• Journal of Power Electronics
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• v.9 no.2
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• pp.215-223
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• 2009

A design methodology for transformers including integrated and center-tapped structures for LLC resonant converters is proposed. In the LLC resonant converter, the resonant inductor in the primary side can be merged in the transformer as a leakage inductance. And, the absence of the secondary filter inductor creates low voltage stress on the secondary rectifiers and is cost-effective. A center-tapped structure of the transformer secondary side is widely used in commercial applications because of its higher efficiency and lower cost than full-bridge structures in the rectifying stages. However, this transformer structure has problems of resonance imbalance and transformer inefficiency caused by leakage inductance imbalance in the secondary side and the position of the air-gap in the transformer, respectively. In this paper, gain curves and soft-switching conditions are derived by first harmonic approximation (FHA) and operating circuit simulation. In addition, the effects of the transformer including integrated and center-tapped structures are analyzed by new FHA models and simulations to obtain an optimal design. Finally, the effects of the air-gap position are analyzed by an electromagnetic field simulator. The proposed analysis and design are verified by experimental results with a 385W LLC resonant converter.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.81.2-81.2
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• 2011

The gas diffusion layer (GDL) consists of two main parts, the GDL backing layer, called as a substrate and the micro porous layer (MPL) coated on the GDBL. In this process, carbon particles of MPL penetrates to the GDBL consequently forms MPL penetration part. In this study, the micro porous layer (MPL) penetration thickness is determined as a design parameter of the GDL which affect pore size distribution profile through the GDL inducing different mass transfer characteristics. The pore size distribution and water permeability characteristics of the GDL are investigated and the cell performance is evaluated under fully/low humidification conditions. Transient response and voltage instability are also studied. In addition, to determine the effects of MPL penetration on the degradation, the carbon corrosion stress test is conducted. The GDL that have deep MPL penetration thickness shows better performance in high current density region because of enhanced water management, however, loss of penetrated MPL parts is shown after aging and it induces worse water management characteristics.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.885-886
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• 2006

We have proposed a 100 MVA, 3 phases, 154 kV class HTS transformer which will substitute for 60 MVA conventional transformer. In this paper, we designed conceptually the structure of the superconducting windings of a single phase 33 MVA transformer. The power transformer of 154 kV class has a tertiary winding besides primary and secondary windings. So the HTS transformer should have the 3rd superconducting winding, it makes the cost of the HTS transformer high and the efficiency low. Further more we considered On Load Tap Changer (OLTC) in HTS power transformer. OLTC equipment is required for fitting to a power transformer by which the voltage ratio between the windings can be varied while the transformer is on load. We analyzed the electrical characteristics of the HTS transformer such as magnetic stress and AC loss.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.2
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• pp.82-88
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• 2009

Power capacitor is generally installed to compensate for the low power factor of inductive load But it has been used as passive filter to reduce harmonics generated by the power conversion device. Passive filter is composed by the series connection of reactor and capacitor. Because passive filter has play an important role on the absorber of harmonics, it takes voltage and current stress, follows partially burned on flamed and degradation, finally it has not guaranteed normal life. In this paper, we analyzed the effect that passive filter installed at the source side of PWM inverter is received by harmonics absorption.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.12
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• pp.776-780
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• 2016

Recently, energy harvesting technology is increasing due to the fossil fuel shortages. To compensate problem of low generating power than other energy harvesters, many researchers have studied about piezoelectric harvester for obtaining high output. In this paper, four kinds of unimorph based piezoelectric harvesters were proposed and its generating characteristics were studied. Each of the piezoelectric harvesters has three, four, and six unimorph arms, respectively, and the arms are symmetrically arranged from one central point. The centrosymmetric structure of the harvesters guarantees more stable and multiplied generation than a cantilever-type harvester since the arms of the harvester resonate at same frequency. Resonance frequency, output voltage, displacement, and stress characteristics of the generator were analyzed by using a FEM (finite element method) program. Harvesters were fabricated on the basis of analysis results. Experimental results were compared with simulated results.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.376-379
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• 2005

High efficiency and low cost sustain driver for plasma display panel (PDP) with current fed is proposed. Main concept of the proposed circuit is using the current source to charge and discharge panel. As a result, all power switches can achieve the zero voltage switching (ZVS) and every auxiliary switch can also do the zero current switching (ZCS). Moreover, since the inductor current can compensate the discharge current, the current stress of all power switches can be reduced considerably. Furthermore, it has features as a simpler structure, less mass, less cost, and lower electromagnetic interference than prior circuit.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.1
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• pp.42-48
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• 2016

Light-emitting diode (LED) drivers are recently replacing fluorescent lamps; these drivers can operate adaptively with various ballasts without modifying and removing such ballasts. To satisfy these trends, a LED driver that is compatible with both electronic and magnetic ballasts is proposed in this study. Unlike conventional LED drivers, the proposed driver has a ballast recognition circuit and a mode selection circuit to operate ballasts at optimal conditions. Therefore, it features low voltage stress, high efficiency, and good compatibility with both electronic and magnetic ballasts. Moreover, it can be compatible with a wide selection of ballasts from various manufacturers. To confirm the validity of the proposed LED driver, results of the theoretical analysis and experimental verification performed on a 15 W-rated prototype are presented.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.6
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• pp.1-6
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• 2008

In this paper describes the process of designing a protection circuit against an open or short electronic ballast. An open electronic ballast creates high voltages in a regular period, which a lies voltage stress on switching devices. On the other hand, a shorted output generates excessive current, causing problems such as heat generation in the ballast and reduced lifespan of semiconductor devices. This study proposes a protection circuit consisting of TTL and passive devices to resolve the problems. The proposed protection circuit offers the benefits of low cost and high reliability. The proposed circuit was connected to an actual ballast to demonstrate its applicability.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.327-327
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• 2007

This paper reports the simulation results of piezoelectric microspeakers due to structural changes(diaphragm materials, corrugation width and electrode shapes). When we compared the dependence of diaphragm material properties, the microspeaker with LTO(Low Temperature Oxide) diaphragm shows higher deflection than that of silicon nitride diaphragm, even though the resonant frequencies are almost same in both cases. In case of circular-electrode microspeaker, the deflection of diaphragm is about $16\;{\mu}m$ at 20 V, and it decreases as the corrugation width is decreased. However, the deflection of diaphragm with the square-electrode reveals almost twice times higher value at the same applied voltage than the circular one, and it increases as the corrugation depths are decreased from $30\;{\mu}m\;to\;10\;{\mu}m$. The first resonant frequency of microspeakers present about 1.8 kHz in circular-electrode and 1.2 kHz in square-electrode, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.178-179
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• 2005

ESD(Electrostatic Discharge) 보호에 응용되는 소자는 ESD가 발생했을 때, 빠르게 턴-온되어 외부로부터 EOS(Electric OverStress)를 차단함으로서 집적회로 내부의 코어를 보호해 주어야 한다. 이러한 기능에 충실한 LVTSCR(Low-Voltage Silicon Controlled Rectifier)은 트리거링 전압을 기존의 SCR보다 낮추어 ESD에 대해 민감한 반응을 할 수 있도록 개선한 소자이다. 그러나 트리거링 전압을 낮추면서 래치업 전압 또한 낮아지는 특성이 trade-off 관계로 맞물려 있어, LVTSCR의 단점인 낮은 래치업 전압을 효과적으로 다루는 것이 큰 이슈가 되고 있다. 본 논문에서는 LVTSCR의 ESD 보호에 대한 응용시 발생 가능한 래치업을 차폐하는 회로적 방법을 제시하였다. 제시된 새로운 구조의 차폐회로는 LVTSCR에서 래치업이 발생했을 때, 천이 전류를 감지하여 래치업이 발생되는 소자에 대한 전원을 스스로 차폐시켜 래치업에 대한 안정성을 시뮬레이션으로 검증하였다.