from St. Louis metropolitan area.
14

0 5 10 15 20 25 30 0

5

10152025303540

Time of Day (hr)

Percentage of Vehicle Fleet In Use (%)

0 5 10 15 20 25 300

50100150200250300350400

Cumulative Fuel Consumed (gallons)

ConventionalHybridPHEV20PHEV40

PHEVs Reduce Fuel Consum

On Real-World 

• 8647 total miles driven• 100% replacement of 

sample fleet

227 vehicles from St. Louis each 227 vehicles from St. Louis each modeled as a convention

modeled as a convention

26 mpg

58 mpg & 

140 Wh/mi

37 mpg

76 mpg & 

211 Wh/mi
15

Simulated In-Use All-Electric Ran

• Vehicles were designed to operate all 

on UDDS

• Power demands of real profiles exceed 

power within the first few miles

1 3 5 7 9 11 13 15 17 19 21 23 25

05

1015202530

All Electric Range (mi)

Percentage of Fleet (%)

PHEV20

0 5 10 1

05

10152025303540

A

Percentage of Fleet (%)
16

Fuel Economy and All-Electric Rang

• Significant difference between rated 

cycles) and real-world median value

— Consumers likely to observe fuel eco

than rated value in daily driving

— Vehicles designed with all-electric ra

operate in a blended mode to meet d

** Fuel economy values do not include electrical energy 

Rated Median Rated 

Conventional 26 24.4 n/a 

HEV 39.2 35.8 n/a PHEV20 54 70.2 22.3 PHEV40 67.4 133.6 35.8 

Fuel Economy (mpg) ** All Elec
17

PHEV20 Savings Relative to Conven

• Savings relative to 

conventional are almost entirely distance dependent

• Savings relative to 

HEV are distance dependent up to PHEV distance then constant 
18

Insights:

The PHEV20s that saved the most fuel relative to an HEV travel under 60 mph and light accelerationsThe PHEV20s that saved the least fuel relative to the HEV in the 

periods of 60+ mph highway driving and the accelerations were s

aggressive 

Most Savings L

Deep Dive into Real-World PHEV 
19

Summary and C

• PHEVs provide petroleum displacement th

flexibility

• Design needs to consider a spectrum of s

objectives

• Analysis of real-world travel behavior prov

perspective on design challenges

— Vehicles designed as all-electric likely to ope— What’s emissions impact of real-world blend

• In-use petroleum displacement not tied to 

range

— Consider energy equivalent all-electric range

• PHEV benefit is strongly related to distanc

aggressiveness of real-world usage