Henk Polinder Technology Designs aspects of PM (Permanent Magnet) machines

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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