Analysis of Flux Leakage in a Segmented Core Brushless Permanent Magnet Motor

							Analysis of Flux Leakage in a Segmented
                   Core
 Brushless Permanent Magnet Motor




                                          1
                  OVERVIEW
•   INTRODUCTION
•   SEGMENTED CORE TECHNOLOGY
•   MAGNETIC EQUIVALENT NETWORK (MEN) FOR SEGMENTED
    CORE MOTORS
•   REDUCED MODEL OF MEN
•   FLUX LEAKAGE PARAMETER α
•   EFFECTS OF DESIGN PARAMETERS ON α
•   CONCLUSION
•   REFERENCES



                                                  2
               INTRODUCTION

• Brushless Permanent Magnet (BPM) motors
• Highly Popular
              High efficiency
              Precise control
              Large speed operation
              Compactness.




                                            3
SEGMENTED CORE CONSTRUCTION
         Better utilization of coil space
         Higher efficiency
         High torque density




 Fig. 1. Linearized motor topology
                                            4
MAGNETIC EQUIVALENT NETWORK FOR
    SEGMENTED CORE MOTORS




   Fig. 2. Magnetic equivalent network
                                         5
                  PARAMETERS USED
• φr /2 - Flux source of one-half of the magnetic pole.
• φg /2 -Air-gap flux that passes through one-half of the airgap.
• 2Rmo and 2Rg are the reluctances to fluxes φr /2 and φg /2
  respectively.
• Rgj - Reluctance of the air gap at the joint between two stator
  segments.
• Rml - Reluctance due to magnet-end flux leakage of a pole.
• Rmm - Reluctance due to magnet pole-to-pole leakage.
• Rtp - Reluctance for the leakage flux between adjacent tooth
  tips.


                                                                    6
REDUCED MODEL OF MEN




Fig. 3. MEN reduced from Fig. 2.



                                   7
FLUX LEAKAGE PARAMETER α
From fig.3 using the equivalent-resistance theory




Air gap flux produced by one half of the pole




4RSS is the parallel combination of Rgj and Rtp




              Where
                                                    8
                        Contd..
Tooth-tip leakage flux




φtp and φr can again be expressed as




Btp is the flux density at tooth tip
Br and Am are the remanent flux
density and flux surface area of the magnet pole

                                                  9
                     Contd..


Rg ,Rgj , and Rm - property-dependent functions.




gc is the air gap between a stator and rotor
air-gap area Ag ≈ Am.




wsb is the stator back iron thickness and
gj is the gap of air between segments              10
                        Contd..


Rmm is the magnet-to-magnet leakage reluctances
Rmm = ∞ and Rm ≈ Rmo .




Substituting these values in eq (4)




                                                  11
Am ≈ τm L,

where τm is the width of the magnet pole at the surface




                                                          (10)




                                                                 12
EFFECTS OF DESIGN PARAMETERS ON α




  Fig. 4. Plot of α versus lm /(µr g)


                                        13
                            Contd…




Fig. 5. Plot of α versus Br /B0

                                     14
                                   Contd…




Fig. 6. Plot of α versus τm /htp


                                            15
                             Contd..




Fig. 7. Plot of α versus gj /g

                                       16
                               Contd..




Fig. 8. Plot of α versus wso /gj

                                         17
           FLUX CONTOUR PROFILE




Fig. 9. motor with solid laminations.   Fig. 10. motor with segmented core.



                                                                              18
                   CONCLUSION
• α – expressed as a function of magnetic material properties
  and motor dimensions.

• Various parameters on α have also been studied

• Analysis can be used to design a segmented-stator motor with
  improved efficiency




                                                                19
                           REFERENCES

[1] M. Faizul Momen, and Susanta Datta, “Analysis of Flux Leakage in a
    Segmented Core Brushless Permanent Magnet Motor”. IEEE Transactions
    on energy conversion, volume 24, no. 1, march 2009
[2] Z. Q. Zhu, D. Howe, and C. C. Chan, “Improved analytical model for
    predicting the magnetic field distribution in brushless permanent-magnet
    machines,” IEEE Transactions on Magnetics, volume38, no. 1, pp. 229–238,
    January 2002.
[3] C. Hwang and Y. H. Cho, “Effects of leakage flux on magnetic fields
    of interior permanent magnet synchronous motors,” IEEE Transactions on
    Magnetics,volume 37, no. 4, pp. 3021–3024, July 2001.
 [4] W. B. Tsai and T.-Y. Chang, “Analysis of flux leakage in brushless permanent
    magnet motor with embedded mangnets,” IEEE Transactions on
    Magnetics,volume 35, no.1, pp. 543–547, January 1999.


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