• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.734-739
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• 2003

최근 상업용 빌딩, 주거용 빌딩 및 공장등의 저전압 3상 4선식 배전계통에서 PC, UPS, 정류기기, 조명장치 및 사무용기기등 비선형 부하의 사용이 증가하고 있으며, 이로 인한 과도한 중성선 전류는 중성선의 고장, 변압기의 과열 및 중성선과 접지사이의 전압강하등 심각한 문제를 야기시키고 있다. 본 논문에서는 3상 4선식 배전계통에서 중성선 전류 저감을 위한 새로운 능동전력필터를 제안한다. 제안한 방식은 제어가 간단하고 부하용량대비 인버터등 장치의 용량이 작아 저가격으로 실현할 수 있다. 제안한 시스템은 이론적인 분석과 모의실험 및 실험에 의하여 그 타당성을 입증한다.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.607-611
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• 2002

최근 상업용 빌딩, 주거용 빌딩 및 공장등의 저전압 3상 4선식 배전계통에서 PC, UPS, 정류기기, 조명장치 및 사무용기기등 비선형 부하의 사용이 증가하고 있으며, 이로 인한 과도한 중성선 전류는 중성선의 고장, 변압기의 과열 및 중성선과 접지사이의 전압강하등 심각한 문제를 야기 시키고 있다. 본 논문에서는 3상 4선식 배전계통에서 중성선 전류 저감을 위한 새로운 능동전력필터를 제안한다. 제안한 방식은 제어가 간단하고 부하용량대비 인버터등 장치의 용량이 작아 저 가격으로 실현할 수 있다. 제안한 시스템은 이론적인 분석과 모의실험 및 실험에 의하여 그 타당성을 입증한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.272.1-272.1
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• 2016

In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers. From the UV photoemission/inverse photoemission spectroscopy (UPS/IPES) results and ab initio calculations, significant changes of the Fermi level and band gap were observed. The deformed band structure also exhibits a Van Hove singularity at specific energies in the UV absorption experiment and ab initio calculations. Our results, including the synthesis of a strained ultrathin topological insulator, suggest a new direction for electronic and spintronic applications for the future.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.372-378
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• 2012

This paper deals with a 3-phase voltage disturbance generator for a performance test of custom power devices such as dynamic voltage restorers (DVR), dynamic uninterruptable power supplies (UPS), etc. The operating principle of the proposed circuit is described in each mode of voltage sag, swell, outage, and unbalance. The main components of the proposed disturbance generator are silicone controlled rectifier (SCR) thyristors, variable autotransformers, and transformers. Therefore, the disturbance generator can be implemented with a considerably low cost compared to the conventional pulse width modified (PWM) inverter and converter type generators. Furthermore, it has good features of high reliability with simple structure, high efficiency caused by no PWM switching of the SCR thyristors, and easy control with a wide variation range. To verify the validity of the proposed scheme, simulations and experiments are carried out.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1528-1538
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• 2018

In this paper, configuration of $1-{\phi}$ seven-level boost DC-link cascade based reversing voltage multilevel inverter (BDCLCRV MLI) is proposed for uninterrupted power supply (UPS) applications. It consists of three level boost converter, level generation unit and full bridge circuit for polarity generation. When compared with conventional boost cascaded H-bridge MLI configurations, the proposed system results in reduction of DC sources, reduced power switches and gate drive requirements. Inverter switching is accomplished by providing appropriate switching angles that is generated by any optimization switching angle techniques. Here, round modulation control (RMC) method is taken as the optimization method and switching angles are derived and the same is compared with various switching angles methods i.e., equal-phase (EP) method, and half-equal-phase (HEP) method which results in improved quality of obtained AC power with lowest total harmonic distortion (THD). Reduction in DC sources and switch count makes the system more cost effective. A simulation and prototype model of $1-{\phi}$ seven-level BDCLCRV MLI system is developed and its performance is analyzed for various operating conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.1
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• pp.1-7
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• 2016

A Urea-SCR(Selective Catalytic Reactor) system, which converts nitrogen oxides into nitrogen and water in the presence of a reducing agent, creates a major exhaust gas aftertreatment system for NOx reduction among other compounds. With regard to vehicle applications, a urea solution was chosen based on its eutectic composition of a 32.5wt% urea-water solution. An important advantage of this eutectic composition is that its melting point of $-11.7^{\circ}C$ is sufficiently low to avoid solidification in cold environments. However, the storage tanks must be heated separately in case of low ambient temperature levels to ensure a sufficient amount of liquid is available during scheduled start ups. In this study, therefore, a numerical investigation of three-dimensional unsteady heating problems analyzed to understand the melting processes and heat transfer characteristics including liquid volume fraction, temperature distributions, and temperature profiles. The investigations were performed using Fluent 6.3 commercial software that modeled coolant and electric heater models based on a urea solution. It is shown that the melting performance with the electric heater is higher than a coolant heater and is more efficient.