This document discusses permanent magnet machines. It begins by defining permanent magnets and their properties. It then covers classifications of permanent magnet machines and differences compared to other machine types. Calculation methods like analytical and finite element modeling are also discussed. Key issues addressed include demagnetization risks, material availability and costs. The document concludes permanent magnet machines provide benefits of high efficiency and power density but also challenges around demagnetization and material sourcing.

1. Technology
Designs aspects of PM machines
Henk Polinder
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2. Structure
1 Permanent magnets
2 Classification of PM machines
3 What is different from other types of machines
4 Calculation methods
5 Issues
6 Conclusions
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3. What is a permanent magnet?
• Source of magnetomotive force
• Makes magnetic field without a current
Bm   0  rm H m  Br
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4. Permanent magnet BH curves
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5. Permanent magnets: demagnetization
/ temperature
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6. Permanent magnet properties
Br HcB dBr/dT dHcB/dT ρ Cost
(T) (kA/m) (%/K) (%/K) (μΩm) (€/kg)
Ferrite 0,4 -250 -0,2 +0,34 1012 2
Alnico 1,2 -130 -0,05 -0,25 0,5 20
SmCo 1,0 -750 -0,02 -0,03 0,5 100
NdFeB 1,4 -1000 -0,12 -0,55 1,4 ???
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7. Structure
1 Permanent magnets
2 Classification of PM machines
3 What is different from other types of machines
4 Calculation methods
5 Issues
6 Conclusions
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8. Classification
• DC mechanical commutator
• Iron armature
• Hollow rotor
• Disc armature
• AC electronic commutation PMSM / Brushless DC
• Surface mounted / embedded magnets
• Distributed / concentrated windings
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9. Brushed DC
• Iron armature
• Disc armature
• Hollow rotor
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10. PM AC motor
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11. Classification
• Brushes / brushless
• Brush wear / inverter cost
• Air gap winding / teeth
• cogging / force density
• Radial flux / axial flux
• available space / cost
• Rotating / linear
• performance / cost
• Brushless DCM / PMSM
• torque ripple
• Surface mounted magnets / embedded
• flux weakening
• Distributed / fractional pitch concentrated windings
• cost / losses
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12. PMSM or BDCM
PMSM:
- distributed windings
- sinusoidal voltage
- sinusoidal currents
- continuous position sensor
- smooth force
BDCM:
- concentrated windings
- trapezoidal voltage
- rectangular currents
- 6 step position sensor
- force ripple
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13. Rotor layouts
1 surface mounted magnets
2 inset magnets
3 embedded magnets
4 embedded magnets
Embedded:
-Flux weakening
-Flux concentration
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14. Concentrated fractional pitch
windings
• Reduces cost
• Increases losses in back iron
and magnets
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15. Range extender: concentrated
coils, embedded magnets
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16. Structure
1 Permanent magnets
2 Classification of PM machines
3 What is different from other types of machines
4 Calculation methods
5 Issues
6 Conclusions
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17. Force density
P   g T   g rg F  2 g rg2l g Fd  2 gVg Fd
Fd  25  50 kN/m 2
P
Vg  r l 
2
2 g Fd
g g
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18. Differences with other machines
Permanent magnets make it possible to
• use smaller pole pitches
• use fractional pitch concentrated windings
• use larger air gaps
• position with higher accuracy
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19. Advantages and disadvantages
Advantages of PM machines compared to alternatives:
• more efficient
• higher power density
• higher accuracies
• high speeds
Disadvantages
• limited field weakening
• risk of demagnetisation
• cost?
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20. Structure
1 Permanent magnets
2 Classification of PM machines
3 What is different from other types of machines
4 Calculation methods
5 Issues
6 Conclusions
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21. Calculation methods
• 1D analytical approximations
• 2D analytical modelling
• Numerical: FEM
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22. Analytical machine model
- Magnetic vector potential
- 2 dimensional
- Boundary conditions

 A  
 A  
2
  J s    Br
t
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23. FEM: Range extender
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24. Structure
1 Permanent magnets
2 Classification of PM machines
3 What is different from other types of machines
4 Calculation methods
5 Issues
6 Conclusions
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25. Issues
• Demagnetisation (earlier)
• Losses, mainly for fractional pitch windings
• Availability of magnet material and magnet cost
• Fault tolerance
• Design for specific applications
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26. Availability of NdFeB material
• Between 1990 and 2005, magnet prices dropped by roughly a
factor of 10
• The permanent magnet crisis (2010/2011)
• Over 95% of rare earth materials mined in China
• Large demand
• Renewable energy generation
• Electric mobility
• China protects market
• Long term
• Materials also found at other places
• Mining is being developed
• Cost??
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27. Direct drive generators in wind
turbines
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28. Direct drive: PM and alternatives
Electrical excitation PM excitation
Generator cost (k€) 447 312 > 794
Annual energy yield (GWh) 7.88 8.04
Active material weight (ton) 46 24
NdFeB (€/kg) 25 > 250
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29. Linear PM generator
Archimedes Wave
Swing
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30. Wheel motor
Nuna
• High efficiency
• No gear losses
• 100 km/h @ 2 kW solar
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31. HISPEM: 200 kW, 45000 rpm
• High power density
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32. HISPEM fault tolerant
• 5 or 7 phase
• 75 kW
• 60000 rpm
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33. Conclusions
Main reasons to use PM machines:
• High efficiency
• High force density
Main issues
• Risk of demagnetisation
• Availability of materials and cost
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