electric motor thermal management for electric … motor thermal management for electric traction...
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ELECTRIC MOTOR THERMAL MANAGEMENT FOR ELECTRIC TRACTION DRIVES Kevin Bennion, Justin Cousineau, Gilbert Moreno National Renewable Energy Laboratory
SAE 2014 Thermal Management Systems Symposium September 22–24, 2014 Denver, CO
14TMSS-0086
NREL/PR-5400-62919 NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC
SAE INTERNATIONAL
Relevance – Why Motor Cooling?
• Current Density
• Magnet Cost
o Price variability
o Rare-earth materials
• Material Costs
• Reliability
• Efficiency
2
Stator Cooling Jacket
Stator End Winding
Rotor Stator
Sample electric traction drive motor.
Photo Credit: Kevin Bennion, NREL
Photo Credit: Kevin Bennion, NREL
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Motor Thermal Management – Passive and Active Cooling
3
Passive Thermal Design
Active Convective
Cooling
Motor Thermal
Management
Passive Thermal Design •Motor geometry •Material thermal properties •Thermal interfaces
Active Convective Cooling •Cooling location •Heat transfer coefficients •Available coolant •Parasitic power
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Background – Motor Thermal Management Challenges
Problem Extracting heat from within the motor to protect motor and enable high power density
Example 4 to 9 kW of heat could be produced with an 80-kW motor operating with an efficiency between 90% and 95% [1].
4
ATF: Automatic Transmission Fluid
Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
[1] S. Oki, S. Ishikawa, and T. Ikemi, “Development of High-Power and High-Efficiency Motor for a Newly Developed Electric Vehicle,” SAE International, 2012-01-0342, Apr. 2012.
SAE INTERNATIONAL
Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
Background – Motor Thermal Management Challenges
Problem Extracting heat from within the motor to protect motor and enable high power density
Challenges 1. Orthotropic (direction
dependent) thermal conductivity of lamination stacks
1
1
5
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Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
Background – Motor Thermal Management Challenges
Problem Extracting heat from within the motor to protect motor and enable high power density
Challenges 1. Orthotropic (direction
dependent) thermal conductivity of lamination stacks
2. Orthotropic thermal conductivity of slot windings
1
1
2
6
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Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
Background – Motor Thermal Management Challenges
Problem Extracting heat from within the motor to protect motor and enable high power density
Challenges 1. Orthotropic (direction
dependent) thermal conductivity of lamination stacks
2. Orthotropic thermal conductivity of slot windings
3. Orthotropic thermal conductivity of end windings
1
1
2 3
7
SAE INTERNATIONAL
Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
Background – Motor Thermal Management Challenges
Problem Extracting heat from within the motor to protect motor and enable high power density
Challenges 1. Orthotropic (direction
dependent) thermal conductivity of lamination stacks
2. Orthotropic thermal conductivity of slot windings
3. Orthotropic thermal conductivity of end windings
4. Convective heat transfer coefficients for ATF cooling
4
1
1
2 3
8
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Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
Background – Motor Thermal Management Challenges
Problem Extracting heat from within the motor to protect motor and enable high power density
Challenges 1. Orthotropic (direction
dependent) thermal conductivity of lamination stacks
2. Orthotropic thermal conductivity of slot windings
3. Orthotropic thermal conductivity of end windings
4. Convective heat transfer coefficients for ATF cooling
5. Thermal contact resistance of stator-case contact
4
1
1
2 3
5
9
SAE INTERNATIONAL
Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
Background – Motor Thermal Management Challenges
Problem Extracting heat from within the motor to protect motor and enable high power density
Challenges 1. Orthotropic (direction
dependent) thermal conductivity of lamination stacks
2. Orthotropic thermal conductivity of slot windings
3. Orthotropic thermal conductivity of end windings
4. Convective heat transfer coefficients for ATF cooling
5. Thermal contact resistance of stator-case contact
6. Cooling jacket performance
4
1
1
2 3
5
6
10
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Research Objective
Problem
Research Tasks
Objective
Support broad industry demand for data, analytical methods, and experimental techniques to improve and better understand motor thermal management
11
Stator Laminations
Slot Winding
Rotor Laminations Rotor
Hub
Case
Air Gap
Stator-Case Contact
Nozzle/Orifice
ATF Impingement
Shaft ATF Flow
ATF Flow
Stator Cooling Jacket
End Winding
Motor Axis
Motor Cooling Section View
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Research Focus
•Measure convective heat transfer coefficients for ATF cooling of end windings •Measure interface thermal resistances
and orthotropic thermal conductivity of materials
Support broad industry demand for data to improve and better understand motor thermal management
Objective
Research Tasks
Automatic Transmission Fluid Heat Transfer
Material and Thermal Interface Testing
Photo Credit: Jana Jeffers, NREL
Photo Credit: Justin Cousineau, NREL
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Active Convective Cooling – ATF Heat Transfer Coefficients
• Measure convective heat transfer coefficients for ATF cooling of end windings
Photo Credit: Kevin Bennion, NREL Photo Credit: Jana Jeffers, NREL
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Direct impingement on target surfaces
Impingement on motor end windings
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ATF Impingement Test Section
D (mm) d (mm) S (mm) S /d D /d12.7 2.06 10 5 6.2
Test Sample
Nozzle Plate: Orifice Diameter
(d) = 2 mm
Sample Holder/Insulation
Resistance Heater Assembly
Fluid Inlet
Aluminum Vessel
ThermocouplesS = 10 mm
D = 12.7 mm
Oil Impingement Test Section Schematic Photo During Operation
Photo Credit: Jana Jeffers, NREL
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ATF Impingement Target Surfaces
Baseline 18 AWG 22 AWG 26 AWG
Radius (wire and insulation), mm
N/A 0.547 0.351 0.226
Total wetted surface area, mm2 126.7 148.2 143.3 139.2
AWG = American Wire Gauge
18 AWG 22 AWG 26 AWG
Credit: Gilbert Moreno, NREL
15
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Note: Heat transfer coefficient calculated from the base projected area (not wetted area)
50°C Inlet Temperature
0
2,000
4,000
6,000
8,000
10,000
12,000
0 2 4 6 8 10 12
Hea
t Tra
nsfe
r Coe
ffici
ent [
W/m
2 K]
Velocity [m/s]
18 AWG22 AWG26 AWGBaseline
ATF Heat Transfer Coefficients
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ATF Heat Transfer Coefficients
ATF flowing over surface
ATF deflecting off surface
Note: ATF viscosity decreases as temperature increases
Photo Credit: Jana Jeffers, NREL
Photo Credit: Jana Jeffers, NREL
0
2,000
4,000
6,000
8,000
10,000
12,000
0 2 4 6 8 10 12
Heat
Tra
nsfe
r Coe
ffici
ent [
W/m
2 K]
Velocity [m/s]
50°C70°C90°C
18 AWG sample data for all inlet temperatures
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Passive Thermal Design – Material and Interface Thermal Measurements
• Measure interface thermal resistances and orthotropic thermal conductivity of materials
Photo Credit: Justin Cousineau, NREL
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• Stacked lamination thermal conductivity
• Slot windings
Effective thermal properties for motor
design and simulation
Photo Credit: Kevin Bennion, NREL Photo Credit: Kevin Bennion, NREL
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Passive Thermal Design – Effective Through-Stack Thermal Conductivity
Measured Stack Thermal Resistance
Lamination-to-Lamination Thermal Contact Resistance
Effective Through-Stack Thermal Conductivity
Cold Plate
Hot Plate
Copper Spreader
Copper Spreader
Copper Metering Block
Copper Metering Block
Lamination Stack
Thermal Grease
Thermal Grease
Force Applied
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Photo Credit: Justin Cousineau, NREL
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Passive Thermal Design – Effective Through-Stack Thermal Conductivity
Measured Stack Thermal Resistance
Lamination-to-Lamination Thermal Contact Resistance
Effective Through-Stack Thermal Conductivity
0
500
1000
1500
2000
2500
0 2 4 6 8 10
Mea
sure
d La
min
atio
n St
ack
Ther
mal
Res
istan
ce (m
m²-
K/W
]
Number of Contacts
M19 29 Gauge, 138 kPa Data
Data with Systematic Error
Weighted Curve Fit
Cold Plate
Hot Plate
Copper Spreader
Copper Spreader
Copper Metering Block
Copper Metering Block
Lamination Stack
Thermal Grease
Thermal Grease
Force Applied
Error bars represent 95% confidence level
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Passive Thermal Design - Effective Through-Stack Thermal Conductivity
0
50
100
150
200
250
300
350
138 276 414 552
Lam
inat
ion-
to-L
amin
atio
n Th
erm
al
Cont
act R
esist
ance
[mm
²-K/
W]
Pressure [kPa]
M19 26 Gauge
M19 29 Gauge
HF10
Arnon7
Error bars represent 95% confidence level
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Measured Stack Thermal Resistance
Lamination-to-Lamination Thermal Contact Resistance
Effective Through-Stack Thermal Conductivity
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Passive Thermal Design – Effective Through-Stack Thermal Conductivity
1.51.71.92.12.32.52.72.93.13.3
0 10 20 30 40 50Thro
ugh-
Stac
k Th
erm
al C
ondu
ctiv
ity
[W/m
-K]
Number of Laminations (NL)
M19 29 Gauge, 138 kPa Example
Effective Through-Stack Thermal Conductivity
Asymptote(𝑁𝑁𝐿𝐿 → ∞)
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Measured Stack Thermal Resistance
Lamination-to-Lamination Thermal Contact Resistance
Effective Through-Stack Thermal Conductivity
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Passive Thermal Design – Effective Through-Stack Thermal Conductivity
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
0 200 400 600
Asym
ptot
ic T
hrou
gh-S
tack
The
rmal
Co
nduc
tivity
[W/m
-K]
Pressure [kPa]
M19 26 Gauge
M19 29 Gauge
HF10
Arnon7
Error bars represent 95% confidence level
23
Measured Stack Thermal Resistance
Lamination-to-Lamination Thermal Contact Resistance
Effective Through-Stack Thermal Conductivity
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Passive Thermal Design – Effective In-Plane Lamination Stack Thermal Conductivity
• Measured in-plane thermal conductivity of lamination stacks provided by Oak Ridge National Laboratory (ORNL)
Cold Plate
Hot Plate
Copper Spreader
Copper Spreader
Copper Metering Block
Copper Metering Block
Lamination Stack
Thermal Grease
Thermal Grease
Force Applied
Photo Credit: Justin Cousineau, NREL
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Passive Thermal Design – Effective In-Plane Lamination Stack Thermal Conductivity
• Confirmed in-plane thermal conductivity is close to bulk material thermal conductivity
1. Based on measured thermal conductivity of similar material 2. Calculated assuming 99% stacking factor 3. Average of measured orthotropic property in setup shown in figure
21.9 21.7 21.8
0.0
5.0
10.0
15.0
20.0
25.0
BulkMaterial
CalculatedValue
Measured
In-P
lane
The
rmal
Con
duct
ivity
[W/m
-K]
M19 29 Gauge Laminations
1 2
3
25
Photo Credit: Justin Cousineau, NREL
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Passive Thermal Design – Effective Wire Bundle Cross-Slot Thermal Conductivity
• Measured cross-slot thermal conductivity of wire bundles prepared and provided by ORNL
Cold Plate
Hot Plate
Copper Spreader
Copper Spreader
Copper Metering Block
Copper Metering Block
Wire Bundle
Thermal Grease
Thermal Grease
Force Applied
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Photo Credits: Justin Cousineau, NREL
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Passive Thermal Design – Effective Wire Bundle Cross-Slot Thermal Conductivity
Note: Wire fill factor includes copper and insulation
0.48
1.06
0.66
0.54
0.98
0.60
0
0.2
0.4
0.6
0.8
1
1.2
Test Results Model: PerfectFill Factor
Model: 50%Voiding
Cro
ss-S
lot T
herm
al C
ondu
ctiv
ity (W
/m-K
)
Wire Fill Factor: 0.67 Wire Fill Factor: 0.63
• The agreement between model and experimental results depends on assumptions for fill factor, voiding, and thermal contact resistance
• Modeling approach appears to match, but additional testing is needed
Photo Credits: Justin Cousineau, NREL
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Conclusion
Relevance • Supports transition to more electric-drive vehicles with higher continuous power
requirements • Enables improved performance of non-rare earth motors and supports lower cost through
reduction of rare earth materials used to meet temperature requirements (dysprosium)
Technical Accomplishments • Received sample motor materials from ORNL and measured orthotropic thermal
conductivity • Completed expanded lamination thermal tests • Measured ATF heat transfer convection coefficients on target surfaces • Received ATF fluid property data from Ford Motor Company to support future work to
develop correlations and computational fluid dynamics models
Collaborations • Motor industry representatives: manufacturers, researchers, and end users (light-duty and
medium/heavy-duty applications) • Oak Ridge National Laboratory
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For more information, contact:
Principal Investigator Kevin Bennion [email protected] Phone: (303) 275-4447
APEEM Task Leader:
Sreekant Narumanchi [email protected] Phone: (303) 275-4062
Acknowledgments:
Susan Rogers and Steven Boyd, U.S. Department of Energy Team Members:
Justin Cousineau (NREL) Jana Jeffers (NREL) Charlie King (NREL) Gilbert Moreno (NREL) Tim Burress (ORNL) Andy Wereszczak (ORNL)