• Journal of Power Electronics
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• v.16 no.5
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• pp.1629-1638
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• 2016

Differential power processing (DPP) systems are among the most effective architectures for photovoltaic (PV) power systems because they are highly efficient as a result of their distributed local maximum power point tracking ability, which allows the fractional processing of the total generated power. However, DPP systems require a high-efficiency, high step-up/down bidirectional converter with broad operating ranges and galvanic isolation. This study proposes a single, magnetic, high-efficiency, high step-up/down bidirectional DC-DC converter. The proposed converter is composed of a bidirectional flyback and a bidirectional isolated switched-capacitor cell, which are competitively cheap. The output terminals of the flyback converter and switched-capacitor cell are connected in series to obtain the voltage step-up. In the reverse power flow, the converter reciprocally operates with high efficiency across a broad operating range because it uses hard switching instead of soft switching. The proposed topology achieves a genuine on-off interleaved energy transfer at the transformer core and windings, thus providing an excellent utilization ratio. The dynamic characteristics of the converter are analyzed for the controller design. Finally, a 240 W hardware prototype is constructed to demonstrate the operation of the bidirectional converter under a current feedback control loop. To improve the efficiency of a PV system, the maximum power point tracking method is applied to the proposed converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.4
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• pp.299-306
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• 2009

Recently, although the power consumption of the flyback converter at the light load and standby power load was minimized by the burst mode operation of PWM IC, flyback converter has still the low efficiency characteristics by the high magnetizing current flowing through magnetizing inductance of transformer. This paper proposes a novel flyback converter with an improved efficiency characteristics and the reduced magnetizing current at the light load and standby power load. Prototype of the 70W multi-output flyback converter for an auxiliary power module of 50 inch PDP TV is built and the experimental results are described.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.2
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• pp.83-88
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• 2006

AC loss is one of the main research area in AC power application using high temperature superconductor(HTS), such as HTS transformer, HTS current limiter and HTS cable, because it is closely related to efficiency, economic estimation and design of power device. A lot of research for various arrangements of HTS tapes have been performed to increase a capacity of transport current because single HTS tape can not satisfy the demanded current capacity in HTS power application. In this paper, we studied magnetization loss by different several arrangements of BSCCO tapes such as Edge-to-Edge type, Face-to-Face type and Matrix type through numerical analysis by 2D-FEM and measurement. As a result, we got the result that the magnetization loss of Face-to-Face type arrangements was lower than those of other arrangement types under the conditions of the same stacking number. We think that the result was due to shield effect by demagnetization of adjacent HTS tapes which are located face to face.

• Proceedings of the KIEE Conference
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• 2002.04a
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• pp.158-163
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• 2002

최근 전자통신기기의 급속화된 발전과 함께 전자부품에 대한 초소형화, 고성능화가 요구되고 있다. 특히 노트북 컴퓨터나, PDA, LCD 모니터와 같이 박막 액정 표시장치(Thin Film Transistor Liquid Crystal Display, TFT-LCD)가 대표적인 예라 볼 수 있다. 이러한 박막 액정 표시장치는 그 내부에 냉음극 형광램프(Cold Cathode Fluroscent Lamp)가 있어서 백라이트의 역할을 하는데 냉음극 형광램프의 특성상 초기 고압의 구동전압을 인가시킬 수 있는 인버터가 필수적이라 하겠다. 본 논문에서는 18인치(4_CCFL), 20인치(6_CCFL) TFT-LCD 모니터용, 멀티램프 구동 인버터를 설계 제작하여 90%에 가까운 효율을 얻었다. 코일손실 및 전자유도의 장애가 없고 불연성의 장점을 가지고, 소형화가 가능한 적층형 압전 변압기를 제작하고 이 제작된 적층형 압전 변압기의 전기적 특성분석을 통한 방전램프 구동용 인버터의 승압용 변압기로써 적용이 가능함을 확인하였다.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.194-196
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• 2002

액정표시장치(LCD; Liquid Crystal Display)는 표현된 정보를 가시화하기 위해 램프의 백라이트가 필수적인데 대부분 부피가 작고 효율과 휘도특성이 좋은 냉음극 방전램프가 사용된다. 램프는 고압으로 구동되며 높은 전압을 얻기 위해 일반적으로 권선 변압기를 사용한다. 그러나 권선 변압기의 경우 자체의 철심이나 권선의 손실로 인하여 출력 효율의 한계가 있으며, 고압을 위해 감긴 코일은 부피를 크게 하며 무겁게 만든다 이를 해결하기 위해 변압기 자체 손실을 줄이고 소형화가 가능하며 높은 승압비을 가진 PAN-PZT계의 적층형 압전 변압기를 제작하였다. 또한 회로의 손실을 줄이기 위한 영전압 스위칭(ZVS; Zero Voltage Switching)과 그리고 LCD패널과 인버터의 불필요한 간섭현상(EMI; Electro-Magnetic Interference)을 줄일 수 있으며 소형화가 가능한 하프 브리지형 압전 인버터를 설계하였다.

• Journal of Internet Computing and Services
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• v.3 no.3
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• pp.1-9
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• 2002

The various researches are investigated for transforming byte code into objective machine code which can be implemented in the specific processor using classical compiling methods to improve the execution speed of the JAVA language. The code generation techniques using pattern matching can generate more high-quality code than code expansion techniques. We provide, in this research, the standardized pattern describing methods and pattern matching techniques that can be used to generate the register-based inter-language which is for the effective native code generation from byte code. And we designed and realized the inter-code transformer with which we can generate the high-quality register-based inter-code using standardized pattern described formerly.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.10
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• pp.509-516
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• 2001

Isolated phase bus(IPS) has a special structure for carrying large current generated by a generator to a main transformer. In the analysis of IPB, the understanding of the magnetic field distribution generated by large current is important. Especially, while the bus conductor current is flowing, almost same amount of current as bus conductor current is induced in the enclosures under the influence of time varying magnetic field, and therefore the large electric loss and the deterioration of insulating capability might occur due to Joule heating effect. Hence for the optimal design of IPB satisfying the condition to minimize the loss, the accurate analysis of magnetic field distribution and the eddy current characteristics of three phase isolated phase bus have been investigated. In the analysis of time varying magnetic field, instead of finite difference method(FDM) which is generally used, finite element method with phasor concept is investigated under the assumption that the bus current is purely sinusoidal. The characteristics is studied along the phase angle by comparing the effect of eddy current on the magnetic field distribution with the case that eddy current is not considered, and also the effect of material, thickness and radius of enclosure on the eddy current distribution is discussed.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.12
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• pp.514-521
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• 2006

The existing ULTC operation control strategy based on the measured data deteriorates the voltage compensation capability making the efficient corresponding to the load variation difficult by following the fixed load center point voltage. Accordingly, this paper proposes a new on-line fuzzy ULTC controller based on the designed multiple load center points which can improve the voltage compensation capability of ULTC and minimize voltage deviation by moving in real-time the load center point according to the load variation to an adequate position among the multiple load center points designed using the clustering technique. The Max-Min distance technique is adopted as the clustering technique for the decision of multiple load points from measured MTr load current and PTr voltage, and the minimum distance classifier is adopted for the decision of fuzzy output membership function. To verify the effectiveness of the proposed strategy, Visual C++ MFC-based simulation environments is developed. Finally, the superiority the proposed strategy is proved by comparing the fuzzy ULTC operation control results based on multiple load center points with the existing ULTC operation control results based on fixed load center point using the data for three day.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.153-156
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• 2001

The transformer and the OF cable are cooled and insulated by insulating oils in their body. The insulating oil expands or contracts with the heat transfer according to the operating conditions of the electric facilities. So we install the $N_2$ gas tank connected with the insulating oil system to overcome the change. The change of the insulating oil volume for the operation temperature range must be calculated to decide the $N_2$ gas volume and to set the alarm point for safe operation. It is known that this change is proportional to the temperature change and to the insulating oil volume if the temperature change is small enough.[1][11] However this proportional formula has been accepted generally in the design of electric facilities for wide operation temperature range such as $40^{\circ}C{\sim}125^{\circ}C$. Hence, it makes large errors in calculation which car result in serious damage against safe operation of the electric facilities. This paper presents a improved method of calculating the accurate change of the insulating oil volume to insure the safe operation of electric facilities.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1591-1599
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• 2017

In power electronics applications which switching frequency is below audible frequency, the acoustic noise and vibration design of magnetics are as important as the efficiency. In the case of the powder core, which is widely used in grid-connected inverters, many researches have been progressed in terms of efficiency. However, there are only few research have been progressed related with acoustic noise and vibrations. In this paper, the Sendust(Fe-Si-Al) powder core material which has low magnetostriction and low core loss is analyzed in terms of acoustic noise and vibration induced by Maxwell force and magnetostriction. Three building structures such as, rectangular, toroidal, and oval shape are designed for 4kW grid-connected inverter, because magnetic properties and the audible noises of the inductor are varied by magnetic core building structures. The effects of the Maxwell force and magnetostriction behaviors varied with core shapes are analyzed by finite element method and experiments. In addition, experiment results of the inductor efficiency are presented according to core building structures.