Technology Designs aspects of PM machines
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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.
Technology Designs aspects of PM machines
- 1. Technology Designs aspects of PM machines Henk Polinder Challenge the future 1
- 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 Challenge the future 2
- 3. What is a permanent magnet? • Source of magnetomotive force • Makes magnetic field without a current Bm 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 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 ??? Challenge the future 6
- 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 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 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 Challenge the future 12
- 13. Rotor layouts 1 surface mounted magnets 2 inset magnets 3 embedded magnets 4 embedded magnets Embedded: -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. 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 Challenge the future 16
- 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 Challenge the future 17
- 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 Challenge the future 18
- 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? Challenge the future 19
- 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 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. 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 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 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 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. Conclusions Main reasons to use PM machines: • High efficiency • High force density Main issues • Risk of demagnetisation • Availability of materials and cost Challenge the future 33