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Losses in Electric Propulsion Motors and How to Reduce Them
Rafal Wrobel
1
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Loss components in electrical machines:
• mechanical loss
bearing loss
windage and drag loss
• electromagnetic loss
winding loss
core loss
permanent magnet loss
2
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Winding loss effects at ac operation:
• skin effect
• proximity effect
• effect from rotating rotor
3
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How to assess significance of the ac winding effects for a
particular machine design?
• high-speed operation
• high-frequency operation
• other measures or indicators, e.g. skin depth
4
𝛿=𝜌
𝜋𝜇𝑓
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How to derive the ac winding loss components?
• theoretical approach
analytical formulae
numerical techniques, e.g. FEM
• experimental method
tests on machine subassemblies
5
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How to quantify the ac winding effects?
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𝑃𝑎𝑐 = 𝑃𝑑𝑐 + 𝑃 𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑃𝑎𝑐𝑃𝑑𝑐
𝑇=𝑐𝑜𝑛𝑠𝑡
=𝑅𝑎𝑐𝑅𝑑𝑐
𝑇=𝑐𝑜𝑛𝑠𝑡
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Temperature dependence of loss at ac operation:
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𝑃𝑎𝑐 𝑇 = 𝐼2𝑅𝑑𝑐 𝑇0 1 + 𝛼 𝑇 − 𝑇0 +
𝐼2 𝑅𝑑𝑐 𝑇0
𝑅𝑎𝑐𝑅𝑑𝑐 𝑇0
− 1
1 + 𝛼 𝑇 − 𝑇0𝛽
𝜌 𝑇
= 𝜌 𝑇0
1 + 𝛼 𝑇 − 𝑇0
𝑃𝑑𝑐 𝑇
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠 𝑇
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8
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐
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20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐 𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑛 = 1000𝑟𝑝𝑚
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10
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐 𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑛 = 2000𝑟𝑝𝑚
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑃𝑑𝑐
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20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐 𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑛 = 3000𝑟𝑝𝑚
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑃𝑑𝑐
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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er
loss
𝑃𝑎𝑐
𝑃𝑑𝑐 𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
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12
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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loss
𝑃𝑑𝑐
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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er
loss
𝑃𝑑𝑐 𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑛 = 4000𝑟𝑝𝑚
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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er
loss
𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑃𝑑𝑐
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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er
loss
𝑃𝑎𝑐
𝑃𝑑𝑐 𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
20 40 60 80 100 120 140 160 180 200
Temperature [C]
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er
loss
𝑃𝑎𝑐
𝑃𝑎𝑐 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝑃𝑑𝑐
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Motor 1 Motor 2
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Motor 1 Motor 2
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Motor 1 Motor 2
Rated speed nN = 4000rpm nN = 10000rpm
Rated power PN = 7.5kW PN = 60kW
Outer diameter DO/D = 155mm DO/D = 230mm
Active length lA = 120mm lA = 160mm
Number of poles p = 6 p = 8
Number of slots q = 18 q = 12
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Experimental setup
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DC linkVariable frequency
voltage source inverterLC filter
Stator/Winding assembly
Power analyser
CTs
Data acquisition system
Thermocouples
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Motor 1
0 50 100 150 200 2501
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
Frequency [Hz]
Rac/R
dc
TW
= 20C
TW
= 40C
TW
= 60C
TW
= 80C
TW
= 100C
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18
Motor 2
0 100 200 300 400 500 600 700 800
2
4
6
8
10
12
14
Frequency [Hz]
Rac/R
dc
TW
= 20C
TW
= 40C
TW
= 60C
TW
= 80C
TW
= 100C
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Motorette setup
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Multi-stranded copper bundle
Profiled rectangular copper conductor
𝑅𝑎𝑐𝑅𝑑𝑐
200𝐶,700𝐻𝑧
= 4.9
𝑅𝑎𝑐𝑅𝑑𝑐
1000𝐶,700𝐻𝑧
= 4.4
𝑅𝑎𝑐𝑅𝑑𝑐
200𝐶,700𝐻𝑧
= 11.6
𝑅𝑎𝑐𝑅𝑑𝑐
1000𝐶,700𝐻𝑧
= 9.4
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Motor 1 Motor 2
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0 50 100 150 200 2501
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
1.45
1.5
Frequency [Hz]
Pac/P
dc
Stator/winding setup
Motor setup - maximum torque/Ampere
Motor setup - short-circuit
Motor 1
𝑇 = 200𝐶
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0 100 200 300 400 500 600 7000
2
4
6
8
10
12
Frequency [Hz]
Pac/P
dc
Stator/winding setup
Motor setup - maximum torque/Ampere
Motor setup - short-circuit
Motorette setup
Motor 2
𝑇 = 200𝐶
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0 100 200 300 400 500 600 7000
0.2
0.4
0.6
0.8
1
1.2
1.4
Frequency [Hz]
Pac/P
dc
Motor setup 1 - open-circuit
Motor setup 2 - open-circuit
𝑇 = 200𝐶
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So, how to reduce the winding loss at ac operation?
• better understanding of the loss mechanisms
• better understanding of the initial design requirements
• accounting for the multi-physics phenomena in design
process
• appropriate use of the existing techniques for loss
mitigation
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