Technology Designs aspects of PM machines - EMVT
Transcript of Technology Designs aspects of PM machines - EMVT
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TechnologyDesigns aspects of PM machines
Henk Polinder
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Structure
1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions
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What is a permanent magnet?
• Source of magnetomotive force• Makes magnetic field without a current
rmrmm BHB 0
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Permanent magnet BH curves
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Permanent magnets: demagnetization / temperature
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Permanent magnet properties
???1,4-0,55-0,12-10001,4NdFeB
1000,5-0,03-0,02-7501,0SmCo
200,5-0,25-0,05-1301,2Alnico
21012+0,34-0,2-2500,4Ferrite
Cost (€/kg)
ρ
(μΩm)dHcB/dT
(%/K)dBr/dT(%/K)
HcB(kA/m)
Br(T)
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Structure
1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions
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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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Brushed DC
• Iron armature• Disc armature• Hollow rotor
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PM AC motor
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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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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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Rotor layouts
1 surface mounted magnets2 inset magnets3 embedded magnets4 embedded magnets
Embedded: -Flux weakening-Flux concentration
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Concentrated fractional pitch windings
• Reduces cost• Increases losses in back iron
and magnets
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Range extender: concentrated coils, embedded magnets
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Structure
1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions
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Force density
2kN/m5025dF
dggdgggggg FVFlrFrTP 22 2
dgggg F
PlrV
2
2
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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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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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Structure
1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions
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Calculation methods
• 1D analytical approximations• 2D analytical modelling• Numerical: FEM
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Analytical machine model
2s r
AA J Bt
- Magnetic vector potential- 2 dimensional - Boundary conditions
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FEM: Range extender
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Structure
1 Permanent magnets2 Classification of PM machines3 What is different from other types of machines4 Calculation methods5 Issues6 Conclusions
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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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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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Direct drive generators in wind turbines
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Direct drive: PM and alternatives
25 > 250NdFeB (€/kg)
2446Active material weight (ton)
8.047.88Annual energy yield (GWh)
312 > 794447Generator cost (k€)
PM excitationElectrical excitation
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Linear PM generator Archimedes Wave Swing
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Wheel motor Nuna
• High efficiency• No gear losses• 100 km/h @ 2 kW solar
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HISPEM: 200 kW, 45000 rpm
• High power density
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HISPEM fault tolerant• 5 or 7 phase• 75 kW• 60000 rpm
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Conclusions
Main reasons to use PM machines:• High efficiency• High force density
Main issues• Risk of demagnetisation• Availability of materials and cost