• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1128-1129
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• 2007

본 논문은 3상 불평형 전압이 부하에 인가될 때 선간 전압의 실효값을 측정해서 불평형을 검출하고 불평형이 발생되면 선간전압의 실효값이 평형이 되도록 각 상의 상전압을 전력소자를 사용한 위상 각제어를 통해서 각 상별 스위칭각을 비대칭적으로 조절함으로서 3상 전압 불평형 개선하고자 한다. 이를 모의 실험을 통해 유도전동기 부하에서 검증하였고 이를 통한 고조파 영향을 분석하였다.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.46-49
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• 1995

This paper deals with characteristics of magnet that the levitation and guidance forces at static state and we tested and evaluated its. Also we compared to effect of levitation force with material and shape of guide way, focus on evaluation and method of test for the magnet of Urban Transit Maglev vehicle.

• Proceedings of the Membrane Society of Korea Conference
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• 1998.10a
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• pp.91-92
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• 1998

1. 서론 : 고분자를 소재로 하는 중공사막의 제막은 일반적으로 상전환법(phase inversion method)에 의하여 제조된다. 이 방법에 의한 비대칭막의 생성은 용매가 고분자용액을 빠져나가는 속도와 응결액이 고분자쪽으로 침투되는 속도의 차이에 의해서 막의 1차구조가 형성된다. 그러므로 이 속도를 첨가제 등을 사용하여 조절하므로서 막의 특성을 변화시킬 수 있다. 본 연구에서는 polyetherimide(PEI) 중공사막의 첨가제로서 dioxane 등 9종류를 사용하여 중공사막의 생성 구조에 미치는 영향을 검토하였다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.109-110
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• 2016

영구자석 동기 전동기(PMSM)의 결선방법에 따라 전동기의 전압과 전류는 그 크기와 위상에 차이가 발생한다. 따라서, 결선을 고려한 영구자석 동기 전동기의 제어가 필요하다. 본 논문에서는 와이 결선과 델타 결선된 전동기의 등가회로를 모델링하고, 델타 결선된 영구자석 동기 전동기의 구동 시스템에서 직류단 션트저항을 이용한 3상 전류 추정 알고리즘을 제안하였다. 컴퓨터 시뮬레이션을 통해 제안한 알고리즘의 타당성을 검증하였다.

• Journal of the Korean Ceramic Society
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• v.49 no.3
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• pp.253-259
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• 2012

In this study, crystal structural changes and dielectric properties of $(1-x)Pb(Yb_{1/2}Nb_{1/2})O_3-xPbTiO_3$ ((1-x)PYN-xPT) solid solutions were measured and analyzed with respect to the $PbTiO_3$ (PT) contents ($0.40{\leq}x{\leq}0.60$). From X-ray diffraction (XRD) measurements, (1-x)PYN-xPT solid solutions showed changes of the crystal structure from pseudocubic ($0.40{\leq}x{\leq}0.44$) to tetragonal ($0.52{\leq}x{\leq}0.60$) on increasing PT contents and exhibited the coexistence of pseudocubic and tetragonal phase near the morphotropic phase boundary (MPB) composition ($0.46{\leq}x{\leq}0.50$). The dielectric constant showed a maximum value at x = 0.46 and the maximum values in (1-x)PYN-xPT decreased with higher PT contents. The phase transition temperatures of (1-x)PYN-xPT solid solutions increased over the whole composition ranges tested ($0.40{\leq}x{\leq}0.60$).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.84-84
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• 2009

$BaTiO_3$는 perovskite 구조를 가지는 대표적인 강유전체 재료로서 MLCC (Multi Layer Ceramic Capacitor), PTC thermistor등에 널리 사용되어지고 있다. 최근 고용량 MLCC의 상업화와 함께 나노크기를 갖는 tetragonal phase의 $BaTiO_3$ 입자를 합성하기 위한 다양한 제조방법이 제시되고 있다. 또한 유전특성과 온도특성 및 신뢰성을 향상시키기 위해 많은 첨가제들이 연구되어지고 있다. 따라서 본 연구에서는 희토류 원소인 $Y_2O_3$를 첨가하여 유전특성 및 온도특성을 향상시키고자 하였다. 본 실험에서는 150nm 크기를 갖는 pure $BaTiO_3$ 분말을 사용하고 $Y_2O_3$의 양은 0.02 ~ 0.1wt%로 변수를 주어 첨가하였으며, 최적의 소결 조건을 찾기 위하여 1200, 1230, $1250^{\circ}C$에서 소결을 진행하였다. 실험방법으로는 균일한 혼합을 위하여 Iso-alcohol을 이용하여 48시간 ball-mill 하였으며 오븐에서 건조 후 ${\Phi}15$로 성형하여 소결을 진행하였다. 실험결과로는 $Y_2O_3$ 첨가량이 0.02wt% 부터 상온부터 상전이 온도 부근의 유전율 기울기는 완만해 지는 것을 확인할 수 있었으며, 소결시편의 정방정비 (tetragonality)도 뚜렷하게 나타났다. $Y_2O_3$ 첨가랑이 0.1 wt% 일 때는 첨가량의 증가로 인해 강유전성이 상쇄됨을 나타냈다. 이는 $2450^{\circ}C$에 이르는 매우 높은 용융온도와 $2350^{\circ}C$까지 상전이가 는 $Y_2O_3$를 미량 첨가할 때, 고온에서 높은 화학적 안정성과 내열성을 가져 온도 안정성이 향상된 것으로 판단된다.

• Korean Journal of Crystallography
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• v.3 no.2
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• pp.120-128
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• 1992

Single crysals of BaTiO3 were grown by TSSG technique at various cooling rates. Morpolo girts, defects and domain structures of the grown crystals were investigated. At the cooling rates below 0.5℃/hr, equant single crystals were obtained and the 11111 faces were dominantly developed. If the cooling rate was much faster or if the vortical temperature gradient in the so lotion was very large, the solution became unstable and the needle formed BasTil04 o crystals were precipitated. Two sets of parallel lamella domains are arranged perpendicular to each other and the irregularly shaped boundaries are fixed between them. These sets of domains show remarkable orientation contrast in x-ray topography. Heating the crystal above 127℃, the phase transition from tetragonal to cubic occurs. The phase transition front (PTF) moves in the direction of temperature gradient. Domains in the tetragonal phase are successively rearranged and regular strain patterns appear in the cubic phase. The habit plane of PTF in BaTi03 is found to deviate from a l1101 lattice plane by app roximately 9°.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.817-821
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• 1998

$BaTiO_3$ particles were prepared using $Ba(OH)_2{\cdot}8H_2O$ and $Ti(OC_2H_5)O_4$ by the hydrothermal method and their characteristics treated at the various temperatures have been investigated. This prepared $BaTiO_3$ powder includes a very small amount of $H_2O$ and $OH^-$. By increasing the treated temperature from $200^{\circ}C$ to $1000^{\circ}C$, the mean particle size was accordingly increased from $0.022{\mu}m$ to $0.072{\mu}m$ and the tetrogonality(c/a)was increased from 1.02 to 1.2 so that the phase transition to tetroganal takes place. $BaTiO_3$ sintered at $1250^{\circ}C$ after heat treatment at $400^{\circ}C$ for 3 hrs showed a specific dielectric constant of 8120 and surface activation energy was 9680 kcal/mol.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.5
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• pp.395-403
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• 2006

This paper has proposed a new dead time compensation method for a voltage-fed PMW inverter. In the voltage-fed PMW inverter, a voltage distortion is generated by the dead time effect and the nonlinear characteristics of the switching devices. Especially, the distorted voltage causes 5th and 7th harmonics in the stationary phase currents, and 6th harmonic in the synchronous phase currents. As a result, the integrator output of the synchronous PI current regulator has the ripple corresponding to six times of the inverter output frequency. In this paper, the signal of the integrator output of the d-axis current regulator is used as the control signal for the dead time compensation. The experimental and simulation results are presented to verify the validity of the proposed method.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.677-683
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• 2004

Nd:LLM (Nd:LiLa(MoO$_4$)$_2$) single crystals for the laser host material were grown by the Czochralski method. The Nd:LLM grown single crystals cracked easily, and the reasons of cracks are generally related with phase transition, incongruent melting, chemical heterogeneity of composition, geometric thermal structures of imbalance and growth direction. We confirmed that phase transition is not observed by TG-DTA thermal analysis, and the XRD analysis revealed congruent melting in our products. It was confirmed that the volatilization of Li$_2$O composition is the important reason of chemical heterogeneity. The geometric thermal profile of the resistance furnace of our own design was controlled with a crucible height. Also, Nd:LLM crystal affected growth direction, and was the best quality in case of (101) growth direction. The distribution and effective distribution coefficient of Nd$^{3+}$ ion were accomplished by PIXE analysis.s.