Plug-In HEV Vehicle Design Options and Expectations
ZEV Technology Symposium California Air Resources Board Sacramento, CA
September 27, 2006
Tony Markel National 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 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
2 PHEV Stakeholder Objectives
Consumers US Gov./DOE Affordable California Gov. Reduced petroleum use Fun to drive Reduced air pollution Functional
Auto Manufacturer Electric Utility Sell cars Sell electricity
3 A Plug-In Hybrid-Electric Vehicle (PHEV)
Fuel Flexibility BATTERY RECHARGE
REGENERATIVE BRAKING
PETROLEUM
AND/OR
ELECTRICITY ELECTRIC ACCESSORIES
ADVANCED ENGINE ENGINE IDLE-OFF
ENGINE DOWNSIZING 4 Some PHEV Definitions
Charge-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 5 Battery Definition as Key Input to Simulation
Input parameters that define the battery in BLUE
mass compounding Benefit of PHEV range plugging-in
kWh/mi kWh usable (from simulation)
SOC window kWh total Total MPG Benefit
P/E ratio kWmotor Benefit of DOH Performance hybridization constraints kWengine
DOH = degree of hybridization 6 Batteries in Current PHEVs NiMH
Varta Electro Energy Inc. Li-Ion Co/Ni based Johnson Controls/SAFT Kokam
Valence Technology based Li-Ion A123 Systems 7 Iron phosphate Battery SOC Design Window
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 kWh kWh = useable factor in battery sizing: total SOC window
Battery SOC swing is a strong Battery cycle life is a strong function of driving habits: function of SOC swing:
Daily Mileage Probability Distribution
25%
20%
15%
10% Probability (%)
5%
0% 0 102030405060708090100 Daily mileage (<= mi)
8 Battery SOC Design Window
Battery SOC design curve for 15 year cycle life 100%
90%
80%
70% Average daily SOC swing based on daily 60% Design SOC window mileage distribution based on PHEVx 50%
40%
30%
20%
10% Daily mileage probability distribution 0% 0 102030405060 Daily Mileage / PHEV x
9 Operating Strategy Options All-Electric or Blended All-Electric 70 100% 90% 60 engine • Engine turns on when battery motor 80% 50 SOC reaches low state of charge 40 70% • Requires high power battery and 30 60% motor 20 50%
10 40% (%) SOC Power (kW) 0 30%
-10 20% 70 Blended 100% -20 10% 90% 60 engine 0 5 10 15 20 25 30 35 40 motor -30 0% 80% Distance (mi) 50 SOC
40 70%
30 60%
20 50%
• Engine turns on when power 10 40% (%) SOC Power (kW) exceeds battery power capability 0 30% • Engine only provides load that -10 20% exceeds battery power capability -20 10% -30 0 5 10 15 20 25 30 35 40 0% Distance (mi)
10 Real Driving Survey Data • Provides valuable insight into travel behavior • GPS augmented surveys supply details needed for vehicle simulation
11 St. Louis Travel Data Analysis Daily Driving Distance Similar to 1995 NPTS Data
St. Louis HHTS Data 1995 NPTS Data 7 100 12 100
90 90 6 10 80 80
5 70 70 Frequency (%) 8 Cumulative Freq. (%) 60 60 4 50 6 50 3 40 40 Frequency (%) Frequency
Frequency (%) 4 30 2 30 20 Cumulative Frequency (%)
20 2 Cummulative Frequency (%) 1 10 ~29 mi 10 ~33 mi 0 0
0 0 5 0 0 5 0 15 20 2 3 45 50 55 70 75 8 8 95 2 4 6 8 0 2 6 8 0 2 4 6 0 2 4 6 8 0 4 6 8 0 0-5 -10 - - - 100 1 1 14 16 18 20 22 24 2 2 3 32 34 36 38 40 4 4 4 48 50 52 54 56 58 6 6 6 66 68 70 72 74 7 7 8 82 84 86 88 90 92 9 9 9 5 5- 0- 5- 0- 0- - 10 10 1 20- 25- 30-3535-404 4 5 55-6060-6565 7 75- 80- 85-9090 Daily Travel Distance (miles) 95 Daily Distance (mi)
• 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
12 Consumption Distribution Many PHEVs Better than Rated Values Conventional Hybrid 40 40 City/Highway Composite 30 City/Highway 30 39.2 mpg (6.0 L/100km) Composite 26 mpg (9.05 L/100km) US06 33.2 mpg (7.1 L/100km) 20 US06 20 24.6 mpg (9.55 L/100km) Real-world 10 Real-world 10 Percentage of Fleet (%) Fleet of Percentage (%) Fleet of Percentage 0 0 0 5 10 15 20 25 0 5 10 15 20 25 Fuel Consumption (L/100km) Fuel Consumption (L/100km) PHEV20 PHEV40 40 40 City/Highway City/Highway Composite Composite 54 mpg (4.35 L/100km) 30 30 67.4 mpg (3.49 L/100km)
US06 US06 20 39.6 mpg (5.94 L/100km) 20 51.5 mpg (4.57 L/100km)
Real-world Real-world 10 10 Percentage of Fleet (%) Fleet of Percentage (%) Fleet of Percentage 0 0 0 5 10 15 20 25 0 5 10 15 20 25 Fuel Consumption (L/100km) Fuel Consumption (L/100km)
13 “Fleet” results are based on simulations of 227 vehicle driving profiles from St. Louis metropolitan area. PHEVs Reduce Fuel Consumption By >50% On Real-World Driving Cycles
227 vehicles from St. Louis each modeled as a conventional, hybrid and PHEV
40 400 Conventional Average Daily Costs Hybrid 26 mpg 35 350 Gas. Elec. ¢/mi PHEV20 PHEV40 CV $3.45 --- 9.1 30 300 HEV $2.48 --- 6.5 37 mpg 25 • 8647 total miles driven 250 PHEV20 $1.58 $0.48 5.4 • 100% replacement of sample fleet PHEV40 $1.21 $0.72 5.1 20 58 mpg & 200 140 Wh/mi Assumes $2.41/gal and 9¢/kWh 15 150
10 100 PHEVs: 76 mpg & >40% reduction in energy costs 5 211 Wh/mi 50 Cumulative Fuel Consumed (gallons) Consumed Fuel Cumulative Percentage of Vehicle Fleet In Use (%) Use In Fleet of Vehicle Percentage >$500 annual savings
0 0 0 5 10 15 20 25 30 Time of Day (hr)
14 Simulated In-Use All-Electric Range Distribution
PHEV20 PHEV40 30 40
35 25
30
20 25
15 20
15 10 Percentage of Fleet (%) Percentage of Fleet (%) 10
5 5
0 0 1 3 5 7 9 11 13 15 17 19 21 23 25 0 5 10 15 20 25 30 35 40 All Electric Range (mi) All Electric Range (mi)
• Vehicles were designed to operate all electrically on UDDS • Power demands of real profiles exceed UDDS peak power within the first few miles
15 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 (mpg) ** All Electric Range (mi) Rated Median Rated Median Conventional 26 24.4 n/a n/a HEV 39.2 35.8 n/a n/a PHEV20 54 70.2 22.3 5.6 PHEV40 67.4 133.6 35.8 3.8 ** Fuel economy values do not include electrical energy consumption
16 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
17 Deep Dive into Real-World PHEV Simulations
Most Savings Least Savings
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 18 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
19