EC Power
341 N. Science Park Rd.
State College, PA, 16803, USA
[email protected]
Ph: +1-814-861-6233
Reduction of EV Drive Range at Cold Temperatures
The substantial drop in EV driving range at cold
winter temperatures has been well documented and
widely reported [1,2]. One recent AAA study tested
three
EVs
undergoing
climate
controlled
dynamometer testing, and reported that under urban
stop and go driving, the average range at 75oF (24oC)
was 105 miles, but dropped to only 43 miles at 20 oF
(-7oC), a reduction of 57%. In this case study, we
demonstrate how the temperature-dependent range of
an EV can be predicted in the vehicle design phase
through the use of AutoLion-ST™. Specifically, we
develop a model for a typical EV100 (100 mile EV)
that includes drag, braking, drivetrain inefficiencies,
and propulsion/regeneration from the electric motor,
along with a battery pack powered heat pump that is
turned on for ambient temperatures of 10oC and
below. Within Simulink, we couple these models to
AutoLion-ST™, and use repeated cycling of the
Urban Dynamometer Driving Schedule (UDDS) to
drive the vehicle and investigate the vehicle range
limitations at various temperatures.
Software Used
 AutoLion-STTM
Setup
 A 24 kWh 96s/2p battery pack was developed in
AutoLion-ST™. 33 Ah prismatic cells of 70/30
LMO/NMC blended cathode and graphite anode
were used. The battery pack and cells were
loosely designed based on the first generation
Nissan Leaf. The C/3 discharge of the designed
cell is given in figure 1.
 A vehicle sub-model was developed in
Simulink based on Newton’s Second Law, and
includes drag, braking, drivetrain inefficiencies,
and propulsion/regeneration from the electric
motor. Typical values of drag coefficient, etc.
for an EV100 were used, and it was assumed
that 35% of the car’s inertia was able to
recaptured as regen energy during all braking
events.
 Heat pump and cabin heating models were
developed based on energy and mass
conservation. The help pump was powered by
the battery pack and tied into the vehicle model
© 2014 EC Power, LLC. All Rights Reserved.
in Simulink. The heater was turned on for
ambient temperatures at and below 10oC, with
the cabin set point temperature set to 24 oC
(initial temperature equal to the ambient
temperature).
 Repeated cycling of the EPA Urban
Dynamometer Driving Schedule (UDDS) was
used to simulate stop and go driving. Figure 2
shows one cycle of the UDDS in miles per hour
vs. time. The vehicle sub-model converts the
vehicle speed to power demand. The propulsion
power plus the heater power add to give the
total battery pack power demand, based on the
driving and heating conditions. Figure 3 shows
the pack power over the entire vehicle drive
range at 25oC. Although a UDDS cycle was
chosen for this simulation, any other drive cycle
(HWFET, US06, etc.) can be directly dropped
into the model, and the vehicle’s response
investigated.
 The pack was assumed insulated without active
cooling under the conditions tested.
 The battery pack full charge was taken to be at
90% SOC, where regen was still possible. The
lower cutoff condition, where it was assumed
the battery could no longer be used drive the
vehicle, was taken to be 20% SOC or a cell
voltage of 3.4V (326.4V pack voltage).
Results
4.5
4
Cell Voltage (V)
Introduction
3.5
3
2.5
2
0
0.2
0.4
0.6
0.8
1
DoD
Figure 1. C/3 discharge curve for a single 70/30
LMO/NMC 33Ah cell used in the battery pack.
DoD = [1 – SOC].
1
60
400
50
390
Pack Voltage (V)
Vehicle Speed (mph)
EC Power
341 N. Science Park Rd.
State College, PA, 16803, USA
[email protected]
Ph: +1-814-861-6233
40
30
20
10
Tamb = -10oC
Tamb = 25oC
380
370
360
350
340
0
0
200
400
600
330
0
800 1000 1200 1400
time (s)
Figure 2. EPA Urban Dynamometer Driving
Schedule (UDDS) [3]. The single cycle here is
cycled repeately during simulation to mimmick
urban stop and go driving of the EV.
100
200
300
time (min)
Figure 5. Battery pack voltage at -10oC and 25oC
ambient temperatures.
1
Tamb = -10oC
Tamb = 25oC
0.8
40
SOC
Pack Power (kW)
60
20
0.6
0.4
0.2
0
0
0
-20
0
50
100
150
200
250
50
100
150
200
250
300
time (min)
300
time (min)
Figure 3. Power load on battery pack at 25oC.
Positive power is discharge (propulsion), negative
is charge (regeneration). Note no heater used at
25oC.
Figure 6. Battery pack SOC at -10oC and 25oC
ambient temperatures.
Drive Range (mi)
120
100
Heater On
80
60
40
20
0
-30
-20
-10
0
10
20
30
Temperature (oC)
Figure 4. EV drive range vs. ambient temperature
as predicted by AutoLion-ST™ for repeated
UDDS drive cycle [3].
© 2014 EC Power, LLC. All Rights Reserved.
2
EC Power
341 N. Science Park Rd.
State College, PA, 16803, USA
[email protected]
Ph: +1-814-861-6233
Heat Pump Power (kW)
5
Tamb = -15, -10, -5, 0, 5, 10 oC
4
3
2
1
0
0
50
100
150
200
250
300
time (min)
o
Cabin Temperature ( C)
30
20
over 2.5hrs equates to 8kWh, or ~ 33% of the
pack power, just to maintain cabin temperature.
The remainder of the range reduction at -10oC
comes from drivetrain inefficiencies, braking
inefficiencies, and lower pack efficiencies at
lower temperatures.
 Parametric effects of design factors such as
electrode thickness and porosity, cell chemistry
or blend ratios, thermal management strategies,
etc. can easily be investigated as part of the
design phase using AutoLion™. Using
AutoLion™, the effect of these design
parameters on not just battery performance, but
also directly on EV performance can be
investigated under different driving conditions,
ambient conditions, etc.
 A full ~ 5 hour or 100 mile EV drive simulation
took ~ 1 minute of computing time with
standard computing equipment.
10
References
0
o
Tamb = -15, -10, -5, 0, 5, 10 C
-10
-20
0
5
10
15
time (min)
Figure 7. (a) heat pump power draw and (b) cabin
air temperature (for the first 15 minutes) at
ambient temperatures between -15oC to 10oC.
Summary, Analysis, and Conclusions
 Figure 4 shows the drive range vs. ambient
temperature under urban driving conditions, as
predicted by AutoLion™. A substantial (30%
and greater) drop in range is observed when the
cabin heater is turned on at and below 10oC.
Further, at 25oC and -10oC, a drive range of 101
and 49 miles is predicted, respectively. This is
well in line with those reported by AAA for
similar vehicles, under similar conditions.
 Figures 5 and 6 give the battery pack voltage
and state of charge (SOC) at ambient/initial
temperatures of -10 and 25oC. Figures 7 (a) and
(b) give the heat pump power draw and cabin
temperatures at -15, -10, -5, 0, 5, and 10oC,
respectively. At -10oC, the heater draws ~
3.2kW power to maintain the cabin temperature
at 24oC. From figure 6 we see that at -10oC, the
SOC reaches the cutoff condition of 20% at ~
150 min, or 2.5hrs. The heater using 3.2kW
© 2014 EC Power, LLC. All Rights Reserved.
[1] Heather Hunter, AAA News Room, “Extreme
Temperatures Affect Electric Vehicle Driving Range,
AAA Says,” March 20, 2014
http://newsroom.aaa.com/2014/03/extremetemperatures-affect-electric-vehicle-driving-rangeaaa-says/
[2] Consumer Reports News, “Winter chills limit
range of the Tesla Model S electric car,” February 15,
2013.
http://www.consumerreports.org/cro/news/2013/02/w
inter-chills-limit-range-of-the-tesla-model-s-electriccar/index.htm
[3] EPA Urban Dynamometer Driving Schedule
(UDDS), also referred to as the “LA4,”
http://www.epa.gov/nvfel/testing/dynamometer.htm
3