• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.423-426
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• 2009

POSTECH Graduate School of Wind Energy is trying to upgrade the PMSG used for Unison U50 to 900 kW class. Intensive optimization efforts are carried out the reduce the axial size and total weight of the generator while increasing the rated output to 900 kW. The generator features 3.32m stator inner radius, 671mm stator length, 84 pole, 25 rated rpm and 31.6kN/$m^2$ shear force density. To reduce the gross weight, the stronger magnetic material is applied with optimal magnet size resulting lowest cogging torque. Also, instead of stator skewing the stator, the magnet position along the circumference is optimized to further reduce the cogging torque. This scheme eliminates the stator skewing procedure and may enhance the productivity. This method also reduces the total harmonic distortion. In this report, upgrade method, no-load line to line voltage and phase voltage, cogging torque, loss calculations and thermal analysis are presented.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.106-114
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• 1998

Cogging torque is often a principal source of vibration and control difficulty in permanent magnet motors, especially at low speeds and loads. For example, reduction of cogging torque is an important specification for DC motors used for electric power stee- ring. This paper examines two motor design techniques, stator tooth notching and rotor pole skewing with magnet pole shaping, for reduction of cogging torque, and the effect of each method on the airgap flux, and the use of the Maxwell stress method and Fourier decomposition to calculate the periodic cogging torque. The analyses show that the cogging torque can be nearly eliminated by the suggested designs, with minimal scacrifice of output torque.

• 신재생에너지
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• 제6권4호
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• pp.41-49
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• 2010

Over the last decade, wind turbine industry has rapidly increased around world. These days many parts of the wind generators are induction generator. But it has some problems such as gearbox failure, rotor excitation and maintenance. Thus many manufacturers are considered permanent magnet synchronous generator named PMSG and direct drive. PMSG uses NdFeB magnet has many the advantage compare with induction generator. In this study, 3MW class outer rotor type PMSG for wind turbine is proposed. The generator features 2.6m stator outer radius, 1200mm stator length, 81 pole pairs, 14 rated rpm, 42kN/$m^2$ shear force density and 94.2% efficiency. Design and analysis generator using FEM program. Then calculate and derivate no load voltage, losses, conductor temperature. To reduce total harmonic distortion and cogging torque, the stator is applied the stator skewing. And to evaluate the designed generator, compare with other generators by active mass per rating torque and torque density.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권2호
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• pp.10-17
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• 2012

This paper presents an improved iron loss model, for the computation of the no load iron loss in the stator core of the in-wheel permanent magnet synchronous motors (PMSM), for the cases of with and without stator skew. 2-D analytical model is used for the computation of tooth and yoke flux densities of the in-wheel PMSM. The no load iron loss computed by the improved iron loss model, for the cases of with and without skew is compared with the finite element method (FEM) and the results show good consistency.

• Journal of Electrical Engineering and Technology
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• 제12권2호
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• pp.718-725
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• 2017

The method of stator segmentation is generally taken to enhance the electromagnetic performance of surface-mounted permanent magnet (SPM) machine and reduce its production cost. Based on the model with single slot, the expressions of cogging torque in machine with uniform or non-uniform segmentations are deduced and the optimal combination is given. Moreover, this paper discusses a structured skewing method and put forward a novel stator structure model to reduce the cogging torque in segmented permanent magnet machine. The model can reduce the cogging torque amplitude by shifting a proper angle of slot-opening. The shifting angle formula for analysis can also be suitable for other permanent machine with segmented stator. Finally the results of finite element simulation are given to prove that the method is effective and feasible.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.443-443
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• 2009

Cogging Torque is induced by the magnetic attraction between the rotor mounted permanent magnet(PM) and the stator teeth. This torque is an unwanted effect causing shaft vibration, noises, metal fatigues and increased stator length. A variety of techniques exist to reduce the cogging torque of PM generator. Even though the cogging torque can be vanished by skewing the stator slots by one slot pitch or rotor magnets, manufacturing cost becomes high due to the complicated structure and increased material costs. This paper introduces a new cogging torque reduction technique for PM generators that adjusts the azimuthal positions of the magnets along the circumference. A 900 kW class PMSG model is simulated using a three dimensional finite element method and the resulting cogging torques is analyzed using the Maxwell tensor stress tensor. Using the 3D simulation, the end contribution of the cogging torque is accurately calculated.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권1호
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• pp.54-60
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• 2012

In this paper, a new permanent-magnet (PM) linear motor is proposed, in which both the magnets and armature windings are placed in the short mover, while the long stator consists of iron core only. Hence, this new PM linear motor can be called a primary permanent-magnet linear motor. It exhibits the advantages of robustness, low cost, high efficiency, high power factor, and high thrust force density. It is especially suitable for long stator applications such as urban rail transit. In this paper, the topology and operation principle of this motor are discussed in detail. The steady-state characteristics including field distributions, flux-linkage, back-EMF, phase inductance and thrust force are investigated. In addition, the technique of skewing stator teeth is adopted to improve the electromagnetic performance. Results from finite element method (FEM) verified the theoretical analysis results.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권9호
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• pp.437-442
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• 2006

Cogging torque, the primary ripple component in the torque generated by permanent magnet (PM) motors, is due to the slotting on the stator or rotor. This article shows the reduction of cogging torque in a novel axial flux permanent magnet (AFPM) motor through the various design schemes. 3D finite element method is used for the exact magnetic field analysis. The effects of slot shapes and skewing of slot on the cogging torque and the average torque have been investigated in detail.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권3호
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• pp.123-130
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• 2006

This paper presents characteristics analysis of skewed Synchronous Reluctance Motor using equivalent magnetic circuit and compares with the result of Finite Element Method. Torque ripple must be reduced, because it is producing noise and vibration. There is many kinds of method to reduce torque ripple, but generally we apply skewing stator or rotor. The 2D Finite Element Method(FEM) or 3D FEM is used to analyze the motor, since skew influence the average torque in the motor. However, the FEM takes much time in spite of the advanced computer and numerical technique. This paper will analyze characteristics of skewed synchronous reluctance motor using equivalent magnetic circuit.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.1180-1182
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• 2005

In this paper, the design and field analysis of the novel axial flux type permanent magnet(AFPM) motor with double stator and single rotor are investigated. The various design schemes of AFPM based on 3D finite element method are proposed. The effects of slot shapes, various magnetization of PM, and skewing on the cogging torque and average torque have been investigated in detail. From the results, we can improve the cogging torque and average torque characteristics.