• Journal of the Korea Convergence Society
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• v.8 no.5
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• pp.179-184
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• 2017

The cage of a tapered roller bearing keeps the gap between the rollers, which prevents friction, wear and suppresses heating. The material of the cage is changing from metal to plastic for lightening the weight. If the cage is severely deformed due to resonance, the roller may not be able to roll and even get off the cage. In this paper, the dynamic characteristics of the cage is analyzed according to the cage material. Under the assumption that a train runs at the highest speed, frequency harmonics of that speed is calculated, and the comparative analysis is carried out in order to select the optimum thickness of the cage, which is easy to change among the cage design variables for avoiding the resonance.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.367-368
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• 2015

최근에 인도와 유럽을 중심으로 기존의 AC 송전계통 중 일부를 DC 송전계통으로 대체하는 하이브리드형 송전방식에 대한 연구가 진행중이다. 따라서 본 연구는 기존에 연구되고 있는 하이브리드형 가공송전계통을 기반으로 지중송전계통을 포함한 하이브리드형 혼합송전계통이 향후 머지않아 국내에서 계획 및 건설될 것을 대비한 초기 연구로서 진행하였다. 본 논문의 관점은 하이브리드 혼합송전계통 중 지중송전계통구간에서 DC 선로가 AC선로로부터 얼마나 고조파 전압 및 전류 측면에서 영향을 받는가를 평가하고, 이를 근거로 DC 케이블의 배열을 선정하고자 한다. 또한 DC 케이블 배열 선정을 위해 가능성이 있는 여러 개의 CASE별로 구분하고, 가장 타당한다고 평가되는 배열을 제안하고자한다. 본 연구에서 계통 모델링 및 해석은 EMTP를 이용하였다.

• Proceedings of the KAIS Fall Conference
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• 2011.05a
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• pp.73-76
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• 2011

최근 배전계통에 태양광전원의 전력변환장치나 비선형기기에서 발생되는 고조파는 보호계전기의 오동작 및 기기의 손실 등을 초래하여, 이에 대한 전력품질특성 해석이 필수적인 상황이다. 따라서 본 논문에서는 태양광전원이 연계되어 정상운용중인 배전계통에 미치는 전력품질 특성시험을 위하여, LabVIEW를 이용한 전력품질 평가시스템을 제작하였다. 그리고 이 장치를 통해 태양광전원 연계 시 발생하는 고조파특성을 분석하여, 제한한 평가시스템의 유용성을 확인하였다.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.3
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• pp.128-133
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• 1998

This paper is study on performance analysis of modulator using direct digital frequency synthesizer of Initial Clock Accumulating Method. It has been generally used for PLL or digital frequency synthesizing method to be synthesizd randomly chosen frequency state. In order to improve disadvantage of two methods, we constructed modulator system using DDFS of Initial Clock Accumulating Method. We also confirmed the coherence frequency hopping state and possibility of phase control. The results obtained from the experiments are as follows; First, the synthesized output frequency is proportional to the sampling frequency, according to index, K. Second, the difference of the gain between the basic frequency and the harmonic frequencies was more than 50 [dB], that is, this means facts that is reduced the harmonic frequency factor. Third, coherence frequency hopping state is confirmed by PN code sequence. Here, we confirmed the proposed method cut switching time, this verify facts that is the best characteristic of the frequency hopping. We also verified the fact that the phase varies as the adder is operated set or reset.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1324-1325
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• 2011

본 논문은 영구자석을 사용한 풍력발전기의 특성해석 기법에 관한 기초적인 연구로 시뮬레이션 해석기법을 적용하였다. 해석을 위한 발전기 모델은 SPMSG(Surface-Mounted Permanent Magnet Synchronous Generator; 표면 부착형 영구자석 동기발전기)로 선정하였으며 정격출력은 750[kW], 정격회전속도는 25[rpm]rpm의 사양을 가지는 발전기의 특성에 관하여 해석을 수행하였다. 설계 및 해석 과정에서 영구자석의 형상을 주요 변수로 설정하고 자속밀도의 균일한 분포와 풍력 발전기의 정속운전 상태에서 발생하는 전기자 권선의 역기전력 파형을 확인하여 고조파 성분을 저감하는 것에 중점을 두고 특성해석을 수행하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.4
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• pp.22-29
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• 2002

Usually, much harmonics are included and cause harmonic loss of motor, torque pulsation, electro-magnetic noise and shock etc. by switching function of inverter when drive induction motor variableness inside. It applied partial resonant Buck converter and three phase voltage type SPWM inverter circuit to induction motor driving system in this paper that see to solve such problem. Changed operation condition variously to do input current of circuit that propose sine-wave by unit power factor almost and capacitor supplied bringing back to life voltage by power supply arranging properly assistance diode and electric power switching. Power factor and efficiency improved as that minimize variation of input at power supply voltage polarity reverse by that add voltage reversal function. Also, by using output filter, reduced harmonic of output line to line voltage components, and introduce state space analysis and forecast operation of rectifier. Such all items confirmed validity through simulation and an experiment.

• The Journal of Engineering Geology
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• v.14 no.2
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• pp.147-168
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• 2004

Purpose of this study is to quantitatively characterize the fracture roughness which was measured with a confocal laser scanning microscope. The roughness discrete data measured by confocal laser microscope were analyzed by spectral analysis and fast Fourier transform (FFT).The roughness data by used noise reduction filter were applied for fractal analysis to describe roughness features quantitatively. Artificial fractures created by Brazilian test on granites were used to measure fracture roughness under the confocal laser scanning microscope. Measurements were performed along three scan lines on each fracture surface. 36 scan lines were determined on 12 specimens in total. Features of roughness showed that coarse and medium grained granites tend to more rough features than those of fine grained granites. Continuous analog data of roughness is possible to described as discrete data of measure roughness with a fixed interval under the confocal laser microscope. Results of FFT with the measured data showed the highest values on the second harmonics. Distribution of average amplitude of second harmonics was observed 0.9853 in coarse grained granite, 1.0792 in medium grained granite and 0.6794 in fine grained granite. This indicates that the larger roughness has the higher energy of harmonics as the result of fractal analysis in low frequency zone.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.2
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• pp.85-92
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• 1999

The fact that material degradation can be evaluated by measuring nonlinear acoustic effect has been proposed by previous studies. The most conventional method to measure nonlinear acoustic effect is to measure the absolute magnitude of fundamental and $2^{nd}$ order harmonic frequency component in the propagated ultrasonic wave. For this aim, power spectral analysis technique has been used widely. However, the power spectral analysis has fatal disadvantage that the gaussian additive noise superimposed in the wave signal remains in the power spectrum domain. Moreover, the magnitude of $2^{nd}$ order harmonic frequency component generated by nonlinear effect is so small that it may be suppressed by the noise remained in the power spectrum. In order to overcome this problem, this paper proposes an alternative method using bispectrum analysis, which can reduce the effect of addictive gaussian noise and. the nonlinear parameter can be obtained more stably. Simulations showed that the proposed method can obtain the value of nonlinear parameter near to the true value in the case of low SNR signal. Also, in order to confirm the usefulness of our method in actual case, we compared the nonlinear parameter obtained by using both of power spectral and bispectral analysis for several specimen intentionally degraded by fatigue load.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.752-753
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• 2015

본 논문에서는 극-슬롯 조합, 회전자 배리어의 형상에 따른 매입형 영구자석 동기전동기(IPMSM)의 공극자속밀도, 역기전력 특성을 분석하였다. 먼저 유한요소해석(FEM)을 수행하여 공극자속밀도와 역기전력을 추출하였으며, 추출된 데이터를 고속퓨리에변환(FFT)을 이용해 고조파 분석을 수행하였다. 이를 통해 극-슬롯 조합과 회전자 배리어 형상 간의 조합이 공간고조파의 크기에 중요한 영향을 미치는 것을 확인하였다.

• Journal of Institute of Convergence Technology
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• v.10 no.1
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• pp.25-29
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• 2020

Magnetic gears of non-contact power type have great advantages in terms of maintenance and repair than mechanical gears, and are used in various ways. Harmonic gears can derive a higher gear ratio than conventional gears through power transmission through a unique rotation mechanism. Magnetic harmonic gears, in which the gear teeth of the harmonic gears are replaced with magnets, have the advantages of both gears, but are difficult to implement and practical, so many studies are being conducted. In this study, we check whether the results of various types of magnetic gears can be applied to harmonic gears. By applying the axial type magnetic gear to the harmonic gear, the characteristic analysis is conducted to see if the result comparable to the existing radial type magnetic harmonic gear is obtained.