• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.5
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• pp.406-414
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• 2009

To cope with the high power density and low cost in switching power supply, LLC resonant converters with the two resonant tank circuits composed of resonance capacitors and two transformers are proposed in this paper. Each transformers used for the proposed resonant circuits are parallel connected in the primary and series connected in the secondary to reduce the current unbalance. The proposed LLC resonant converters are described and verified on 300W experimental prototype.

• Proceedings of the KIPE Conference
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• 2017.07a
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• pp.286-287
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• 2017

본 논문은 철도 차량 구동용 IPMSM 제어를 위한 속도 영역별 PWM 알고리즘을 제안한다. 철도 차량의 고속영역 제어는 인버터 전압 이용률을 최대화 할 수 있는 1-Pulse 제어 기법이 요구된다. 그러나, SPWM을 이용한 비동기 1-Pulse 제어는 출력 전류의 불균형을 초래한다. 따라서, 고속영역 제어를 위해 동기화 시킨 후 SPWM을 이용한 1-pluse 제어는 필수적이다. 본 논문에서는 비동기 모드로 제어를 시작하여 과변조 영역 이전에 지령 전압과 삼각파 주파수를 동기화 시킨 후 고속 영역운전을 하는 PWM 알고리즘을 제안한다. 본 논문에서 제안하는 알고리즘은 시뮬레이션으로 검증한다.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2166-2168
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• 2005

This paper presents the frequency - dependent characteristics of leakage currents flowing through ZnO varistor. The leakage current - voltage (V-I) characteristic curves of the commercial ZnO varistor were measured. The resistive leakage current was increased with increasing the magnitude and frequency of the applied voltage in the low conduction region. The power losses of ZnO varistor increase as the frequency of applied voltage increases, because of the dielectric loss related to the frequency of the test voltage.

• Proceedings of the KIPE Conference
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• 2008.10a
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• pp.143-145
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• 2008

최근 각종 전자기기의 슬림화 추세에 따라 PDP PSU(Power Supply Unit) 또한 슬림화가 진행되고 있다. 슬림화를 위해서는 방열판과 벌크(Bulk) 커패시터, 입력단의 필터와 인덕터류, 그리고 변압기의 높이를 줄이는 것이 중요하다. 그 중에서도 변압기의 높이를 줄이는 것이 가장 큰 관건이다. 하나의 변압기를 사용할 경우 슬림화의 한계성을 가지기 때문에 적용된 변압기는 두 개의 LLT 변압기로 구성 하였으며 1차측과 2차측의 결선 방법을 통해 두 LLT변압기간의 전류 불균형 문제를 최소화 할 수 있도록 하였다. 그리고 높이 35mm 시제품을 제작하여 50HD PDP 전원에 적용시켜 검증한 결과를 나타내었다.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.343-344
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• 2015

본 논문은 고속영역에서 3차 고조파의 영향을 고려한 5상 유도전동기의 약계자 운전을 제안한다. 5상 유도전동기는 집중권의 형태로 되어있어 공극 자속이 제 3차 공간 고조파 성분을 포함한다. 따라서 5상 유도전동기의 역기전력은 3차 고조파가 포함된 형태이므로, 5상 유도전동기의 약계자 운전은 3차 고조파 성분을 고려하여 수행해야 한다. 약계자 운전에 앞서 정격 이하의 속도에서는 간접벡터제어를 사용하고, 정격이상의 고속 영역에서는 최대 토크 발생과 전압 및 전류 제한 영역을 고려한 약계자 운전을 수행한다. 본 논문에서는 3차 고조파를 고려한 5상 유도전동기의 약계자 운전을 시뮬레이션으로 검증한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.490-493
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• 2004

A 3-DOF actuator which has new principle and very simple structure is proposed. Its principle seems to be similar to conventional electromagnetic actuators, that is, to utilize the relation of control and bias fluxes produced by coils and permanent magnets, respectively, but the coils and permanent magnets of the proposed actuator are fixed in the stator. Such a structure helps to optimally design the actuator for its use. Some experimental and FEM analysis results show the feasibility of the proposed actuator and some characteristics of system that are useful lot structure design and control.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.4
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• pp.71-76
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• 2015

Recently, light emitting diodes (LEDs) have been studied to improve their efficiencies for the uses in various fields. Particularly in the aspect of chip structure, via hole type vertical LED chip is developed for improvement of light output power, and heat dissipations. However, current vertical type LEDs have still drawback, which is current concentration around the n-contact holes. In this research, to solve this phenomenon, we introduced isolation layer under n-contact electrodes. With this sub-electrode, even though the active area was decreased by about 2.7% compared with conventional via-hole type vertical LED, we could decrease the forward voltage by 0.2 V and wall-plug efficiency was improved approximately 4.2%. This is owing to uniform current flow through the area of n-contact.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.7
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• pp.1491-1496
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• 2005

We fabricated the $Pb_{0.72}La_{0.28}TiO_3$ (PLT(28)) thin film successfully by using the sol-gel method and characterized it to evaluate its potential for being utilized as the capacitor dielectrics of ULSI DRAMs. In our sol-gel process, the acetates were used as the starting materials. Through the TGA-DTA analysis, we established the excellent fabrication conditions of the sol-gel method for the PLT(28) thin film. We obtained the dense and crack-free PLT(28) thin film of $100\%$ perovskite phase by drying at $350^{\circ}C$ after each coating and final annealing at $650^{\circ}C$. Electrical properties of PLT(28) thin film were measured through formation on the $Pt/Ti/SiO_2/Si$ substrate and its dielectric constant and leakage current density were measured as 936 and $1.1{\mu}A/cm^2$, respectively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.784-787
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• 2002

We prepared the PLT(28) thin film by using sol-gel method and investigated the structure and electrical properties of the film. With the XRD and AFM analyses, it is found that PLT(28) thin film annealed at 6sot has a complete perovskite structure and its surface roughness is about 22$\AA$. We prepared PLT(28) thin film on the Pt/TiO$_{x}$SiO$_2$/Si substrate, in which the specimen has a planar capacitor structure, and analyzed the electrical properties of PLT(28) thin film. In result, PLT(28) thin film has a paraelectric phase and its dielectric constant and loss tangent at 10kHz are 761 and 0.024, respectively. Also, the storage charge density and leakage current density of PLT(28) thin film at W are 134fC/$\mu$m2 and 1.01 $\mu$A/cm2, respectively. As a result of this, we concluded that the PLT(28) thin film is a promising material to be used as a capacitor dielectrics for next generation DRAM.M.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.4
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• pp.65-75
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• 1998

The $CO_2$ welding with 100% $CO_2$ gas is commonly used because of its cost and efficiency. Arc phenomena and spattering ratio of the $CO_2$ welding are influenced by various factors such as chemical compositions of welding wire, shielding gas, welding condition and welding power source etc.. Spattering ratio is predominantly influenced by the welding condition which determines a droplet transfer rode. In this study, arc phenomena and spattering ratio are investigated by using two type of FCW(titania type, semi-metal type). Then, the welding quality and optimum welding condition can be selected. From this study, the following results ware obtained; 1) In low current range(140A), FCW up to welding voltage(22V) resulted in a typical short circuit transfer, increase of spattering ratio and growth of spatter diameter. 2) In high current range(320A), the arc stability in titania FCW of a typical globular transfer is better than that of semi-metal FCW.