• Journal of Power Electronics
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• 제16권1호
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• pp.173-181
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• 2016

In this paper, a new technique for harmonic optimization in cascaded H-bridge 7-level inverters is proposed. The suggested strategy is based on minimizing an objective function which simultaneously optimizes the converter utilization and Total Harmonic Distortion (THD). The Switch Utilization Ratio (SUR) is formulized for both the phase and line-line voltages of a 7-level inverter and is considered in the final objective functions. Based upon the SUR formula, utilization ratio enhancement will reduce the value of feeding DC links, which improves the efficiency and lifetime of the circuit components due to lower voltage stresses and losses. In order to achieve more effective solution in different modulation indices, it is assumed that the DC sources can be altered. Experimental validation is presented based on a three-phase 7-level inverter prototype.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권11호
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• pp.3680-3693
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• 2022

The handover procedure of IEEE 802.11 wireless local area networks (WLANs) introduces significant delay, which can degrade the quality of service (QoS) especially for delay-sensitive applications. Although studies have been conducted to support handover in SDN-based WLAN, there is no research to reduce the channel scanning procedure that takes up the most delay time in the handover process. The channel scanning procedure is essential to determine the appropriate access point (AP). To mitigate this problem, this paper proposes a SWITCH: SDN-WLAN integrated handover scheme for QoS-Guaranteed mobile service. In SWITCH, each AP periodically broadcasts beacon frames through different channels in a predetermined order that includes the operating channel information of the AP. This allows mobile stations (MSs) to receive the beacon frames of nearby APs, and therefore they can determine the appropriate APs for handover without the channel scanning procedure. By reporting the information of the newly moved AP to the SDN controller, a flow rule is installed in advance to provide fast handover, and packet loss is reduced by buffering data destined for MS. In addition, the proposed scheme can adaptively operate SWITCH to consider the user location and QoS requirement of flow to save radio resource overhead. Performance evaluation results demonstrate that SWITCH can reduce the handover delays, flow table utilization ratio and radio resource overhead while improving the network throughput.

• 한국정보처리학회논문지
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• 제6권3호
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• pp.742-749
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• 1999

This paper proposes the mechanism of cell buffering in the output buffer of ATM switch for the traffic with the different QOS in the ATM environment. The proposed mechanism, VQS(Variable Queue Sharing) can minimize the cell loss ratio(CLR) of bursty traffic through the sharing of CBR queue, VBR queue, ABR queue to maximize the utilization of queue resource. To evaluate VQS performance, we make simulator using Visual Slam 2.0. We compare the CLP and cell average delay of VQS and HOL, QLT_HOL using the bursty traffic patterns.

• 융복합기술연구소 논문집
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• 제4권1호
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• pp.15-20
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• 2014

Recently, the development of renewable energy sources in Korea has been needed due to climate change. One of powerful alternative energy resources to mitigate emission is to switch conventional fuels to renewable energy, such as bioenergy. In this study, current status of bioenergy conversion technology and its supply in Korea was investigate. Based on theoretical, technical and realizable potential of biomass in Korea, the amount of reduction of green house gases was estimated. The results shown that the contribution of biomass on 2020 reduction target of green house gases emission in power generation was $513,000\;tCO_2/yr$ and utilization ratio of technical potential of biomass was 6.4%. For the effective supply of bioenergy in Korea, more exact estimation of realizable potential of biomass in Korea and stable supply sources are needed.

• 한국컴퓨터산업학회논문지
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• 제3권1호
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• pp.19-26
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• 2002

다양한 QoS를 갖는 트래픽을 위해, ATM 스위치의 출력버퍼에 저장되는 셀의 큐 구조를 제안하였다. 제안한 큐 구조는 기존의 고정길이 큐 구조의 문제점인 버스트 트래픽으로 인한 큐 넘침의 문제점을 개선하기 위해 실시간 트래픽과 비실시간 트래픽을 묶어 큐를 공유하여 큐 이용률을 최대화시키는 구조를 기반으로 하고 있다. 즉, CBR 트래픽과 VBR-nrt를 묶고, VBR-rt와 ABR 트래픽을 묶어 버스트 트래픽 유입으로 인한 셀 손실률을 최소화시킬 수 있는 특성을 제공한다. 제안 큐 구조의 성능을 평가하기 위해 버스트 특성이 강한 트래픽 패턴을 이용하여 기존의 큐 구조와 셀 손실률 및 평균 지연률을 비교하였다.

• 한국항만경제학회지
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• 제31권4호
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• pp.121-132
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• 2015

양산 ICD(Inland Container Depot)는 2000년 3월 개장 이후 2005년 133만 TEU를 처리하여 국제물류경쟁력과 부산지역의 컨테이너화물 운송 경쟁력을 높여 부산항 및 우리나라 항만물류산업에서 중요한 역할을 담당하였다. 그러나 2006년 부산항 신항 개장과 신항배후부지의 조성에서 물동량이 급감하여 활성화를 위한 새로운 방안이 모색이 필요한 상황이다. 따라서 본 연구는 AHP(analytic hierarchy process)를 활용하여 평가모형을 설정하고, 양산 ICD 내 입주기업 및 관계자를 대상으로 설문조사를 실시하여 양산 ICD의 활성화 방안을 모색하였다. 연구의 결과, 양산 ICD 활성화 방안으로 입지와 시설의 장점을 고려한 물류시설(공동집배송센터, 물류창고)로의 기능전환이 필요하며, 이용기간 연장, 건폐율 확보를 통해 기존 및 신규 기업활동의 안정성을 보장하여야 할 것이다. 또한 ICD 내 철도역 등 시설을 활용하여 적극적인 철도활성화 정책을 통해 철도택배 등을 활용하여 신규 물동량을 창출하고, 공로 중심의 국가물류체계에서 철송 활성화를 통한 내륙물류기지로서의 그 역할을 제시하였다.

• 한국항해항만학회지
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• 제47권2호
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• pp.106-119
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• 2023

Due to global decarbonization movement and tightening of maritime emissions restrictions, the shipping industry is going to switch to alternative fuels. Among candidates of alternative fuel, methanol is promising for decreasing SOx and CO2 emissions, resulting in minimum climate change and meeting the goal of green shipping. In this study, a novel combined system of direct methanol solid oxide fuel cells (SOFC), proton exchange membrane fuel cells (PEMFC), gas turbine (GT), and organic Rankine cycle (ORC) targeted for marine vessels was proposed. The SOFC is the main power generator of the system, whereas the GT and PEMFC could recover waste heat from the SOFC to generate useful power and increase waste heat utilizing efficiency of the system. Thermodynamics model of the combined system and each component were established and analyzed. Energy and exergy efficiencies of subsystems and the entire system were estimated with participation of the first and second laws of thermodynamics. The energy and exergy efficiencies of the overall multigeneration system were estimated to be 76.2% and 30.3%, respectively. The combination of GT and PEMFC increased the energy efficiency by 18.91% compared to the SOFC stand-alone system. By changing the methanol distribution ratio from 0.05 to 0.4, energy and exergy efficiencies decreased by 15.49% and 5.41%, respectively. During the starting up and maneuvering period of vessels, a quick response from the power supply system and propulsion plant is necessary. Utilization of PEMFC coupled with SOFC has remarkable meaning and benefits.