Technology Designs aspects of PM machines

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Henk Polinder

Technology
Designs aspects of PM (Permanent Magnet) machines

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Technology Designs aspects of PM machines

  1. 1. TechnologyDesigns aspects of PM machinesHenk Polinder Challenge the future 1
  2. 2. Structure1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions Challenge the future 2
  3. 3. What is a permanent magnet?• Source of magnetomotive force• Makes magnetic field without a currentBm   0  rm H m  Br Challenge the future 3
  4. 4. Permanent magnet BH curves Challenge the future 4
  5. 5. Permanent magnets: demagnetization / temperature Challenge the future 5
  6. 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 2Alnico 1,2 -130 -0,05 -0,25 0,5 20SmCo 1,0 -750 -0,02 -0,03 0,5 100NdFeB 1,4 -1000 -0,12 -0,55 1,4 ??? Challenge the future 6
  7. 7. Structure1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions Challenge the future 7
  8. 8. Classification• DC mechanical commutator • Iron armature • Hollow rotor • Disc armature• AC electronic commutation PMSM / Brushless DC • Surface mounted / embedded magnets • Distributed / concentrated windings Challenge the future 8
  9. 9. Brushed DC• Iron armature• Disc armature• Hollow rotor Challenge the future 9
  10. 10. PM AC motor Challenge the future 10
  11. 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 Challenge the future 11
  12. 12. PMSM or BDCMPMSM:- distributed windings- sinusoidal voltage- sinusoidal currents- continuous position sensor- smooth forceBDCM:- concentrated windings- trapezoidal voltage- rectangular currents- 6 step position sensor- force ripple Challenge the future 12
  13. 13. Rotor layouts1 surface mounted magnets2 inset magnets3 embedded magnets4 embedded magnetsEmbedded:-Flux weakening-Flux concentration Challenge the future 13
  14. 14. Concentrated fractional pitch windings• Reduces cost• Increases losses in back iron and magnets Challenge the future 14
  15. 15. Range extender: concentrated coils, embedded magnets Challenge the future 15
  16. 16. Structure1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions Challenge the future 16
  17. 17. Force densityP   g T   g rg F  2 g rg2l g Fd  2 gVg FdFd  25  50 kN/m 2 PVg  r l  2 2 g Fd g g Challenge the future 17
  18. 18. Differences with other machinesPermanent magnets make it possible to• use smaller pole pitches• use fractional pitch concentrated windings• use larger air gaps• position with higher accuracy Challenge the future 18
  19. 19. Advantages and disadvantagesAdvantages of PM machines compared to alternatives:• more efficient• higher power density• higher accuracies• high speedsDisadvantages• limited field weakening• risk of demagnetisation• cost? Challenge the future 19
  20. 20. Structure1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions Challenge the future 20
  21. 21. Calculation methods• 1D analytical approximations• 2D analytical modelling• Numerical: FEM Challenge the future 21
  22. 22. Analytical machine model- Magnetic vector potential- 2 dimensional- Boundary conditions   A   A   2   J s    Br t Challenge the future 22
  23. 23. FEM: Range extender Challenge the future 23
  24. 24. Structure1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions Challenge the future 24
  25. 25. Issues• Demagnetisation (earlier)• Losses, mainly for fractional pitch windings• Availability of magnet material and magnet cost• Fault tolerance• Design for specific applications Challenge the future 25
  26. 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?? Challenge the future 26
  27. 27. Direct drive generators in wind turbines Challenge the future 27
  28. 28. Direct drive: PM and alternatives Electrical excitation PM excitationGenerator cost (k€) 447 312 > 794Annual energy yield (GWh) 7.88 8.04Active material weight (ton) 46 24NdFeB (€/kg) 25 > 250 Challenge the future 28
  29. 29. Linear PM generator Archimedes Wave Swing Challenge the future 29
  30. 30. Wheel motor Nuna• High efficiency• No gear losses• 100 km/h @ 2 kW solar Challenge the future 30
  31. 31. HISPEM: 200 kW, 45000 rpm• High power density Challenge the future 31
  32. 32. HISPEM fault tolerant• 5 or 7 phase• 75 kW• 60000 rpm Challenge the future 32
  33. 33. ConclusionsMain reasons to use PM machines:• High efficiency• High force densityMain issues• Risk of demagnetisation• Availability of materials and cost Challenge the future 33

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