ev traction motor comparison - techno frontier 2013 - m burwell - international copper accociation
TRANSCRIPT
Performance/cost comparison of induction-motor & permanent-magnet-motor in a hybrid electric car Malcolm Burwell – International Copper Association James Goss, Mircea Popescu - Motor Design Ltd July 2013 - Tokyo
Is it time for change in the traction motor supply industry?
“[Our] survey of 123 manufacturers shows far too few making asynchronous or switched reluctance synchronous motors... this is an industry structured for the past that is going to have a very nasty surprise when the future comes.” *
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 2
* Source: IDTechEx research report “Electric Motors for Electric Vehicles 2013-2023: Forecasts, Technologies, Players” www.IDTechEx.com/emotors
Motor-types sold by suppliers of vehicle
traction motors *
The challenge for electric traction motors: rare earth cost-levels and cost-volatility
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 3
Source: metal-pages.com, Kidela Capital
0
500
1000
1500
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Ne Oxide Dy Oxide
Neodymium Oxide
Dysprosium Oxide
Copper (for reference)
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Permanent Magnet Motor Materials (“rare earths”)
$480/kg $60/kg
$ per kg
$7/kg
Background to this work
Today, the permanent magnet motor is the leading choice for traction drives in hybrid vehicles But permanent magnet motors have challenges: • High costs • Volatile costs • Uncertain long term availability of rare earth permanent magnets This makes alternative magnet-free motor architectures of great interest The induction motor is one such magnet-free architecture 4 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
This presentation
The work presented here compares two equivalent 50kW tractions motors for use in hybrid electric vehicles: a permanent magnet motor and an equivalent induction motor
• The main analysis has copper as the rotor cage material of an induction motor • Motoring and generating modes are modelled using standard drive cycles • Important outputs of the work, for each motor type, are:
• Lifetime energy losses and costs • Relative component performance parameters, weights and costs
• Top-level comments on aluminium cages are presented at the end
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 5
Overview of the analysis covered in this presentation
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1. Driving cycles
2. Vehicle Model
3. Powertrain Model
Magnetics
Induction Motor
Permanent Magnet Motor
4. Motor Models
5. Motor Performance
7. Inverter Currents
9. Battery Capacities
8. Motor Weights & Costs
10. Breakeven Analysis
6. Energy Losses & Costs
Heat Flows
Materials per motor Permanent magnet motor
Copper rotor induction motor
Weight Cost Weight CostStator Copper 4.5 kg $31 9.1 kg $64
Steel 24 kg $24 24 kg $24Permanent magnets (2011/2013 prices)
1.3 kg $200-540 0 0
Rotor cage 0 0 8.4 kg $59Increased inverter cost - 0 - $50
Total 29.8 kg(100%)
$260-590 41.5 kg(140%)
$200
Reduction of consumer purchase price*
- 0 - $150-980
Total losses in the motor Permanent magnet motor
Copper rotor induction
motorCity driving over 120,000 miles (UDDS) 1270 kWh 2240 kWh
Highway driving over 120,000 miles (HWFET) 610 kWh 1250 kWh
Aggressive driving over 120,000 miles (US06) 1430 kWh 2510 kWh
Combined average losses over 120,000 miles 1100 kWh 2000 kWh
Extra energy cost (grid price of $0.25/kWh) 0 $220Extra energy cost (internal combustion engine cost of $0.294/kWh) 0 $260
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p (
p
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Main conclusions from this work
• Comparing a 50kW copper-rotor induction motor to a 50kW permanent magnet motor: • No rare earth metals used • -25% torque density • +40% weight • +10-15% peak inverter current
• However, the induction motor is a good alternative because: • Total motor+inverter unit costs are $60-$390 less (=$150-980 lower sticker price) • It uses only $260 in extra energy over 120,000 miles • Increased inverter costs are modest at ~$50/vehicle
• Battery size: • Can optionally be increased to match increased motor losses • Unit cost savings are larger than increased battery costs up to 27kWh battery size
• Using aluminum instead of copper in the rotor of a 50kW induction motor for an HEV: • Increases losses by 4% • Lowers torque density by 5%
7 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
1. Vehicle drive cycles
Three standard drive cycles are used for the comparison of two traction motors: a permanent magnet motor and a copper rotor induction motor. The 120,000/10year vehicle life is assumed to be composed equally of these three types of driving
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 8
Driving cycle Distance Average
speed City
(UDDS) 7.5 miles 20 mph
Highway (HWFET) 10.3 miles 48 mph
Aggressive (US06)
8.0 miles
48 mph
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2. Vehicle Model
Frolling
Faero
Ftraction
9 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
A standard vehicle model is used to convert drive cycle information into powertrain torque/speed requirements.
3.1 Powertrain model
A standard two motor/generator hybrid powertrain architecture is used
• Consists of two electrical motor/generators, MG1 and MG2 and an internal combustion engine, all connected through a planetary gear set
• Rotational speed of the internal combustion engine (ICE) is decoupled from the vehicle speed to maximise efficiency
• We analyze MG2 for performance/cost
10 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
• We assume that MG2: • Has a rated power of 50kW • Couples to the drive wheels through
a fixed gear ratio • Provides 30% of motoring torque • Recovers up to 250Nm braking
torque • The ICE and brakes supply the rest
3.2 Motor torques/speeds produced during driving cycles
11 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
By applying the vehicle and powertrain models we convert the driving cycle data into motor torque/speed data points. One data point is produced for each one second of driving cycle
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4.1 Magnetic models of permanent magnet motor and induction motor
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Stator OD = 270mm Rotor OD = 160mm
Stack Length = 84mm
Stator OD = 270mm Rotor OD = 180mm
Stack Length = 105mm
Permanent Magnet Motor
Copper Rotor Induction Motor
8 Poles 8 48 Stator Slots 48 - Rotor Bars 62
The two motor types were modeled for similar torque/speed performance: same stator outside diameters, same cooling requirements but different stack lengths
4.2 Reference permanent magnet motor model
The modelled permanent magnet motor is a well-documented actual motor used in a production hybrid vehicle.
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The model of the permanent magnet motor was validated against test data from the actual motor
4.3 Validation of the motor performance model
Test data from actual motor (including mechanical losses)
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14 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
Our analysis continues using motor performance which excludes mechanical losses
Model and actual data correspond well
4.4 Thermal Performance Comparison
Steady-state thermal analysis was used to equalize cooling system requirements for both motors at a 118 Nm/900 rpm operating point
Permanent Magnet Motor
Copper Rotor Induction Motor
92% Efficiency 88%
780 W Stator Copper Loss 940 W
0 W Rotor Loss 230 W
0 W Stray Load Loss 140 W
100 W Iron Loss 180 W
880 W Total Loss 1490 W
105°C Coolant Temperature 105°C
2.4 gallons/min Coolant Flow Rate 2.4 gallons/min
156°C Maximum Winding Temp 156°C
15 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
5.1 Torque/speed/efficiency maps of the permanent magnet motor and induction motor
The two motors have similar torque/speed performance, with the induction motor having ~5% lower efficiencies
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 16
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5.2 Torque/speed loads during drive cycles: permanent magnet motor
Torque/speed points from the vehicle/powertrain model of the driving cycles are applied to the performance map of the permanent magnet motor to determine total motor losses during driving:
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 17
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Per
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5.3 Torque/speed loads during drive cycles: copper rotor induction motor
Torque/speed points from the vehicle/powertrain model of the driving cycles are applied to the performance map of the copper rotor induction motor to determine total motor losses during driving:
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 18
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86
86
86
86 86 86
87
87
87
87
87
87 87 87
88
88
88
88
88
88 8888
89
89
89
89
89 8989
90
90
90
90
90 90
90
91
91
91
91
91
92
92
92
Mot
orin
g to
rque
(Nm
) G
ener
atin
g to
rque
(Nm
)
Speed (rpm) 0 1000 2000 3000 4000 5000 6000
50
100
150
200
250
300
0
0
0
60
6060
60
60
60
70
7070
70
70
70
808080
8080
80
80
80
818181
8181
81
81
81
828282
8282
82
82
82
838383
8383
83
83
83
848484
8484
84
84
84
858585
8585
85
85
85
868686
8686
86
86
86
878787
87
87
87
87
87
888888
88
88
88
88
88
898989
89
89
89
89
89
90
90
90
90
9090
90
91
91
91
9191
91
92
92
92
9293
g y p
-300
-250
-200
-150
-100
-50
0
0
0
0
60
60
60
60
60
60
70 70
70
70
70
70
70
80
80
80
8080
80 80 80
81
81
81
8181
81 81 81
82
82
82
8282
82 82 82
83
83
83
8383
83 83 83
84
84
84
84
84
84 84 84
85
85
85
85
85
85 85 85
86
86
86
86
86
86 86 86
87
87
87
87
87
87 87 87
88
88
88
88
88
88 8888
89
89
89
89
89 8989
90
90
90
9090 90
90
91
91
9191
91
92
92
92
Mot
orin
g to
rque
(Nm
) G
ener
atin
g to
rque
(Nm
)
Speed (rpm) 0 1000 2000 3000 4000 5000 60000
50
100
150
200
250
300
0
0
0
60
6060
60
60
60
70
7070
70
70
70
808080
8080
80
80
80
818181
8181
81
81
81
828282
8282
82
82
82
838383
8383
83
83
83
848484
8484
84
84
84
858585
8585
85
85
85
868686
8686
86
86
86
878787
87
87
87
87
87
888888
88
88
88
88
88
898989
89
89
89
89
89
90
90
90
90
9090
90
91
91
91
9191
91
92
92
92
92
93
g y p
Effi
cien
cy (%
)
80
82
84
86
88
90
92
94
96
-300
-250
-200
-150
-100
-50
0
0
0
0
60
60
60
60
60
60
70 70
70
70
70
70
70
80
80
80
8080
80 80 80
81
81
81
8181
81 81 81
82
82
82
8282
82 82 82
83
83
83
8383
83 83 83
84
84
84
84
84
84 84 84
85
85
85
85
85
85 85 85
86
86
86
86
86
86 86 86
87
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87 87 87
88
88
88
88
88
88 8888
89
89
89
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89 8989
90
90
90
90
90 90
90
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91
91
92
92
92
Mot
orin
g to
rque
(Nm
) G
ener
atin
g to
rque
(Nm
)
Speed (rpm)
City driving cycle loads (UDDS)
Highway driving cycle loads (HWFET)
Aggressive driving cycle loads (US06)
Cop
per r
otor
indu
ctio
n m
otor
6.1 Motor losses during driving cycles
From the motor models, cumulative losses during each driving cycle can be calculated:
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 19
Cum
ulat
ive
loss
es o
ver d
rivin
g cy
cle
(Wh)
Time (seconds)
City driving cycle losses (UDDS)
Highway driving cycle losses (HWFET)
Aggressive driving cycle losses (US06)
Cum
ulat
ive
loss
es o
ver d
rivin
g cy
cle
(Wh)
Time (seconds)
Cum
ulat
ive
loss
es o
ver d
rivin
g cy
cle
(Wh)
Time (seconds)
Copper rotor induction motor Permanent magnet motor
6.2 Combined losses over life of the motor
Total losses in the motor Permanent magnet motor
Copper rotor induction
motor City driving over 120,000 miles (UDDS) 1270 kWh 2240 kWh
Highway driving over 120,000 miles (HWFET) 610 kWh 1250 kWh
Aggressive driving over 120,000 miles (US06) 1430 kWh 2510 kWh
Combined average losses over 120,000 miles 1100 kWh 2000 kWh
Extra energy cost (grid price of $0.25/kWh) 0 $220 Extra energy cost (internal combustion engine cost of $0.294/kWh) 0 $260
The total difference in electrical running costs between the permanent magnet motor and the copper rotor induction motor are $220-$260. Over a typical lifetime of 120,000miles and 10 years, this is an insignificant cost.
20 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
7. Cost of increased inverter for copper motor induction motor
The copper rotor induction motor/generator requires 10-15% more current to achieve maximum torque. This requires that the power electronics cost ~$50 more than for a permanent magnet motor.
21 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
Mot
orin
g to
rque
(Nm
)
Speed (rpm)
Permanent magnet motor
Pea
k ph
ase
curr
ent (
A)
Mot
orin
g to
rque
(Nm
)
Speed (rpm)
Pea
k ph
ase
curr
ent (
A)
Copper rotor induction motor
8. Component cost comparison
The copper rotor induction motor saves between $60 (at 2013 magnet prices) and $390 (at 2011 magnet prices) costs per vehicle. This translates into $150-980 purchase price savings for the consumer
Materials per motor Permanent magnet motor
Copper rotor induction motor
Weight Cost Weight Cost Stator Copper 4.5 kg $31 9.1 kg $64
Steel 24 kg $24 24 kg $24 Permanent magnets (2011/2013 prices)
1.3 kg $200-540 0 0
Rotor cage 0 0 8.4 kg $59 Increased inverter cost - 0 - $50
Total 29.8 kg (100%)
$260-590 41.5 kg (140%)
$200
Reduction in consumer purchase price*
- 0 - $150-980
22 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
* Assumes materials-cost/consumer-price ratio = 40%
9. Cost of increased battery capacity to cover increased motor losses
Using a copper rotor induction motor can require the vehicle designer to increase the battery size by ~7%. This would allow a customer to perceive no difference in overall vehicle performance.
Key assumptions used in costing the required increase in battery capacity:
• Motor must at some time provide all motoring and braking torque in the highway driving cycle (like a plug-in hybrid electric vehicle)
• Induction motor uses 7% more motoring energy than a permanent magnet motor
• Induction motor recovers 6% less braking energy than the permanent magnet motor
• Total braking energy is 20% of the motoring energy over the driving cycle • 75% of battery energy is used for motoring, 25% for auxiliary systems
(cabin conditioning, lights, radio, electronics)
23 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
10. Break-even for using copper motor induction motor
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 24
If the designer chooses to increase battery size for a 50kW system, a copper rotor induction motor saves total vehicle costs when the battery size for a permanent magnet motor system is less than 27kWh
* Assumes 2020 battery pricing of $200/kWh and 7% battery capacity increase for copper rotor induction motor
0
100
200
300
400
500
600
0 10 20 30 40
Indu
ctio
n m
otor
cos
t sav
ings
($)
Permanent magnet motor battery capacity (kWh)
Additional battery cost*
$390 unit cost savings (2011 Rare Earth prices)
$60 unit cost savings(2013 Rare Earth prices)
2013 break-even
2011 break-even
Possible use of aluminum in the rotor of an induction motor
25 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
Aluminum has only 56% of the conductivity of copper, which leads to an inferior performance when used in the rotor of an induction motor. In a first-pass analysis of a 50kW aluminum rotor induction motor, losses were 4% higher and power/torque densities 5% lower than the equivalent copper rotor motor.
0
0
0
60
6060
60
60
60
70
7070
70
70
70
808080
8080
80
80
80
818181
8181
81
81
81
828282
8282
82
82
82
838383
8383
83
83
83
848484
8484
84
84
84
858585
8585
85
85
85
868686
8686
86
86
86
878787
87
87
87
87
87
888888
88
88
88
88
88
898989
89
89
89
89
89
90
90
90
90
9090
90
91
91
91
9191
91
92
92
92
92
93
0 1000 2000 3000 4000 5000 60000
50
100
150
200
250
300E
ffici
ency
(%)
80
82
84
86
88
90
92
94
96
Mot
orin
g to
rque
(Nm
)
Speed (rpm)
Copper rotor induction motor
0
0
0
6060
60
60
60
7070
70
70
70
808080
8080
80
80
80
818181
8181
81
81
81
828282
8282
82
82
82
838383
8383
83
83
83
848484
8484
84
84
84
858585
85
85
85
85
85
868686
8686
86
86
86
878787
87
87
87
87
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888888
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88
88
898989
89
89
89
89
89
90
90
90
90
9090
90
91
91
91
91
91
92
9292
0 1000 2000 3000 4000 5000 6000
50
100
150
200
250
300
Effi
cien
cy (%
)
80
82
84
86
88
90
92
94
96
Mot
orin
g to
rque
(Nm
)
Speed (rpm)
Aluminum rotor induction motor
Main conclusions from this work
• Comparing a 50kW copper-rotor induction motor to a 50kW permanent magnet motor: • No rare earth metals used • -25% torque density • +40% weight • +10-15% peak inverter current
• However, the induction motor is a good alternative because: • Total motor+inverter unit costs are $60-$390 less (=$150-980 lower sticker price) • It uses only $260 in extra energy over 120,000 miles • Increased inverter costs are modest at ~$50/vehicle
• Battery size: • Can optionally be increased to match increased motor losses • Unit cost savings are larger than increased battery costs up to 27kWh battery size
• Using aluminum instead of copper in the rotor of a 50kW induction motor for an HEV: • Increases losses by 4% • Lowers torque density by 5%
26 | Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013
Thank you
| Comparison of IM & PMM in a hybrid electric car - Tokyo - July 2013 27
For more information please contact
Phone: +1 781 526 5027
[email protected] [email protected] Phone: +44 1691 623305