• Journal of Power Electronics
• /
• v.19 no.2
• /
• pp.431-442
• /
• 2019

This paper proposes a unified high-frequency bipolar buck-boost (UHFBB) control strategy for a dual-active-bridge (DAB), which is derived from the classical buck and boost DC/DC converter. It can achieve optimized current stress of the switches and soft switching in wider range. The UHFBB control strategy includes multi-control-variables, which can be achieved according to an algorithm derived from an accurate mathematical model. The design method for the parameters, such as the transformer turns ratio and the inductance, are shown. The current stress of the switches is analyzed for selecting an optimal inductor. The analysis is verified by the experimental results within a 500W prototype.

• Electronics and Telecommunications Trends
• /
• v.37 no.1
• /
• pp.53-62
• /
• 2022

With increasing size of transformer-based neural networks, a light-weight algorithm and efficient AI accelerator has been developed to train these huge networks in practical design time. In this article, we present a survey of state-of-the-art research on the low-precision computational algorithms especially for floating-point formats and their hardware accelerator. We describe the trends by focusing on the work of two leading research groups-IBM and Seoul National University-which have deep knowledge in both AI algorithm and hardware architecture. For the low-precision algorithm, we summarize two efficient floating-point formats (hybrid FP8 and radix-4 FP4) with accuracy-preserving algorithms for training on the main research stream. Moreover, we describe the AI processor architecture supporting the low-bit mixed precision computing unit including the integer engine.

• KEPCO Journal on Electric Power and Energy
• /
• v.8 no.2
• /
• pp.87-92
• /
• 2022

Recently, there has been an increasing demand for electric equipment installed on the ground to be installed in an underground space. Accordingly, U-CDS (Underground-Compact Distribution Station) installed in the underground is supplied, and to improve its weak ventilation performance, an Airdam-type structure was applied and the effect was analyzed. As a result, the temperature around the transformer was reduced by up to 9.5 degrees, and the air flow increased by up to 1.17 m/s. Airdam structure can be supplied in the form of various sculptures because it is possible to design freely while maintaining its principle.

• The Journal of Information Systems
• /
• v.31 no.4
• /
• pp.01-23
• /
• 2022

Purpose This study aims to propose a deep learning-based fake review detection model by combining authors' linguistic features and semantic information of reviews. Design/methodology/approach This study used 358,071 review data of Yelp to develop fake review detection model. We employed linguistic inquiry and word count (LIWC) to extract 24 linguistic features of authors. Then we used deep learning architectures such as multilayer perceptron(MLP), long short-term memory(LSTM) and transformer to learn linguistic features and semantic features for fake review detection. Findings The results of our study show that detection models using both linguistic and semantic features outperformed other models using single type of features. In addition, this study confirmed that differences in linguistic features between fake reviewer and authentic reviewer are significant. That is, we found that linguistic features complement semantic information of reviews and further enhance predictive power of fake detection model.

• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.19-21
• /
• 2020

본 논문은 OBC의 전력 밀도를 향상시키기 위한 LLC용 planar 변압기의 설계 방법을 제안한다. 이를 위해 상용 planar 변압기 코어를 사용한 OBC를 바탕으로 planar 변압기 코어 최적 파라미터와 패턴 배치에 따른 영향을 FEM 시뮬레이션을 통해 설계하고 분석한다. 분석 결과를 바탕으로 설계된 planar 변압기를 3.3 [kW]급 LLC 컨버터 prototype을 통해 검증한다.

• Proceedings of the KIPE Conference
• /
• 2020.08a
• /
• pp.296-297
• /
• 2020

변압기의 크기와 누설 인덕턴스는 각각 위상천이 풀-브릿지 컨버터의 전력 밀도와 영전압 스위칭의 동작 범위에 영향을 준다. 따라서 본 논문에서는 컨버터의 전력 밀도 및 효율향상을 위한 변압기의 설계에 대해 이론적으로 분석하고, 이를 시작품으로 만들어 5.6kW급 컨버터를 통해 실험적으로 검증하였다.

• Journal of Power Electronics
• /
• v.13 no.2
• /
• pp.206-213
• /
• 2013

In this paper, an improved passive snubber is investigated in a single-phase single-stage full-bridge boost power factor correction (PFC) converter, by which the voltage spike across primary side of the power transformer can be suppressed and the absorbed energy can be transferred to the output side. When compared with the basic passive snubber, the two single-inductors are replaced by a coupled-inductor in the improved snubber. As a result, synchronous resonances in the snubber can be achieved, which can avoid the unbalance of the voltage and current in the snubber. The operational principle of the improved passive snubber is analyzed in detail based on a single-phase PFC converter, and the design considerations of both the snubber and the coupled-inductor are given. Finally, a laboratory-made prototype is built, and the experimental results verify the feasibility of the proposed method and the validity of the theoretical analysis and design method.

• Journal of Institute of Control, Robotics and Systems
• /
• v.20 no.2
• /
• pp.143-148
• /
• 2014

Conventional wireless power transfer methods based on coupled magnetic fields need a complex winding structure on the surface of the energy transfer and shows poor efficiency near metal objects due to the eddy current effect. In this study, to mitigate these problems, we investigate an electric field-coupled power transmission system, which is less prone to metal object problems and EMI. Because of the fundamental physical limit in the size of link capacitances, a half-bridge converter with an impedance matching transformer is proposed and the design procedure is derived to provide a soft-switching scheme. Hardware implementation shows that the proposed scheme with a pair of 10cm by 10cm copper plate can power a 1.4W USB FAN in a separation of 0.2mm by using insulating paper when driven by 227 kHz gate pulse.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.11 no.5
• /
• pp.103-115
• /
• 2012

In this paper, design and performance evaluation of Tapered Slot Antenna for IR-UWB which propagates impulse radio is performed. TSA which has directional characteristic in UWB band should have low radiation loss and minimized impulse radiation distortion. In order to achieve these objectives, the paper designed wide band Impedance transformer and microstrip-slotline transit region structured TSA feeder line. By using the fabricated TSA, the radiation pattern was measured in the radio anechoic chamber. Pulse fidelity and distortion equation was induced to evaluate time domain characteristics according to the impulse radiation. Pulse fidelity of Impulse radiation show favorable results more than 93% within ${\pm}30^{\circ}$ beam width.

• Journal of the Korean Society of Industry Convergence
• /
• v.15 no.1
• /
• pp.5-11
• /
• 2012

The Buckling of the member under compressive stress is likely to occur, which is an important factor determining the strength of structures. The objective of this study was to evaluate the member buckling strength of a circular hollow steel with ball joints and to compare with design specifications for load resistance factor of our country. Furthermore, we would like to suggest basic data for evaluation of buckling length of a circular hollow steel with ball joints according to comparative analysis. These results were summarized as follows: Buckling stress according to the test results on buckling was 1.21 times greater than LSD specifications of our country estimated the entire length of circular hollow steel with ball joints as buckling length. In addition, it was 1.16 times greater than when estimating the length except the ball as buckling length and 1.14 times grater than when excluding the ball and sleeve. Therefore, when estimating buckling stress of circular hollow steel with ball joints, their buckling length may be measured by the length except ball and sleeve.