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황동현(Dong-Hyeon Hwang),이우철(Woo-Cheol Lee) 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.1
A non-inverting buck-boost converter is used to keep the output voltage constant if the range of variation of the input voltage is lower or higher than the desired output voltage. It has a wide input/output voltage range and the output voltage is not inverted unlike a typical buck-boost converter. The non-inverting buck-boost converter is classified into continuous current mode, discontinuous current mode, and critical conduction mode depending on the inductor current. The losses of the switching device depends on the current modes and the efficiency of converter is also different. Therefore, in this paper, the converter is controlled by the fixed frequency method and the critical conduction mode method to compare the converter efficiency according to the current modes at low power. In each control method, the losses of the switching element were calculated and compared. Simulation and experiment were performed to confirm the calculated results.
태양전지 전압 탐색기법을 이용한 전역 최대전력 점 추종 방법
황동현(Dong-Hyeon Hwang),이우철(Woo-Cheol Lee) 한국조명·전기설비학회 2018 조명·전기설비학회논문지 Vol.32 No.3
When a partial shading occurs in a solar cell, a plurality of maximum points appear in the output characteristic, so that the general maximum power point tracking method can not track the actual maximum point. In order to overcome this problem, several studies have been conducted on the technique of tracking the actual maximum point under partial shading. However, the methods to follow the actual maximum points studied also have disadvantages in that they do not follow the actual maximum power point in all conditions or require additional circuitry. In this paper, we propose an algorithm that can always follow the actual maximum power point without any additional circuit under partial shadow, and verify the proposed algorithm through simulation and experiment.
황동현(Dong Hyeon Hwang),이창식(Chang Sik Lee),이기형(Ki Hyung Lee),최서원(Seo Won Choi) 한국자동차공학회 1995 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1995 No.6_1
The purpose of this paper is to show the performance charateristics of Roots type supercharger with two lobe rotor. The performance test were conducted to obtain the drive power, volumetric efficiency, and the influence performance factors of supercharger. With the flow characteristics of supercharger, the effect of the operating conditions on supercharger performance was investigated. The results show that the increase of supercharger speed and pressure ratio bring about the increase of drive power.<br/>
부스트 컨버터를 이용한 태양전지 어레이 전역 최대전력점 추종 방법
황동현(Dong-Hyeon Hwang),이우철(Woo-Cheol Lee) 대한전기학회 2018 전기학회논문지 Vol.67 No.2
Since solar cells have non-linear voltage-current output characteristics, Photovoltaic systems require the Maximum Power Point Tracking(MPPT) function. For this reason, a large number of MPPT techniques have been studied. However, the conventional MPPT techniques may fail to track the maximum power point when partial shading occurs in the solar cell array due to its characteristics. Therefore, it is necessary to research the MPPT technique that can follow the maximum power point in the partial shadow condition. In this paper, the characteristics of solar cell arrays in partial shadowing are analyzed and the MPPT technique which can follow the maximum power point in partial shadow condition has been proposed. To validate the proposed MPPT method, simulation and experimentation results are provided.
A7075-T6 알루미늄 합금의 프레팅 피로 손상 파라미터 비교 평가
황동현(Dong Hyeon Hwang),조성산(Sung-San Cho) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.10
신뢰성이 가장 우수한 프레팅 피로손상 파라미터를 찾아내기 위해 알루미늄 합금 A7075-T6 을 대상으로 피로시험을 수행하였다. 시편 표면에 홈을 가공하여 패드 접촉압력에 따라 패드-시편 접촉면에서프레팅 피로균열이 발생하거나 또는 홈에서 일반 피로균열이 발생할 수 있게 하였다. 광학현미경을 이용하여 균열의 발생위치와 방향을 측정하고, 문헌에서 가장 많이 사용되는 프레팅 피로손상 파라미터들의 신뢰성을 평가하였다. 파라미터 값과 최대손상평면 방향을 산출하는데 필요한 응력과 변형률 자료는 유한요소해석으로 산출하였다. 전단모드 피로파손을 가정하는 Fatemi-Socie 파라 미터와 McDiarmid 파라미터가 가장 신뢰성이 높은 것으로 판명되었다. Fatigue tests were conducted on the aluminum alloy, A7075-T6 to determine the most reliable fretting fatigue damage parameter. Specimens with grooves were used, so that either fretting fatigue crack at the pad/specimen interface or plain fatigue crack at the groove could be nucleated, depending on the pad pressure. Both the crack nucleation location and initial crack orientation were examined using optical microscopy, and the results were used to assess the reliability of the various fretting fatigue damage parameters that have been most commonly used in the literature. Finite element analysis was employed to obtain the stress and strain data of the specimen, which were needed to estimate the parameter values and the orientation of the critical plane. It was revealed that both the Fatemi?ocie and McDiarmid parameters, which assume shear-mode fatigue cracking, are the most reliable.