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  • 1. TechnologyDesigns aspects of PM machinesHenk Polinder Challenge the future 1
  • 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. 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. Permanent magnet BH curves Challenge the future 4
  • 5. Permanent magnets: demagnetization / temperature Challenge the future 5
  • 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. Structure1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions Challenge the future 7
  • 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. Brushed DC• Iron armature• Disc armature• Hollow rotor Challenge the future 9
  • 10. PM AC motor Challenge the future 10
  • 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. 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. Rotor layouts1 surface mounted magnets2 inset magnets3 embedded magnets4 embedded magnetsEmbedded:-Flux weakening-Flux concentration Challenge the future 13
  • 14. Concentrated fractional pitch windings• Reduces cost• Increases losses in back iron and magnets Challenge the future 14
  • 15. Range extender: concentrated coils, embedded magnets Challenge the future 15
  • 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. 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. 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. 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. Structure1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions Challenge the future 20
  • 21. Calculation methods• 1D analytical approximations• 2D analytical modelling• Numerical: FEM Challenge the future 21
  • 22. Analytical machine model- Magnetic vector potential- 2 dimensional- Boundary conditions   A   A   2   J s    Br t Challenge the future 22
  • 23. FEM: Range extender Challenge the future 23
  • 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. 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. 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. Direct drive generators in wind turbines Challenge the future 27
  • 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. Linear PM generator Archimedes Wave Swing Challenge the future 29
  • 30. Wheel motor Nuna• High efficiency• No gear losses• 100 km/h @ 2 kW solar Challenge the future 30
  • 31. HISPEM: 200 kW, 45000 rpm• High power density Challenge the future 31
  • 32. HISPEM fault tolerant• 5 or 7 phase• 75 kW• 60000 rpm Challenge the future 32
  • 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