• 조명전기설비학회논문지
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• 제28권4호
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• pp.49-55
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• 2014

In this paper, we propose the cogging toque reduction technique of the dual stator radial flux permanent magnet generator. The cogging toque is caused by the torque ripple increase and vibration and noise of the generator. And it is important factor determining cut-in speed of the small wind generator. To reduce cogging torque, permanent magnet displacement was studied. And the theory of the permanent magnet displacement was formulated and the cogging torque reduction according to the permanent magnet displacement was confirmed through the finite element method.

• Journal of Magnetics
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• 제16권3호
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• pp.281-287
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• 2011

The stationary discontinuous armatures that are used in permanent magnet linear synchronous motors (PM-LSMs) have been proposed as a driving source for transportation systems. However, the stationary discontinuous armature PM-LSM contains the outlet edges which always exist as a result of the discontinuous arrangement of the armature. For this reason, the high alteration of the outlet edge cogging force produced between the armature's core and the mover's permanent magnet when a mover passes the boundary between the armature's installation part and non-installation part has been indicated as a problem. Therefore, we have examined the outlet edge cogging force by installing the auxiliary teeth at the armature's outlet edge in order to minimize the outlet edge cogging force generated when the armature is arranged discontinuously. Moreover, we obtained the calculation by analyzing the shape of the auxiliary teeth in which the outlet edge cogging force is minimized the most.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제11B권2호
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• pp.1-8
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• 2001

This paper deals with magnetic field analysis and computation of cogging torque using an analytical method in Interior Permanent Magnet Motor (IPMM). The magnetic field is analyzed by solving space harmonics field analysis due to magnetizing and the cogging torque is analyzed by combining field analysis with relative permeance. In reducing cogging torque, the inferences of various design variable and magnetizing distribution are investigated. It is shown that the slot and pole ratio (the pole-arc / pole-pitch ratio) combination has a significant effect on the cogging torque and presents a optimal flux barrier shape to reduce the cogging torque. The validity of the proposed technique is confirmed with 2-D Finite Element(FE) analysis.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권9호
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• pp.454-459
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• 2003

Conventional integral-slot design in permanent magnet(PM) motor tends to have a high cogging torque and large end turns, which contribute to copper losses. The fractional-slot design is effective compared to integral-slot design in the cogging torque and electromotive force(EMF) waveform. The effectiveness of fractional slot can be maximized by selecting optimal pole to slot ratio. This paper presents the effect of pole to slot ratio on the cogging torque and EMF waveform in the PM motor with fractional-slot. The effectiveness of the proposed designs has been confirmed by comparing waveform of EMF. cogging torque and torque ripple between conventional and new models.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1031-1032
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• 2007

In order to reduce the cogging torque, by predicting the variation of the cogging torque according to pole arc/pitch ratio by analytical and FE methods, pole arc/pitch ratio which makes the cogging torque minimum are determined. And then, the measurements of cogging torque for permanent magnet generators with determined pole arc/pitch ratio are presented. The reasons for the error between predicted and measured value are discussed fully in terms of the shape of permanent magnet. Finally, by confirming that predicted results for cogging torque according to pole arc/pitch ratio and skew are shown in good agreement with those obtained from measured one, the validation of analysis results is confirmed.

• 전기학회논문지
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• 제66권11호
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• pp.1568-1574
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• 2017

This paper studied cogging torque reduction effect for sloping notch applied two notches on stator teeth. We have confirmed accuracy of FEM(Finite Element Method) through comparison previous model using asymmetric notch for experiment and 3D FEM results, and then cogging torque comparison of previous model and sloping notch model. Also the sloping notch model has been modified to step-sloping notch model to consider manufactur. The modification method of sloping notch changed the degree of slope of notch (a)(Notch(a) sloping Deg) and the degree of Slope of notch (b)(Notch(b) Sloping Deg). When Cogging torque is case of minimum, Notch (a) Sloping Deg is $-12[^{\circ}]$ and Notch(b) Sloping Deg $12[^{\circ}]$. In this case, cogging torque was about 23.9[mNm]. Cogging torque of previous model is about 40.8[mNm], so sloping notch model is less than previous model by 41.42[%]. Also, if sloping notch model is changed to step-sloping notch model, cogging torque of step-sloping notch model is about 24.82[mNm], Therefore the difference between the two cogging torque is about 3.85[%], so step-sloping notch model can be applied when considering manufacture.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권11호
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• pp.547-554
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• 2006

The detent force of a permanent magnet linear motor(PMLM) consists of the end force and cogging force, and should be reduced for high precision purpose applications. The cogging force comes from the electromagnetic interaction between the permanent magnets and interior teeth(or the slots) of the stator, and of which the magnitude depends on the ratio of the numbers of the armature and permanent magnet poles as well as the geometrical shape of the permanent magnet and armature pole. In order to reduce the cogging force of a PMLM, this paper proposes a new configuration which has 9 permanent magnet poles and 10 armature winding slots. By theoretical investigation of the principle of cogging force generation and simulating using finite element method, the proposed PMLM configuration is proven to give much less cogging force than the conventional configuration which has 8 permanent magnet poles and 12 armature winding slots. A proper winding algorithm, modified (A, A, A) winding method, for the proposed configuration is also suggested when the proposed PMLM is operating as a 3 phase synchronous machine. A theoretical and numerical calculation shows that the proposed configuration makes slightly bigger back-emf and thrust force under same exciting current and total number of winding turns condition.

• 전기학회논문지
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• 제61권12호
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• pp.1820-1827
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• 2012

This paper is to present a new method of cogging torque reduction for axial flux PM machines of multiple rotor surface mounted magnets. In order to start softly and to run a power generator even the case of weak wind power, reduction of cogging torque is one of the most important issues for a small wind turbine, Cogging torque is an inherent characteristic of PM machines and is caused by the geometry shape of the machine. Several methods have been already applied for reducing the cogging torque of conventional radial flux PM machines. Even though some of these techniques can be also applied to axial flux machines, manufacturing cost is especially higher due to the unique construction of the axial flux machine stator. Consequently, a simpler and low cost method is proposed to apply on axial flux PM machines. This new method is actually applied to a generator of 1.0kW, 16-poles axial flux surface magnet disc type machine with double-rotor-single-stator for small wind turbine. Design optimization of the adjacent magnet pole-arc which results in minimum cogging torque as well as assessment of the effect on the maximum available torque using 3D Finite Element Analysis (FEA) is investigated in this design. Although the design improvement is intended for small wind turbines, it is also applicable to larger wind turbines.

• Journal of Electrical Engineering and Technology
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• 제11권4호
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• pp.878-888
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• 2016

Cogging torque has a negative impact on the operation of permanent magnet machines by increasing torque ripple, speed ripple, acoustic noise and vibration. In this paper Magnet Shifting Method has been used as a tool to reduce the cogging torque in inset Line Start Permanent Magnet Synchronous Motor (LSPMSM). It has been shown that Magnet Shifting Method can effectively eliminate several lower-order harmonics of cogging torque. In order to implement the method, first the expression of cogging torque is studied based on the Fourier analysis. An analytical expression is then introduced based on Permanent Magnet Shifting to reduce cogging torque of LSPMS motors. The method is applied to some existing machine designs and their performances are obtained using Finite Element Analysis (FEA). The effect of magnet shifting on pole mmf (magneto motive force) distribution in air gap is discussed. The side effects of magnet shifting on back-EMF, core losses and torque profile distortion are taken into account in this investigation. Finally the experimental results on two prototypes 24 slot 4 pole inset LSPMS motors have been used to validate the theoretical analysis.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.67-70
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• 2008

This paper deals with the effect of radial parameters in cogging process such as reduction in height (Rh) and rotational angle ($\theta$) of a billet on a void closure for large forged products. Usually closing and consolidation of internal void defects in a ingot is a vital matter when utilized as large forged products, using a press with limited capacity and the sizes of the ingots becoming larger. Consequently, it is important to develop cogging process for improvement of internal soundness without a void defect and cost reduction by solid forging alone with limited press capacity. For experiments of cogging process, hydraulic press with a capacity of 800 ton was used together with a small manipulator which was made for rotation and overlapping of a billet. Size of a void was categorized into two types; $\emptyset$ 6.0 mm and $\emptyset$ 9.0 mm to investigate the change of closing and consolidation of void defects existed in the large ingot during the cogging process. Also open void and closed void in the ingot were tackled to show the differentiation of closing process of internal voids with respect to void sizes. In this paper systematic configuration for closing process of void defects were expressed based on this experiment results in the cogging process.