• Journal of Power Electronics
• /
• 제16권4호
• /
• pp.1598-1611
• /
• 2016

In some special occasions with strict size requirements, such as mine hoists, improving the design accuracy of the forced-air cooling systems of NPC three-level inverters is a key technology for improving the power density and decreasing the volume. First, a fast power-loss calculation method was brought. Its calculation principle introduced in detail, and the computation formulas were deduced. Secondly, the average and dynamic power losses of a 1MW mine hoist acting as the research target were analyzed, and a forced-air cooling system model based on a series of theoretical analyses was designed with the average power loss as a heat source. The simulation analyses proves the accuracy and effectiveness of this cooling system during the unit lifting period. Finally, according to an analysis of the periodic working condition, the maximum power-loss range of a NPC three-level inverter under multi cycle operation was obtained and its dynamic power loss was taken into the optimized cooling system model as a heat source to solve the power device damage caused by instantaneous heat accumulation. The effectiveness and feasibility of the optimization design based on the dynamic power loss calculation of the maximum power-loss range was proved by simulation and experimental results.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2001년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
• /
• pp.44-46
• /
• 2001

This paper describes the use of the PHOENICS CFD package for the simulation of the high-current period of the arcing process in a hybrid rotating arc/auto expansion by interrupter. The operating principle of this device depends on rapid arc rotation due to the magnetic field created by the fault current through a coil which is mounted on contacts and also relies on the principle of thermal expansion created by arc energy in extinguishing chamber and finally causes pressure rise in expansion volume. This paper is divided into three main sections. The first gives a brief overview of the interrupter. The second section gives a full description of the methods used in the calculation. The final section presents some sample results for the hybrid interrupter.

• Bulletin of the Korean Chemical Society
• /
• 제12권2호
• /
• pp.228-238
• /
• 1991

Generalized multichannel quantum defect theory [C. H. Greene et al. Phys. Rev., A26, 2441 (1982)] is implemented to the vibrational predissociation of triatomic van der Waals molecules. As this is the first one of such an application, the dependences of the quantum defect parameters on energy and radius are examined carefully. Calculation shows that, in the physically important region, quantum defect parameters remain smoothly varying functions of energy for this system as in atomic applications, thus allowing us very coarse energy mesh calculations for the photodissociation spectra. The choice of adiabatic or diabatic potentials as reference potentials for the calculation of quantum defect parameters as done by Mies and Julienne [J. Chem. Phys., 80, 2526 (1984)] can not be used for this system. Physically motivated reference potentials that may be generally applicable to all kinds of systems are utilized instead. In principle, implementation can be done to any other predissociation processes with the same method.

• 전기화학회지
• /
• 제14권1호
• /
• pp.33-37
• /
• 2011

$Li_4Ti_5O_{12}$는 우수한 안정성으로 고출력 배터리의 음극 물질로 주 목 받고 있다. 그러나 절연체로서 전도도의 개선이 필요한 상황으로 다양한 방법이 시도되고 있다. 본 연구에서는 Cr 도핑을 통해서 $Li_4Ti_5O_{12}$의 전도도 향상을 목표로 하였으며, X-선 흡수 실험 및 FEFF 8.4 코드를 이용한 제일원리 계산을 통해서 도핑에 의한 미세 구조 및 전자 구조의 변화를 분석하였다. Cr 도핑은 페르미 레벨을 Cr d 밴드의 중심에 위치시켜 전도성을향상시켰으며, Ti d 밴드의 전자밀도를 높여 XANES pre-edge및 White line의 변화를 야기했다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
• /
• pp.148-151
• /
• 2003

The spin density of ${\beta}-MnO_2$ structure was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}O_{56}]^{-52}$. The ${\beta}-MnO_2$ is a paramagnetic oxide semiconductor material having the energy band gap of 0.18 eV and an 3 loan-pair electrons in the 3d orbital of an cation. This material exhibits spin-only magnetism and has the magnetic ordering temperature of 94 K. Below this temperature its magnetism appears as antiferromagnetism. The calculations of electronic state showed that if the initial spin condition of input parameters changed, the magnetic state changed from paramagnetic to antiferromagnetic. When d orbital of all Mn atoms in cluster had same initial spin state as only up spin, paramagnetic spin density distribution appeared by the calculation. On the other way, d orbital had alternately changed spin state along special direction the resulted spin distribution showed antiferromagnetism.

• 한국자기학회지
• /
• 제15권6호
• /
• pp.299-302
• /
• 2005

전이금속 Fe-Pt 나노선의 자기적 성질을 수도퍼텐셜 및 전전자(all-electron) 제일원리 전자구조 계산 방법으로 연구하였다. 직선 구조와 지그재그 구조에 대해서 결합에너지를 계산함으로써 안정된 구조를 결정했고, 결합거리, 결합각도, 자기모멘트, 스핀밀도, 상태밀도 등을 계산함으로써 전이금속 나노선의 구조적 성질과 자기적 성질을 연구하였다. Fe-Pt 나노선의 경우에 지그재그 구조가 직선 구조보다 더 안정된 것으로 계산되었고, 직선 구조에 비해서 결합길이는 증가하지만 자기모멘트는 감소하였다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
• /
• pp.99-102
• /
• 2003

The electronic structure of ${\beta}-MnO_2$ having impurities in the site of Mn was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}MO_{56}]^{-52}$ (M = transient metals). Madelung potential and spin polarization were considered for more exact calculations. As results of calculations, the energy levels of all electron included in the model were obtained. The energy band gap and positions of impurity levies were discussed in association with impurity 34 orbital that seriously affect electrical properties of $MnO_2$. It was shown that the energy band gap decreased with the increase of the atomic number of transient metal impurity.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
• /
• pp.259-262
• /
• 2003

The surface electronic state of rutile $TiO_2$, which is an oxide semiconductor and has a wide band gap of 3.1 $\sim$ 3.5 eV, was calculated by DV-$X_{\alpha}$ method, which is a sort of the first principle molecular orbital method and uses Hartre-Fock-Slater approximation. The $[Ti_{15}O_{56}]^{-52}$ cluster model was used for the calculation of bulk state and the $[OTi_{11}O_{34}]^{-24}$ model for the surface state calculation. After calculations, the energy level diagrams and the deformation electron density distribution map were compared in both models. As results, it was identified that the surface energy levels are found between the valence and conduction band of bulk $TiO_2$ on the surface area. The energy values of these surface-induced levels are lower than conduction band of bulk $TiO_2$ by 0.1 $\sim$ 1 eV. From this fact, it is expected that the surface energy levels act as donar levels in n-type semiconductor.

• 한국자기학회지
• /
• 제17권4호
• /
• pp.152-155
• /
• 2007

다중강전자 상태의 $YMnO_3,\;ScMnO_3$의 전자구조와 자기구조를 국소스핀밀도근사(LSDA)를 이용하여 계산하였다. 강자성 상태이며 강유전 상태의 전자구조는 육방정계 구조로 인하여 Mn 3d 에너지띠가 분리되어 띠틈을 나타내었다. 이러한 에너지 띠틈과 작은 Y, Sc 이온의 반경으로 인하여 $YMnO_3,\;ScMnO_3$는 반강자성 강유전적 성질을 가지는 다중강전자 구조를 가지고 있음을 보았다. 또한 총에너지 계산을 통하여 반강자성, 강유전 상태가 가장 안정됨이 실험과 일치하였다.

• 동의생리병리학회지
• /
• 제33권3호
• /
• pp.163-168
• /
• 2019

In order to enhance the 8 principle pattern diagnosis rate comparing with diagnostic method by self-report questionnaire on cold/heat pattern in the clinical practice, a new diagnostic method using form-color-pulse-symptom (FCPS) system is proposed. FCPS system is composed of outputs of cold/heat pattern through the calculation process of contribution degree to the cold, heat pattern and qi, blood, yin, yang deficiency patterns, based on analysis of 16 mechanisms of disease calculated by diagnostic system of oriental medicine (DSOM) first. And second component is an output of differentiated 8 principle patterns in detail through binding and calculating process with digital informations of pulse, color, form, constitution obtained by computerized measurement system. Putting together above two processes consecutively, cold-heat complex or true/false cold/heat patterns and personalized characters of cold/heat patterns of each patient can be subdivided through a computation method of determining each pattern. In conclusion, 8 principle pattern identification can be performed more accurately using FCPS system than existent self report questionnaire method. These hypothetic proposal is needed to be proven by clinical trial for the future and then the accurate numbers used in each calculational function should be revised properly.