1 Florence Libert NORPIE 2004 Design Study of Different Direct-Driven Permanent–Magnet Motors for a Low Speed Application

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Florence LibertNORPIE 2004

Design Study of Different Direct-Driven

Permanent–Magnet Motors

for a Low Speed Application

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The goal of the study is to compare different designs of direct-driven permanent magnet (PM) motors that should replace an induction motor and its gearbox for an industrial application requiring 5 kW and 50 rpm.

Low Speed PM Drives

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Content

• The investigated rotor configurations

• Advantages and drawbacks of the investigated configurations

• The design procedure

• Results and comparisons

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The investigated rotor configurations

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Rotors with surface-mounted PM

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Rotors with buried PM

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Advantages and drawbacks of the investigated configurations• For buried PM:

» Flux concentration» Protection of the magnets» Reluctance torque

• Drawbacks: » Many magnets for V-shape PM» Many pieces for Tangential PM

rotor giving production difficulties

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Design procedure followed for a low speed PM motor

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Phasor diagram

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Result and comparison

• Torque ripple

• Weight and choice of the pole number

• Chosen designs

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Active weight as a function of the pole numbers for different PM motor designs

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Fundamental of flux density in the airgap B and length for different configurations and

p=50

SMPMOuter rotor

SMPMInset PM

Tangentially magnetized

PM

B [T] 0.911 0.857 0.906 1.12

Length

[mm]191 179 199 144

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Ratio between the torque ripple and the mean torque

SMPMOuter rotor

SMPMInset PM


PM

p=30 0.16 0.48 0.30 0.49

p=50 0.14 0.40 0.35 0.40

p=68 0.20 0.58 0.24 0.59

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Geometries of 60-pole outer rotor PM and

tangentially magnetized PM optimal designs

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Comparison between outer rotor design and buried magnet design for p=60

Outer rotorSMPM


PM

Total active weight [kg] 87.1 80.1

Magnet weight [kg] 5.5 5.5

Length [mm] 189 154

Fundamental of airgap flux density B [T] 0.838 1.1

Mean torque [p.u] 0.993 0.997

Efficiency [%] 81.6 82.4

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Conclusion

• Rotor with V-shape magnets is not appropriate for designs with high pole numbers

• Outer rotor designs are lighter than inner rotor designs

• Inset PM motors are slightly lighter than SMPM thanks to the reluctance torque

• High torque ripple when q=1 demands to consider other winding configurations

• Tangentially magnetized PM designs are the lightest due to the flux concentration

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Conclusion

• It is possible to design direct-driven PM motors with better efficiency and less weight than the induction motor and its gearbox

• A prototype is required to confirm experimentally the results

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Thank youfor your attention

Documents

1 Florence Libert NORPIE 2004 Design Study of Different Direct-Driven Permanent–Magnet Motors for a Low Speed Application