• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1552-1553
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• 2011

The HVDC transformer which is one of the main equipments for HVDC(High Voltage Direct Current) electric power transmission systems is exposed to not only AC voltage but also the inflowing DC voltage which comes from the DC-AC converter systems. Therefore, the HVDC transformer insulation system is required to withstand the electric field stress under AC, DC and DC polarity reversal conditions. However the electric field distributions under those conditions are different because the AC electric field and DC electric field are governed by permittivity and conductivity, respectively. In this study, the changes of electric potential and electric field of conventional AC transformer insulation system under DC polarity reversal test condition were analyzed by FEM(Finite Element Method). The DC electric field stress was concentrated in the solid insulators while the AC electric field stress was concentrated in the mineral oil. In addition, the electric stress under that condition which is affected by the surface charge accumulation at the interfaces between insulators was evaluated. The stress in some parts could be higher than that of AC and DC condition, during polarity reversal test. The result of this study would be helpful for the HVDC transformer insulation system design.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.133-141
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• 2020

The use of high-gain-voltage step-up converters for distributed power generation systems is being popularized because of the need for new energy generation and power conversion technologies. In this study, a new constructed high-gain-boost DC-DC converter was proposed to coordinate low voltage output DC sources, such as PV or fuel cell systems, with high DC bus (380 V) lines. Compared with traditional boost DC-DC converters, the proposed converter can create higher gain and has wider input voltage range and lower voltage stress for power semiconductors and passive elements. Moreover, the proposed topology produces multilevel DC voltage output, which is the main advantage of the proposed topology. Steady-state analysis in continuous conduction mode of the proposed converter is discussed in detail. The practicability of the proposed DC-DC converter is presented by experimental results with a 300 W prototype converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.91-102
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• 2013

This paper proposes the improved LCCT(Inductor-Capacitor-Capacitor-Trans) Z-source DC-DC converter (Improved LCCT ZSDC) which can generate the bipolar output voltages according to duty ratio D. The proposed converter has the characteristic and structure of Quasi Z-source DC-DC converter(Quasi ZSDC) and conventional LCCT Z-source DC-DC converter(LCCT ZSDC). To confirm the validity of the proposed method, PSIM simulation and a DSP based experiment were performed for each converter. In case which the input DC voltage is 70V, the bipolar output DC voltage of positive 90V and negative 50V could generate. Also, as comparison result of the capacitor voltage ripple in Z-network and the input current under the same condition for each converter, the voltage stress and the capacitor voltage in Z-network of the proposed method were lower compared with the conventional methods. Finally, the efficiency for each method was investigated according to load variation and duty ratio D.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.3
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• pp.244-252
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• 2002

The electrical and dielectric behavior fort DC accelerated aging stress of P $r_{6}$ $O_{11}$-based Zno varistors cnsisting of ZnO-P $r_{6}$ $O_{11}$-CoO-C $r_2$ $O_3$-E $r_2$ $O_3$ were investigated with sintering temperature in the range of 1325~1345$^{\circ}C$. The varistor ceramics with increasing sintering temperature were more densified. A more densified varistors leaded to high stability for DC accelerated aging stress. Furthermore, the stability for DC accelerated aging stress was increased with the leakage current and dtan $\delta$/dV decreasing in order of 1325longrightarrow1335longrightarrow1345longrightarrow134$0^{\circ}C$ in sintering temperature. It was found that the stability for DC stress is affected more greatly by the leakage current and dtan $\delta$/dV than the densification. It is considered that the stability of varistors for DC stress can be estimated by considering the factors, such as the densification, leakage current, and dtan $\delta$/dV. As a result, the varistor sintered at 134$0^{\circ}C$ exhibited the highest stability, with %$\Delta$ $V_{lmA}$=-1.54%, %$\Delta$$\alpha$=-2.49%, %$\Delta$ $I_{\ell}$=+240.68%, 5%$\Delta$tan$\delta$=+29.96%.96%.96%.%.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1019-1021
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• 1992

This paper deals with the stress of the converters using the resonant switches. It is represented the reduction of the voltage and current stresses. According to the configuration of the multiple poly-phase converter. Especially, about buck ZVS-QRC it is studied the reduction of the voltage stress, and represented the result of simulation.

• 전자공학회논문지 IE
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• v.45 no.4
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• pp.7-10
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• 2008

In this work investigates hot carrier stress on the RF power of SOI MOSFET using load-pull measurement. We found that the RF power characteristics are affected by the hot carrier stress, and the DC performance of SOI MOSFET is clearly degraded after hot carrier stress at constant voltage measurement. And these experimental observations can be explained by the change of DC performance degradation coefficient under hot carrier stress.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.498-501
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• 2004

In this study, the threshold voltage and the response time of thermal stressed TN-LCDs showed the same performances on no thermal stressed TN-LCDs. There was little change of value in TN cells. Also, the transmittances of TN-LCDs on the rubbed PI surface were almost same while increasing thermal stress time. However, the thermal stability of TN cell was decreased by the high thermal stress for the long duration. Residual DC was decreased as the thermal stress increases. Especially, when TN cell was stressed more and more by heating, residual DC was changed a lot. As a result, the residual DC property of LCD in projection TV is affected very much by heating.

• Journal of Power Electronics
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• v.9 no.3
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• pp.335-342
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• 2009

The Z-source inverter (ZSI) provides unique features such as the ability to boost dc voltage with a single stage simple structure. Although the dc capacitor voltage can be boosted by a shoot-through state, the voltage stress across the switching devices is rapidly increased, so high switching device power is required at the ZSI. In this paper, algorithms for minimizing the voltage stress are suggested. The possible operating region for obtaining a desired ac output voltage according to both the shoot-through time and active state time is investigated. The reference capacitor voltages are derived for minimizing the voltage stress at any desired ac output voltage by considering the dc input voltage. The proposed methods are carried out through the simulation studies and experiments with 32-bit DSP.

• Journal of Power Electronics
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• v.18 no.2
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• pp.356-363
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• 2018

The combination of a buck converter and a forward converter can be considered to accomplish a high step-down non-isolated converter. To decrease the insufficient step-down ratio of a regular buck converter and to distribute switch voltage stress, a forward-integrated buck (FIB) converter is proposed in this paper. The proposed interleaved DC-DC converter provides an additional step-down gain with the help of a forward converter. In addition to its simple structure, the transformer flux reset problem is solved and an additional magnetic core reset winding is not required. The operational principle and an analysis of the proposed FIB converter are presented and verified by experimental results obtained with a 240 W, 150 V/24 V prototype.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1687-1694
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• 2014

Recently FRP of carbon fibers is utilized as a repairing and reinforcing material for concrete structures. In this study, the bond performance between CFRP planks and ductile fiber reinforced cementitious composites was evaluated in order to develop a new system of concrete bridge deck to take advantage of the FRP planks of carbon fiber using as a permanent formwork. In order to strengthen the bonding between the FRP and cast-in-place concrete, an epoxy resin circulated in the market generally was fitted with a silica sand. The bond stress of ordinary concrete appeared in 2.11~5.43MPa and the bond stress of ductile fiber reinforced cementitious composites DC1 (RF4000) and DC2 (PP) respectively were 3.91~5.60MPa, 2.92~5.21MPa and the average bond stress of DC3 (RF4000+RSC15) and DC4 (PP+RSC15) were 4.80~5.58MPa, 5.57~5.89MPa.