Improved Cogging Calculation Methods for Surface Mounted Permanent Magnet Synchronous Motors

Sooriyakumar, Gunaratnam; Perryman, Roy; Dodds, Stephen J.

doi:10.1109/upec.2006.367580

“…This paper continues the work of earlier research [1] undertaken in developing improved cogging calculation methods for surface mounted permanent magnet synchronous motors (PMSM), with the presentation of comparative experimental results. As part of the design process of PMSMs a combination of analytical calculation and finite element analysis (FEA) was used for cogging torque and air-gap flux density calculations.…”

Section: Introductionmentioning

confidence: 59%

“…The analytical method used in this paper is based on reference [1] which is an extension of the analytical method given in references [2] and [3]. Both methods predict a peak to peak cogging torque of approximately…”

Section: Slot 6 Pole Designmentioning

confidence: 99%

Cogging analysis for fractional slot/pole permanent magnet synchronous motors

Sooriyakumar

¹

,

Perryman

²

,

Dodds

³

2007

2007 42nd International Universities Power Engineering Conference

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Analytical and FEA predictions of cogging torque are compared with experimental results for a range of non-skewed PMSMs of similar size but with slot/pole ratios of 18/8, 12/10 and 30/8 (fractional) together with 30/10 and 18/6 (integer). The two analytical methods and the experimental data show close agreement and predict that stator or rotor skewing would be required to reduce the cogging torque to acceptable levels for the motors with the integer ratios, but the cogging torques for the fractional ratios are sufficiently small to obviate the need for skewing, thereby reducing the manufacturing operations. Finally the 12/10 ratio is recommended since this yields a higher stall torque than the 18/6 or 30/8 ratios. The explanation of this is that the 12/10 ratio enables a higher slot fill to be obtained than the 30/8 ratio. Also the winding overhang can be significantly reduced for the 12-10 design with a segmented stator in contrast with all the other slot pole combinations.

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“…There are three basic ways to analytically predict the cogging torque, a) integration of the lateral forces along the slot sides [1], [4], b) derivative of the air gap co-energy [3], and c) integration of the tangential component of Maxwell stress tensor along a circular contour inside the air gap [5], [6]. Due to its simplicity and reasonable accuracy, the first approach is chosen.…”

Section: A Analytical Expression Of Cogging Torquementioning

confidence: 99%

A New Technique of Cogging Torque Suppression in Direct-Drive Permanent-Magnet Brushless Machines

Fei

¹

,

Luk

²

2010

IEEE Trans. on Ind. Applicat.

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In direct-drive electric propulsion systems, where there is no reduction gear to minimize and absorb the adverse effects due to cogging torque generated by the permanent magnet (PM) machine, minimization of cogging torque generation is of particular importance. In this paper, a novel axial pole pairing method is proposed to minimize cogging torque generation in a special three-phase outer-rotor PM brushless machine, which uses uneven stator poles to enhance back electromotive force (EMF). Analytical formulas of the machine's cogging torque are first derived. The new technique is compared with conventional cogging torque suppression methods by means of analytical models and comprehensive finite element analysis (FEA). The FEA results show that the new method not only achieves effective cogging torque reduction, but also results in improved harmonic content of the back EMF. The validity of the FEA model is verified by experimental results from the prototype machines. Finally, the significance of optimizing both the load-independent machine design techniques and load-dependent driving techniques to achieve overall torque ripple minimization is discussed.  Index Terms-Axial pole pairing, cogging torque, finite element, magnet pole-arc width, permanent magnet brushless machine, stator teeth pairing, stepped rotor skewing.

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“…There are three basic ways to analytically predict the cogging torque, a) integration of the lateral forces along the slot sides [1], [4], b) derivative of the air gap co-energy [3], and c) integration of the tangential component of Maxwell stress tensor along a circular contour inside the air gap [5], [6]. Due to its simplicity and reasonable accuracy, the first approach is chosen.…”

Section: A Analytical Expression Of Cogging Torquementioning

confidence: 99%

A new technique of cogging torque suppression in direct-drive permanent magnet brushless machines

Fei

¹

,

Luk

²

2009

2009 IEEE International Electric Machines and Drives Conference

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In direct-drive electric propulsion systems, where there is no reduction gear to minimize and absorb the adverse effects due to cogging torque generated by the permanent magnet (PM) machine, minimization of cogging torque generation is of particular importance. In this paper, a novel axial pole pairing method is proposed to minimize cogging torque generation in a special three-phase outer-rotor PM brushless machine, which uses uneven stator poles to enhance back electromotive force (EMF). Analytical formulas of the machine's cogging torque are first derived. The new technique is compared with conventional cogging torque suppression methods by means of analytical models and comprehensive finite element analysis (FEA). The FEA results show that the new method not only achieves effective cogging torque reduction, but also results in improved harmonic content of the back EMF. The validity of the FEA model is verified by experimental results from the prototype machines. Finally, the significance of optimizing both the load-independent machine design techniques and load-dependent driving techniques to achieve overall torque ripple minimization is discussed.  Index Terms-Axial pole pairing, cogging torque, finite element, magnet pole-arc width, permanent magnet brushless machine, stator teeth pairing, stepped rotor skewing.

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Improved Cogging Calculation Methods for Surface Mounted Permanent Magnet Synchronous Motors

Cited by 7 publications

References 7 publications

Cogging analysis for fractional slot/pole permanent magnet synchronous motors

Cogging analysis for fractional slot/pole permanent magnet synchronous motors

A New Technique of Cogging Torque Suppression in Direct-Drive Permanent-Magnet Brushless Machines

A new technique of cogging torque suppression in direct-drive permanent magnet brushless machines

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