• 한국통신학회논문지
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• 제38A권6호
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• pp.520-527
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• 2013

본 논문에서는 클러스터 이기종 셀룰러 네트워크에서 반동적 셀 그룹핑을 위한 합동 셀 그룹핑 및 사용자 접속 기법을 제안한다. 최근에는 핫스팟에서의 폭발적인 데이터 요구량을 지원하기 위해서, 소형 셀들이 기존의 매크로 기지국들과 함께 설치되고 있다. 이러한 클러스터 이기종 셀룰러 네트워크에서는 간섭과 부하 불균형으로 인하여 성능 열화가 발생할 수 있다. 본 논문에서 제안하는 기법은 사용자들의 비례공평이 최대화되도록 두 가지 문제를 합동적으로 다룬다. 모의실험을 통하여, 기존의 기법들보다 제안하는 기법을 통해 훨씬 더 향상된 사용자 평균 전송률 및 사용자간의 비례공평을 얻을 수 있음을 알아본다.

• 태양에너지
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• 제17권1호
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• pp.27-33
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• 1997

최근 태양전지, 연료전지를 이용한 새로운 발전시스템이 개발중에 있다. 특히 소규모 분산형 계통연계 태양광발전시스템은 가까운 장래에 폭 넓게 보급될것으로 예상된다. 태양전지 어레이를 계통선과 결합하는데 사용되는 인버터는 전체 태양광발전시스템의 성능을 결정하는 중요한 요소이다. 본 논문에서는 고조파를 포함한 무효전력 보상능력을 갖는 단상 태양광 인버터 시스템의 설계 및 제어기법을 제시하였다. 제안된 인버터 시스템에 의해 정류기 부하에 의해 발생된 무효전력이 보상될 수 있음을 실험결과로 보여준다.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2011년도 추계학술발표대회 논문집
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• pp.239-244
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• 2011

In this paper, we analyzed the electrical characteristics with crack pattern in crystalline solar cell. crystalline solar cells with a thin substrate, even small shocks can be easily damaged. Before the module goes through many processes, because the solar cells are at risk of a crack. That occurred early in the PV module micro-crack is not easily detection by eye test or output test. Because the EL (Electroluminescence) device has been detected using. PV module is made by laminated of a variety of materials. By different properties of each material will affect the crack. For this reason, the crack will grow and affect the output. And We analyzed the three crack patterns in crystalline solar cell. A growth of cracks on crystalline solar cell was interpreted by analysing generated cracks on the PV modules. Based on this interpretation, an electrical output value was calculated by mathematical modeling on electrical output characteristic with each crack patterns.

• Journal of Power Electronics
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• 제13권1호
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• pp.20-30
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• 2013

This paper presents a soft switching DC/DC converter for high voltage application. The interleaved pulse-width modulation (PWM) scheme is used to reduce the ripple current at the output capacitor and the size of output inductors. Two converter cells are connected in series at the high voltage side to reduce the voltage stresses of the active switches. Thus, the voltage stress of each switch is clamped at one half of the input voltage. On the other hand, the output sides of two converter cells are connected in parallel to achieve the load current sharing and reduce the current stress of output inductors. In each converter cell, a half-bridge converter with the asymmetrical PWM scheme is adopted to control power switches and to regulate the output voltage at a desired voltage level. Based on the resonant behavior by the output capacitance of power switches and the transformer leakage inductance, active switches can be turned on at zero voltage switching (ZVS) during the transition interval. Thus, the switching losses of power MOSFETs are reduced. The current doubler rectifier is used at the secondary side to partially cancel ripple current. Therefore, the root-mean-square (rms) current at output capacitor is reduced. The proposed converter can be applied for high input voltage applications such as a three-phase 380V utility system. Finally, experiments based on a laboratory prototype with 960W (24V/40A) rated power are provided to demonstrate the performance of proposed converter.

• 한국통신학회논문지
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• 제19권5호
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• pp.842-856
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• 1994

광대역 종합정보 통신망 (B-ISDN)이 수용할 여러 서비스들은 다양한 지연, 지연 변화 및 셀 손실 확률 요구 사항을 가지고 있다. B-ISDN을 위한 적절한 제어 방법의 설계는 매우 중요하고 어려운 문제이다. 본 논문에서는, 그러한 다양한 요구사항을 만족하기 위하여, 지연 및 손실 우선 순위 모두를 가진 다종화 알고리즘을 제안한다. 손실 우선 순위의 구현을 위하여, 음성 셀은 폐기 불가한 셀(즉, 높은 우선 순위의 셀) 및 폐기 가능한 셀(즉, 낮은 우선 순위의 셀)로 생성됨을 가정하였다. 낮은 순위의 음성셀은 통신망내에서 혼잡이 발생하면 폐기될 수 있다. 본 셀 탈락 방법은 음성 및 데이터의 지연뿐만 아니라 셀 손실도 감소 시키는 것을 보여주고 있다. 이러한 부하 감소 방법은 광대역 종합정보 통신망의 이용율을 크게 개선 시킬 수 있을 것으로 기대된다.

• 전력전자학회논문지
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• 제25권3호
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• pp.157-161
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• 2020

High voltage gain converters are essential for distributed power generation systems with renewable energy sources, such as fuel cells and solar cells, because of their low voltage characteristics. This paper introduces a novel nonisolated DC-DC converter topology developed by combining an inverting buck-boost converter and voltage multipliers. In the proposed converter, the input voltage is connected in series with the output, and the majority of the input power is directly delivered to the load. The voltage multipliers are stacked in series to achieve high step-up voltage gain. The voltage stress across all of the switches and capacitors can be significantly reduced. As a result, the switches with low voltage ratings can be used to achieve high efficiency and low cost. To verify the validity of the proposed topology, a 360-W prototype converter is built to obtain the experimental results.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.494-513
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• 2019

A multi-channel access problem based on hypergraph model in ultra-dense small cell networks is studied in this paper. Due to the hyper-dense deployment of samll cells and the low-powered equipment, cumulative interference becomes an important problem besides the direct interference. The traditional binary interference model cannot capture the complicated interference relationship. In order to overcome this shortcoming, we use the hypergraph model to describe the cumulative interference relation among small cells. We formulate the multi-channel access problem based on hypergraph as two local altruistic games. The first game aims at minimizing the protocol MAC layer interference, which requires less information exchange and can converge faster. The second game aims at minimizing the physical layer interference. It needs more information interaction and converges slower, obtaining better performance. The two modeled games are both proved to be exact potential games, which admit at least one pure Nash Equilibrium (NE). To provide information exchange and reduce convergecne time, a cloud-based centralized-distributed algorithm is designed. Simulation results show that the proposed hypergraph models are both superior to the existing binary models and show the pros and cons of the two methods in different aspects.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.83-85
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• 2019

The use of high voltage gain converters is essential for the distributed power generation systems with renewable energy sources such as the fuel cells and solar cells due to their low voltage characteristics. In this paper, a high voltage gain topology combining cascode Inverting Buck-Boost converter and voltage multiplier structure is introduced. In proposed converter, the input voltage is connected in series at the output, the portion of input power is directly delivered to the load which results in continuous input current. In addition, the voltage multiplier stage stacked in proper manner is not only enhance high step-up voltage gain ratio but also significantly reduce the voltage stress across all semiconductor devices and capacitors. As a result, the high current-low voltage switches can be employed for higher efficiency and lower cost. In order to show the feasibility of the proposed topology, the operation principle is presented and the steady-state characteristic is analyzed in detail. A 380W-40/380V prototype converter was built to validate the effectiveness of proposed converter.

• Steel and Composite Structures
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• 제49권4호
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• pp.393-405
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• 2023

In this paper, the energy absorption capability of a novel cruciform composite lattice structure was evaluated through the simulation of compression tests. For this purpose, several test samples of Polylactic acid cellular reinforced with continuous glass fibers were prepared for compression testing using the additive manufacturing method of material extrusion. Using a conventional path design for material extrusion, multiple debonding is probable to be occurred at the joint regions of adjacent cells. Therefore, an innovative printing path design was proposed for the cruciform lattice structure. Afterwards, quasistatic compression tests were performed to evaluate the energy absorption behaviour of this structure. A finite element model based on local material property degradation was then developed to verify the experimental test and extend the virtual test method. Accordingly, different combinations of unit cells' dimensions using the design of the experiment were numerically proposed to obtain the optimal configuration in terms of the total absorbed energy. Having brilliant energy absorption properties, the studied cruciform lattice with its optimized unit cell dimensions can be used as an energy absorber in crashworthiness applications. Finally, a cellular structure will be suitable with optimal behavior in crush load efficiency and high energy absorption.

• 한국산학기술학회논문지
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• 제18권7호
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• pp.375-381
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• 2017

성토지지말뚝의 아칭효과를 실험적으로 살펴보고자 현장시험을 수행하였으며 계측결과로부터 구한 아칭효율을 이론식에 의한 값과 비교해 보았다. 성토지지말뚝의 아칭효과를 살펴보기 위해 측정한 하중계 및 토압계에 의한 계측값들은 대체적으로 성토지지말뚝의 아칭효과를 반영하였다. 하중계 측정값을 통해 볼 때 아칭효율은 성토고 3m 까지는 평면변형률 조건을 가정한 이론식에 의한 값보다 작았으나 4m 이상에서는 이론식에 의한 값보다 큰 값을 보였으며 이론식에 의할 경우, 아칭효율은 성토고에 따라 감소하는 경향을 보였으나 측정결과는 성토고에 따라 아칭효율도 증가하는 경향을 나타내었다. 현장 시험에서 계획했던 최종 성토고까지 비교적 원활하게 작동하였던 토압계에 의한 계측결과에 따르면, 성토고에 따라 평면변형률 조건을 가정한 이론식에 의한 값보다 큰 아칭효율을 나타내었으며 4m 이상의 성토고에 대해서는 아칭효율의 변화양상 또한 이론식과 유사한 경향을 보였다. 토압계 측정결과에 따르면 성토고 2m, 3m, 4m, 5m 그리고 6m일 때의 아칭효율은 평면변형률조건을 가정한 이론식에 의한 아칭효율에 비해 각각 1.05배, 1.23배, 1,29배, 1.28배 그리고 1.29배 큰 값들을 보여 우수한 아칭효과를 보임을 알 수 있었다. 현장시험을 통해 얻은 하중계 및 토압계 측정값들로부터 계산된 아칭효율은 말뚝을 격자배치한 경우에 대한 이론식에 의한 그것보다 상당히 컸다.