Influence of Slot Openings and Tooth Profile on Cogging Torque in Axial-Flux PM Machines

Slotted axial-flux machines have excellent power and torque densities. However, it is difficult to reduce their cogging torque due to the complexity associated with implementing classical techniques. In this paper, slot-opening widths and tooth profiles will be shown to be significant in mitigating cogging torque in these machines. In particular, varying the slot opening reduced it by 52%, whereas a parallel-tooth (rectangular) profile lowered it by 24%, when compared with a conventional trapezoidal-tooth profile. An analytical quasi-3-D analysis was formulated and used to analyze and determine cogging torque. It was validated numerically and experimentally. Its versatility is in its ability to analyze different shapes of poles and slot openings, which can be extended to model air-gap nonuniformity. This paper also presents cogging torque minimization techniques that maintain the ease of manufacture of the parallel-tooth stator. Experimental results showed 73% and 48% reduction in cogging torque, which are achieved by the use of alternating pole arcs and skewed poles.

[1]  J. Soulard,et al.  Investigation on Pole-Slot Combinations for Permanent-Magnet Machines with Concentrated , 2004 .

[2]  E. Semail,et al.  Slot/pole combinations choice for concentrated multiphase machines dedicated to mild-hybrid applications , 2011, IECON 2011 - 37th Annual Conference of the IEEE Industrial Electronics Society.

[3]  Thomas A. Lipo,et al.  Torque quality and comparison of internal and external rotor axial flux surface-magnet disc machines , 2006, IEEE Transactions on Industrial Electronics.

[4]  Ronghai Qu,et al.  Effect of unbalanced and inclined air-gap in double-stator inner-rotor axial flux permanent magnet machine , 2014, 2014 International Conference on Electrical Machines (ICEM).

[5]  G. Barakat,et al.  Influence of skewing on the performances of an axial flux PM wind generator coupled to a diode rectifier , 2007, 2007 IEEE International Electric Machines & Drives Conference.

[6]  Z.Q. Zhu,et al.  Comparison of alternate analytical models for predicting cogging torque in surface-mounted permanent magnet machines , 2008, 2008 IEEE Vehicle Power and Propulsion Conference.

[7]  P. Barendse,et al.  A simple core structure for small axial-flux PMSGs , 2011, 2011 IEEE International Electric Machines & Drives Conference (IEMDC).

[8]  J.A. Tapia,et al.  Design Consideration to Reduce Cogging Torque in Axial Flux Permanent-Magnet Machines , 2007, IEEE Transactions on Magnetics.

[9]  P.C.K. Luk,et al.  Cogging torque reduction techniques for axial-flux surface-mounted permanent-magnet segmented-armature-torus machines , 2008, 2008 IEEE International Symposium on Industrial Electronics.

[10]  F. Crescimbini,et al.  Experimental study on reducing cogging torque and core power loss in axial-flux permanent-magnet machines with slotted winding , 2002, Conference Record of the 2002 IEEE Industry Applications Conference. 37th IAS Annual Meeting (Cat. No.02CH37344).

[11]  Thomas A. Lipo,et al.  Design, Analysis, and Control of a Hybrid Field-Controlled Axial-Flux Permanent-Magnet Motor , 2010, IEEE Transactions on Industrial Electronics.

[12]  J. Poza,et al.  Axial-Flux-Machine Modeling With the Combination of FEM-2-D and Analytical Tools , 2012, IEEE Transactions on Industry Applications.

[13]  F. Crescimbini,et al.  Experimental study on reducing cogging torque and core power loss in axial-flux permanent-magnet machines with slotted winding , 2002 .

[14]  J. Pyrhönen,et al.  TORQUE RIPPLE OF PERMANENT MAGNET MACHINES WITH CONCENTRATED WINDINGS , 2005 .

[15]  Min-Fu Hsieh,et al.  Cogging torque reduction in axial flux machines for small wind turbines , 2009, 2009 35th Annual Conference of IEEE Industrial Electronics.

[16]  J. Pyrhonen,et al.  Modeling of axial flux permanent-magnet machines , 2004, IEEE Transactions on Industry Applications.

[17]  M. Aydin,et al.  Magnet skew in cogging torque minimization of axial gap permanent magnet motors , 2008, 2008 18th International Conference on Electrical Machines.

[18]  Thomas M. Jahns,et al.  Pulsating torque minimization techniques for permanent magnet AC motor drives-a review , 1996, IEEE Trans. Ind. Electron..

[19]  Mingyao Lin,et al.  Rotor design techniques for reducing the cogging torque in a novel dual-rotor axial field flux-switching permanent magnet machine , 2014, 2014 17th International Conference on Electrical Machines and Systems (ICEMS).

[20]  Sang-Moon Hwang,et al.  Minimization of cogging torque in permanent magnet motors by teeth pairing and magnet arc design using genetic algorithm , 2001 .

[21]  M.A. Valenzuela,et al.  Cogging Torque Reduction in an Axial Flux PM Machine via Stator Slot Displacement and Skewing , 2007, IEEE Transactions on Industry Applications.

[22]  Z.Q. Zhu,et al.  Analytical Methods for Minimizing Cogging Torque in Permanent-Magnet Machines , 2009, IEEE Transactions on Magnetics.

[23]  Thomas A. Lipo,et al.  Cogging torque minimization technique for multiple-rotor, axial-flux, surface-mounted-PM motors: alternating magnet pole-arcs in facing rotors , 2003, 38th IAS Annual Meeting on Conference Record of the Industry Applications Conference, 2003..

[24]  Yacine Amara,et al.  A New Quasi-3-D Analytical Model of Axial Flux Permanent Magnet Machines , 2014, IEEE Transactions on Magnetics.

[25]  G. Barakat,et al.  Quasi-3-D analytical modeling of the magnetic field of an axial flux permanent-magnet synchronous machine , 2005, IEEE Transactions on Energy Conversion.

[26]  F. Caricchi,et al.  Recent Advances in Axial-Flux Permanent-Magnet Machine Technology , 2012, IEEE Transactions on Industry Applications.

[27]  M.A. Khan,et al.  Prototyping a Composite SMC/Steel Axial-flux PM Wind Generator , 2006, Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting.

[28]  Peter Sergeant,et al.  Optimized Design Considering the Mass Influence of an Axial Flux Permanent-Magnet Synchronous Generator With Concentrated Pole Windings , 2010, IEEE Transactions on Magnetics.

[29]  Chang-Chou Hwang,et al.  Optimization for Reduction of Torque Ripple in an Axial Flux Permanent Magnet Machine , 2009, IEEE Transactions on Magnetics.

[30]  Metin Aydin,et al.  Reduction of Cogging Torque in Double-Rotor Axial-Flux Permanent-Magnet Disk Motors: A Review of Cost-Effective Magnet-Skewing Techniques With Experimental Verification , 2014, IEEE Transactions on Industrial Electronics.

[31]  Matteo Felice Iacchetti,et al.  Effects of Manufacturing Imperfections in Concentrated Coil Axial Flux PM Machines: Evaluation and Tests , 2014, IEEE Transactions on Industrial Electronics.

[32]  Z.Q. Zhu,et al.  Minimization of Cogging Torque in Axial-Flux Permanent-Magnet Machines: Design Concepts , 2007, IEEE Transactions on Magnetics.

[33]  Matteo Felice Iacchetti,et al.  Axial Flux PM Machines With Concentrated Armature Windings: Design Analysis and Test Validation of Wind Energy Generators , 2011, IEEE Transactions on Industrial Electronics.

[34]  Fabio Giulii Capponi,et al.  On the Use of Magnetic Wedges in Axial Flux Permanent Magnet Machines , 2013, IEEE Transactions on Industrial Electronics.

[35]  Jian Li,et al.  Minimization of Cogging Torque in Fractional-Slot Axial Flux Permanent Magnet Synchronous Machine with Conventional Structure , 2012, 2012 Sixth International Conference on Electromagnetic Field Problems and Applications.

[36]  Kan Akatsu,et al.  Suppressing Pulsating Torques: Torque Ripple Control for Synchronous Motors , 2014, IEEE Industry Applications Magazine.

[37]  Fabrizio Marignetti,et al.  An Online Method for Static Eccentricity Fault Detection in Axial Flux Machines , 2015, IEEE Transactions on Industrial Electronics.

[38]  R. Wallace,et al.  Cogging torque reduction in an axial flux PM machine with extended speed range , 2005, IEEE International Conference on Electric Machines and Drives, 2005..