Midsize and SUV Vehicle Simulation Results for Plug-In HEV Component Requirements 2007-01-0295

2007-01-0295
Midsize and SUV Vehicle Simulation Results for
Plug-In HEV Component Requirements
Phillip Sharer, Aymeric Rousseau, Sylvain Pagerit, Paul Nelson
Argonne National Laboratory
Copyright © 2007 SAE International
ABSTRACT
Because Plug-in Hybrid Electric Vehicles (PHEVs)
substitute electrical power from the utility grid for fuel,
they have the potential to reduce petroleum use
significantly. However, adoption of PHEVs has been
hindered by expensive, low-energy batteries. Recent
improvements in Li-ion batteries and hybrid control have
addressed battery-related issues and have brought
PHEVs within reach. The FreedomCAR Office of Vehicle
Technology has a program that studies the potential
benefit of PHEVs. This program also attempts to clarify
and refine the requirements for PHEV components.
Because the battery appears to be the main technical
barrier, both from a performance and cost perspective,
the main efforts have been focused on that component.
Working with FreedomCAR energy storage and vehicle
experts, Argonne National Laboratory (Argonne)
researchers have developed a process to define the
requirements of energy storage systems for plug-in
applications. This paper describes the impact of All
Electric Range (AER), drive cycle, and control strategy
on battery requirements for both the midsize and SUV
classes of vehicles.
INTRODUCTION
Relatively detailed comparisons between plug-in hybrid
powertrains and hybrid powertrains were recently
completed [1]. However, these studies did not examine
the potential benefit of using a Li-ion battery. To evaluate
the battery requirements for different Plug-in Hybrid
Electric Vehicle (PHEV) options, Argonne’s vehicle
simulation tool, Powertrain System Analysis Toolkit
(PSAT), was used with a battery model designed by
Argonne’s battery research group.
In this study, we describe the component models and
control strategies developed to characterize PHEVs for
both midsize and SUV classes of vehicles. The impact of
All Electric Range (AER) on fuel efficiency will be
analyzed to provide direction on the most appropriate
sizing strategy. Then, the main battery parameters,
including energy, power, current and voltage, will be
evaluated. AER is defined, in this paper, as the distance
that the vehicle can travel by only using energy from the
battery while repeating the Urban Dynamometer Driving
Schedule (UDDS). The last UDDS is always truncated.
AER considered a range from 7.5 to 60 mi.
PSAT VEHICLE MODELING
PSAT [2, 3], developed with MATLAB and Simulink, is a
vehicle-modeling package used to estimate performance
and fuel economy. PSAT is the primary vehicle
simulation package used to support the U.S. Department
of Energy (DOE) FreedomCAR R&D activities. In PSAT,
a driver model estimates the wheel torque that the
vehicle needs to follow a predetermined speed trace.
Using the driver model’s estimate of wheel torque, the
vehicle controller calculates a command for each
component in the powertrain, such as throttle position for
the engine, displacement for the clutch, gear selection
for the transmission, or mechanical braking for the
wheels. Because components in PSAT are commanded,
real control strategies can be used along with advanced
component models, which predict component behavior
during transient events (e.g., engine starting, clutch
engagement/disengagement, or shifting). Finally, test
data measured at Argonne’s Advanced Powertrain
Research Facility have been used to quantify the
accuracy of PSAT vehicle models.
VEHICLE DEFINITION
Vehicles representative of the midsize and SUV classes
were sized to meet the performance criteria in Table 1.
For each vehicle class, five types of powertrains were
simulated: conventional, mild parallel hybrid, full parallel
hybrid, fuel cell vehicle, and fuel cell hybrid vehicle.
Table 2 shows the common characteristics of the
midsize vehicles, and Table 3 shows the common
characteristics of the SUVs.
Table 1. Performance Requirements
Parameter
0–60 mph
0–30 mph
Grade at 55 mph
Maximum Speed
Unit
s
s
%
mph
Value
9 +/- 0.1
3
6
> 100
Table 2. Main Specifications of the Midsize Vehicle
Component
Engine
Electric machine
Battery
Transmission
Frontal Area
Final Drive Ratio
Drag Coefficient
Rolling Resist.
Wheel radius
Specifications
Gasoline based on LK5 data
UQM SR218N
Li-ion – VL41M
5-speed manual Ratios:
[3.42, 2.14, 1.45, 1.03, 0.77]
2
2.244 m
3.8
0.315
0.008 (plus speed-related term)
0.3175 m
Table 3. Main Specifications for the Sport Utility Vehicle
Component
Engine
Electric machine
Battery
Transmission
Frontal Area
Final Drive Ratio
Drag Coefficient
Rolling Resist.
Wheel radius
Specifications
Gasoline based on LK5 data
UQM SR218N
Li-ion – VL41M
5-speed manual Ratio: [3.42, 2.14,
1.45, 1.03, 0.77]
2
2.46 m
3.83
0.41
0.0084 (plus speed-related term)
0.368 m
As shown in Figure 1, the configuration selected is a pretransmission parallel hybrid, similar to the one used in
the DaimlerChrysler Sprinter Van [1].
BATTERY
In this study, equations were derived for calculating the
impedance of a plug-in hybrid vehicle battery for use in
simulating the battery behavior under driving conditions.
Developing the equations for expressing battery
resistance for a plug-in hybrid vehicle battery is more
complex than developing those for a standard hybrid
vehicle because the plug-in battery may be charged and
discharged during vehicle operation for periods lasting
several minutes. Ideally, the equations should be able to
reproduce the measured voltage curves for a complete
discharge and charge at constant current, as well as the
battery resistance under conditions of rapidly changing
currents. Current and voltage data taken at Argonne
were available for a cell fabricated by SAFT, Inc., which
is somewhat similar to its 41-A•h lithium-ion cell
(designated VL 41M, as listed on SAFT’s web site). The
VL41M cell has a capacity of 41- A•h at the 3-h rate and
a power of 1,000 W (400 A at 2.5V) at 80% Depth of
Discharge (DOD). The data for the cell measured at
Argonne were for a 3-h discharge at constant current
and for Hybrid Pulse Power Characterization (HPPC)
tests [4]. These data were fit to an electronic simulation
model with two time constants (Figure 2) of the form:
( OCV − VL )
IL
=R0 + R p1 ×
dt
This study accounts for uncertainty in component
specifications by considering two cases: a slow
technology advancement case and a fast technology
advancement case. Fast technology advancement
represents the consequences of achieving the
FreedomCAR
goals,
while
slow
technology
advancement represents the consequences of achieving
more conservative improvements. Specifically, these
cases are used to capture the uncertainty in the
improvement in the efficiency and specific power of the
engine and electric motor.
IL
+ Rp2 ×
I p2
IL
(1)
In this relationship, OCV and VL are the open circuit and
load voltages; Ro, Rp1, and Rp2 are the ohmic
resistance and the polarization impedances; and Ip1/IL
and Ip2/IL are the ratios of the polarization currents to
the load current. The polarization currents are
determined by integration of the equation:
dI p
Figure 1. Configuration Selected – Pre-Transmission
Parallel HEV
I p1
=
(I L − I p )
τ
(2)
for each of the polarization impedances (where τ1 and
τ2 are time constants of 22.8 and 270 s, respectively), as
in an earlier study that also used two polarization
impedances [5] and in the PNGV Lumped Parameter
Model [6] of the DOE, which was a similar model with
one polarization impedance. The parameters in the
equation (OCV, Ro, Rp1, Rp2) were selected to match
the measured data for both the 3-h discharge and the
HPPC data for the entire range of the discharge, and
these parameters were presented in the form of a lookup
table with values from 0% to 100% state of charge
(SOC) at 10% intervals (τ1 and τ2 were held constant
over the entire discharge). These results were converted
to a similar table for the SAFT 41- A•h cell, VL41M, by
using a multiplying factor that matched the calculated
impedance at 80% DOD with that given for the VL41M
cell.
Vehicle Assumptions
IL
Ro
Motor Power for UDDS
OCV
VL
Battery Power
Rp1
Rp2
Engine Power
Ip1
Ip2
Figure 2. Battery Electric Circuit Model
The utility of the model was further extended to include
cells of the same chemistry, but with capacities in the
range of 10–100 A•h and capacity-to-power ratios (C/P)
of 0.75–3.0 times that of the VL41M cell and for batteries
containing any number of such cells. This was done by
developing a set of equations used to determine the
multiplying factor for converting the lookup table
developed for the parameters of the VL41M cell to the
appropriate values for the desired cell capacity and
power. For instance, some of the equations (with
compatible dimensions) are shown here:
(C/P)41 = ratio of capacity to power at 80% DOD and
2.5 V for VL41M cell
CC = capacity of simulated battery cell
FC = capacity factor for cell = (C/P)C/(C/P)41
M = number of 6-cell modules in battery
N = number of cells in battery = 6 × M
R41 = resistance of VL41 M cell = Ro+Rp1 ×
Ip1/IL+Rp2 × Ip2/IL
RB = resistance of battery = R41 × FC × (41/CC) × N
PB = power of battery at = P41/FC × CC/41 × N
COMPONENT SIZING PROCESS
To quickly size the component models of the powertrain,
an automated sizing process was developed. A flow
chart illustrating the logic of the sizing process is shown
in Figure 3. While the engine power is the only variable
for conventional vehicles, HEVs have two variables:
engine power and electric machine power. PHEVs add a
third degree of freedom: battery energy. The sizing
process defines the peak mechanical power of the
electric machine as being equal to the peak power
needed to follow the UDDS while in all-electrical mode.
The peak discharge power of the battery is then defined
as the electrical power that the motor requires to
produce its peak mechanical power. The sizing process
then calculates the peak power of the engine by using
the power of the drivetrain required to achieve the
gradeability requirement of the vehicle.
The 0–60-mph performance requirement for the vehicle
is satisfied implicitly by the constraints on the peak motor
power and the peak engine power. The power required
Battery Energy
Oversize Battery
No
Convergence
Yes
Figure 3. Vehicle Component Sizing Process
by the motor for the vehicle to follow the UDDS cycle
added to the power required by the engine for the
vehicle to drive up a 6% grade at 55 mph exceeds the
power the vehicle needs to go from 0 to 60 mph in 9 s.
Finally, the battery energy is sized to achieve the
required AER of the vehicle. The AER is defined as the
distance the vehicle can travel on the UDDS without
starting the engine. Note that a separate control
algorithm is used to simulate the AER. This algorithm
forces the engine to remain off throughout the cycle,
regardless of the torque request from the driver. Two
constraints were imposed on the battery: bus voltage
and cell capacity. The sizing algorithm maintained the
bus voltage at 200 V until the cell capacity equaled
90 A•h. The sizing algorithm then added energy to the
battery pack by adding additional cells rather than by
increasing the cell capacity. Thus, for these battery
sizes, the bus voltage was allowed to exceed 200 V. For
safety reasons, it was assumed that the cell capacity
should not exceed 90 A•h.
Finally, the battery power is oversized by 30% and its
energy by 20% to account for battery aging over the life
of the vehicle. This assumption will be modified once
more battery data become available. When motor power,
engine power, and battery energy are changed, the
vehicle mass is recomputed. Using these new values,
the algorithm checks the vehicle against the
performance criteria. If the criteria are met, the vehicle is
defined and the algorithm exits. If the criteria are not
met, the algorithm executes another iteration, adjusting
the motor power, the engine power, and the battery
energy, again. It then rechecks the criteria. The
algorithm continues to loop until it converges within the
+/-0.1-second tolerance on the performance criteria
specified in Table 1. The algorithm searches for the
vehicle mass that solves equation 3:
δm
+
Peng ( M veh )
δ eng
+ N cell (1.3Pbatt ,1.2 Ebatt ) × ...
Charge Sustaining (CS)
90
(3)
M cell (1.3Pbatt ,1.2 Ebatt ) + M glider =
M veh
SOC (%)
Pm ( M veh )
Charge Depleting (CD)
30
For which Pm is the motor peak power, Peng is the engine
peak power, Pbatt is the battery peak power, Ebatt is the
battery total energy capacity, M veh is the vehicle total
mass, M glider is the mass of the vehicle’s glider, M cell is
the mass of a battery cell, δ m is the specific power of the
motor, δ eng is the specific power for the engine,
and N cell is the number of cells connected in series to
form the battery pack.
Seven AER values (7.5, 10, 20, 30, 40, 50, and 60 mi)
were simulated. Figure 4 shows three ranges that were
defined for each vehicle. The end-of-life (EOL) AER
confirms the validity of the sizing algorithm. One notices
that an additional AER is available at the beginning of
life (BOL).
Excess energy is added to maintain a consistent range
throughout the life of the vehicle. At the beginning of life,
the control strategy would limit the vehicle range to the
value it has at the end of its life, and the additional
energy of the battery would not be used. As the battery
ages, it loses this excess energy until at the EOL it has
enough energy just to meet the range requirement.
Thus, the user of the vehicle would never experience a
gradual loss in vehicle AER.
CONTROL STRATEGY
The control strategy can be separated into two distinct
modes, as shown in Figure 4:
Distance
Figure 4. Control Strategy SOC Behavior
Initial state-of-charge (SOC) of the battery, which is also
the battery’s maximum charge, is 90%, and the final
SOC of the battery, which is also the battery’s minimum
charge, is 30%. For the CD mode, the engine logic was
written in StateFlow and used several conditions, such
as battery SOC, motor power limits, and vehicle speed,
to determine when the engine should turn on and the
output torque of the engine. The logic of the CS mode
was similar to that of current HEVs.
The primary goal of the study is to define the component
requirements — the CD control strategy has been used
as it represents the most demanding scenario.
Moreover, because the battery was sized to follow the
UDDS driving cycle, the engine is not used during the
CD mode.
VEHICLE LEVEL RESULTS
As expected, since the powertrain configurations were
identical and the control was similar, the trends for the
midsize vehicle and the SUV were the same as shown in
Figure 5. As EOL all-electric range was increased from
7.5 to 60 mi, the midsize vehicle gained 250 kg and the
SUV gained 320 kg. This gain was due almost entirely to
the increase in size of the battery pack. As distance is
increased, pack mass is increased. Since both the
2400
•
Charge-Depleting (CD): Vehicle operation on the
electric drive, engine subsystem, or both with a net
decrease in battery state-of-charge.
Charge-Sustaining (CS): Vehicle operation on the
electric drive, engine subsystem, or both with a
“constant” battery state-of-charge (i.e., within a
narrow range), which is similar to that in current
production HEVs.
During a simulation, the engine is turned on when the
driver torque request is sufficient. Turning the engine on
expends fuel but conserves battery energy, so that more
miles can be traveled before the battery reaches its
discharged state.
2300
2200
Vehicle Mass (kg)
•
~320
2100
2000
1900
1800
~250
1700
SUV
Midsize
1600
1500
7.5
10
20
30
40
50
60
End of Life All Electric Range (miles)
Figure 5. Small Vehicle Mass Increase from 7.5 to 60 mi All
Electric Range
midsize vehicle and the SUV used Li-ion battery packs,
the increase was nearly linear, from 7.5 to 60 mi.
Ess Mass / Vehicle Mass
18
Figure 6 shows the increase in battery pack mass for
each vehicle class. Because of the high specific power
of the Li-ion technology (ranging from 1,400 W/kg to
370 W/kg, depending on the capacity), the battery pack
is relatively light, especially when compared to other
battery chemistries (such as NiMH). For the midsize
vehicle, the increase in battery mass between a vehicle
that has an AER of 7.5 mi and one of 60 mi is only
220 kg for the SUV, and the battery pack is only 80 kg
heavier. An additional increase in each vehicle’s mass
results from an increase in the power of the engine and
electric motor. As the vehicle gets heavier, as a result of
the larger battery pack (which is sized to meet the longer
range requirement), the engine peak power is increased
so that the heavier vehicle can satisfy the gradeability
requirement. Similarly, the motor peak power is
increased in order for the vehicle to meet the all-electric
city driving constraint. Thus, although the battery pack is
the greatest contributor to the increase in mass,
increases in the mass of the engine and electric motor
also occur.
450
SUV
Midsize
400
SUV
Midsize
14
12
10
8
6
4
2
0
7.5
500
150
100
50
0
7.5
10
20
30
40
50
60
40
50
60
SUV
Midsize
450
~220 kg
30
The electric consumption during the CD operating mode
on a UDDS cycle is nearly constant for both vehicle
classes. While operating in CD mode, the battery and
electric motor propel the vehicle. A high powertrain
efficiency implies that the vehicle has an energy
consumption with a low sensitivity to changes in vehicle
mass [6]. Thus, the increase in vehicle mass of 16%
results in a relatively small increase in energy
consumption, as shown in Figure 8.
~300 kg
200
20
Figure 7. Share of Battery Mass Increases but Midsize and
SUVs are Comparable
300
250
10
End of Life All Electric Range (miles)
Energy Consumption (Wh/mile)
Battery Pack Mass (kg)
350
Percentage of Battery Mass
16
400
350
300
250
200
150
100
End of Life All Electric Range (miles)
50
Figure 6. Li-Ion High Specific Power Leads to a Small
Mass increase
0
7.5
10
20
30
40
50
60
End of Life All Electric Range (miles)
The Li-ion battery pack for both the midsize vehicle and
the SUV is a small fraction of the total mass of the
vehicle, compared to NiMH chemistries. Referring to
Figure 7, for the shortest range PHEV of 7.5 mi, the
battery pack is less than 4% of the total vehicle mass.
Even for the 60-mi range, the battery pack constitutes
only 16% of the total mass of the vehicle. The difference
between these percentages for the midsize vehicle and
SUV is about 1%. Because the powertrain architecture,
the control strategy, and the battery technology are
similar, so are the trends.
Figure 8. Electrical Consumption Remains Almost
Constant
Because the electric consumption is constant regardless
of the range that PHEV was designed to travel in the
CD mode, the total electrical consumption for this
operating mode is a linear function of the CD range, as
shown in Figure 9.
18
30000
26489
SUV
Midsize
SUV
Midsize
16
14
22009
12
20000
17261
W/Wh
Energy Consumption (Wh)
25000
16578
15000
12686
10
8
13591
10739
8550
10000
6
7956
4191
5000
4
5228
3220
2
2549
1936
0
0
0
10
20
30
40
50
60
10
70
20
30
40
50
End of Life All Electric Range (miles)
End of Life All Electric Range (miles)
Figure 11. SUV Requires Lower Power-to-Energy Ratio
Figure 9. Energy Consumption
Figure 10 shows the battery peak power required for
each vehicle at EOL. The SUV consistently requires
20% more power than the midsize vehicle. The values
represent the 2-second power pulses necessary to
follow the UDDS driving cycle in all-electric mode.
70
SUV
Midsize
Energy Storage Power (kW)
60
Figure 12 shows the cell capacity for each battery pack.
To travel the desired range, battery pack energy can be
added either by adding more cells or by increasing the
charge capacity of each cell. The sizing algorithm, which
was used for this study, fixed the battery voltage to
200 volts, which is representative of the bus voltage in
production hybrids. There are several drawbacks to
having a high bus voltage:
•
50
40
•
30
•
20
10
10
20
30
40
50
60
End of Life All Electric Range (miles)
Figure 10. EOL Battery Peak Power (2-s Pulse)
Because battery peak discharge power remains virtually
constant as the PHEV range is increased and the battery
energy increases linearly with PHEV range, the powerto-energy ratio of the battery varies hyperbolically with
range, as Figure 11 shows. The x-axis in Figure 11 is to
scale between 10 and 60 mi; however, between 7.5 and
10 mi the axis is dilated, so that the 7.5-mi bar does not
appear to fall on the sketched hyperbola.
Figure 11 also shows that for each range, the SUV
battery requires a lower power-to-energy ratio than the
midsize vehicle. This result agrees with Figure 8, which
shows energy consumption, and Figure 10, which shows
peak battery power. The SUV peak battery power is 20%
greater than that of the midsize vehicle, while the energy
consumption is 40% greater.
Increasing the cell voltage requires additional cells in
series, which increases the complexity of the battery
pack.
The motor-inverter power electronics have to handle
a higher bus voltage.
The inverter also has to handle a larger swing in bus
voltage as the PHEV discharges its battery pack.
As large cell capacity also has disadvantages, the sizing
algorithm fixes the maximum capacity of a cell to 90 A•h.
Once 90 A•h is reached, energy is increased by adding
more cells.
100
SUV
Midsize
90
80
Cell Capacity (Ah)
0
7.5
60
70
60
50
40
30
20
10
0
7.5
10
20
30
40
End of Life All Electric Range (miles)
Figure 12. Cell Capacity Is Saturated at 90 A•h
50
60
As shown in Figure 13, by adding additional capacity to
the battery, the bus voltage can be fixed at 200 V up to
the 30-mi range. For this range, the capacity of a cell is
at its maximum; thus, additional energy is added to the
pack by increasing the number of cells. One can see in
the figure that the bus voltage reaches 600 V.
The current distributions for each 40-mi PHEV, shown in
Figure 15, show that the current supplied in both cases
is nearly identical. This is expected. The additional
energy and power for the SUV is provided in the form of
voltage rather than in the form of current. This is a
further consequence of adding energy with cells as
opposed to adding energy with capacity.
700
SUV
Midsize
Energy Storage Current
10
SUV
Midsize
9
500
8
7
400
Percent
Battery Pack - Nominal Voltage (V)
600
300
6
5
4
200
3
100
2
1
0
7.5
10
20
30
40
50
60
End of Life All Electric Range (miles)
Figure 13. Bus Voltage Is Maintained up to 30-mi Range
Because the SUV requires more energy to satisfy the
40-mi range requirement and because the maximum cell
capacity is saturated at 90 A•h for both vehicle classes,
the SUV bus operates at a higher average voltage,
which is shown in the histogram in Figure 14. The
histogram for the midsize PHEV with a 40-mi range is on
the left, and the histogram for the SUV PHEV with a
40-mi range is on the right. These histograms also show
that the SUV voltage bus experiences a wider swing in
voltage than the midsize vehicle, which is expected,
because the SOC varies from 90% to 30% for each
battery.
0
-100
-50
0
50
100
Current (amps)
150
Figure 15. Histogram of Current for 40-mi PHEVs –
Fast Technology Case
The amount of energy recovered during regenerative
braking is also an important consideration for PHEVs. As
mentioned previously, the main goal of the study is to
define the component requirements on the basis of
worst-case scenarios. Consequently, the US06 driving
cycle was selected to define the battery charging power
requirements during deceleration. Figure 16 shows the
histogram for battery power during regenerative braking
on a US06 cycle. The histogram indicates that the
maximum power necessary for regenerative braking on
a US06 cycle is 35 kW.
Energy Storage Voltage
SUV
Midsize
6
5
Percent
4
3
2
1
0
260
280
300
340
320
Voltage (volt)
360
380
Figure 14. Histogram of Bus Voltage for 40-mi PHEVs
– Fast Technology Case
200
Figure 16. Histogram of Battery Power during
Regenerative Braking on US06 Cycle for Midsize
40-mi PHEV – Fast Technology Case
ELECTRIC MACHINE REQUIREMENTS
Because the mass increase is not significant from the
7.5-mi range to the 60-mi range PHEV, the peak power
needed to propel each type of PHEV is not significant.
Thus, the power of each drivetrain component remains
essentially constant. Figure 10 demonstrates this
phenomenon for the battery, and Figure 17
demonstrates this phenomenon for the electric motor. In
Figure 17, the FreedomCar goal for the electric machine
is shown. Achieving the FreedomCar goal of 55 kW
would produce a motor capable of handling all of power
requirements of the midsize PHEVs shown in Figure 17;
however, this goal would only meet the power
requirements for the SUVs up to 30 mi AER.
Few points > 35 kW
Peak Electric Machine Power (kW)
65
60
SUV
Midsize
FreedomCAR Target
Figure 18. Motor Power for SUV PHEV 40-mi Range – Fast
Technology Case
55
Figure 19 shows that the midsize PHEV only needs a
motor with a peak power of 25 kW to satisfy 90% of its
power demand.
50
45
40
35
30
7.5
10
20
30
40
50
60
End of Life All Electric Range (miles)
Figure 17. Electric Machine Power Remains Almost
Constant
Although more than 55 kW is necessary to meet the
peak power demand for the 40-mi SUV PHEV, Figure 18
demonstrates that this power is rarely required for the
SUV on the UDDS. Most of power requests to the motor
are below 35 kW. Thus, the FreedomCAR goal of 55 kW
would satisfy 90% of the SUV 40-mi PHEV power
requirements during its CD operation. If the current
electric machine peak power requirements were
maintained, the engine could be turned on to satisfy the
demand.
Also note that, where the peak battery and electric
machine powers have been defined to follow the UDDS,
lower power requirements could still lead to significant
fuel displacements and lower component costs.
Few points >
25 kW
Figure 19. Motor Power for Midsize PHEV 40 mi Range –
Fast Technology Case
As range increases, battery mass is added to the
vehicle. Because this mass contributes around a 20%
increase in total vehicle mass, the component maximum
power
does
not
change
radically. Figure 20
demonstrates that between a 7.5-mi range and a 60-mi
range, the engine power increases by roughly 10%.
130
battery and electric machine powers. To do so, we
analyzed the impact of using the current battery
requirements for power-assist HEV. Table 4 summarizes
the results of these simulations.
SUV
Midsize
120
Engine Power (kW)
110
100
Because the battery power available is not sufficient to
follow the UDDS using only the electrical power, a
Charge-Depleting Range (CDR) was considered instead
of an AER. In that case, because we still want to define
the worst-case scenario for the battery, the engine is
only started when the power requested by the driver
cannot be provided by the battery alone. Once the
engine is ON, it is used close to its best efficiency curve,
and it consequently may recharge the battery in specific
instances.
90
80
70
60
50
40
7.5
10
20
30
40
50
60
End of Life All Electric Range (miles)
Figure 20. Engine Power Increases with Vehicle Mass
The consequence is a decrease of the total energy
required by the battery from 5.2 to 4.7 kWh for a 20-mi
distance.
BATTERY SIZING IMPACT ON REQUIREMENTS
Because a main issue with PHEVs is their additional
costs, we considered the possibility of reducing the
This approach, while still displacing significant amount of
fuels, has the advantage of lowering the requirements
and consequently the cost of the components.
Table 4. Impact of Battery Peak Power on Energy Requirements
Characteristics
Pulse Discharge Power (2 sec)
Pulse Discharge Power (10 sec)
Max Regen Pulse (2 sec) - USO6
Max Regen Pulse (10 sec)
Total Available Energy
Units
HEV
(Midsize)
kW
kW
kW
kW
kWh
CONCLUSION
Component models and control strategies have been
developed and implemented in PSAT to study the impact
of AER, drive cycle, control strategy, and component
sizing on the battery requirements. The following
conclusions can be stated:
•
•
•
•
•
The midsize and SUV classes of vehicles exhibit
similar energy consumption trends during CD mode.
As would be expected, of the two, the SUV has the
greater overall energy and power needs.
The battery energy is approximately a linear function
of the AER.
Power requirements are not significantly influenced
by the AER as a result of the high specific energy of
the Li-Ion battery.
The high specific power of Li-ion technologies does
not have a significant influence on vehicle mass.
Specific energy has the greatest affect on vehicle
mass.
Battery pack voltage needs to be taken into
consideration for high AER (above 40 mi). Higher
capacities or battery packs in parallel might need to
be used.
20 Mile Range
40 Mile Range
AER
AER
CDR
44
25
46
25
32
20
0.3
5.2
CDR
25
34
20
4.7
10.7
20
5.2
The results of these simulations will be used to define
the component requirements of PHEV vehicles
implemented in the U.S. DOE R&D plan.
ACKNOWLEDGMENTS
This work was supported by the U.S. Department of
Energy, under contract DE-AC-02-06CH11357. The
authors would like to thank Lee Slezak, Dave Howell,
and Tien Duong from U.S. DOE for their support and
guidance.
CONTACT
Phillip Sharer, Research Engineer, Argonne National
Laboratory, 9700 South Cass Avenue, Argonne, IL
60439-4815, USA, psharer@anl.gov
Aymeric Rousseau, Research Engineer, Argonne
National Laboratory, 9700 South Cass Avenue,
Argonne, IL 60439-4815, USA, arousseau@anl.gov
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the
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