• Journal of Electrical Engineering and Technology
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• 제10권5호
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• pp.1989-2000
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• 2015

In this paper, digital peak current mode control for single phase H-bridge inverters is developed and implemented. The digital peak current mode control is achieved by directly controlling the PWM signals by cycle-by-cycle current limitation. Unlike the DC-DC converter where the output voltage always remains in the positive region, the output of DC-AC inverter flips from positive to negative region continuously. Therefore, when the inverter operates in negative region, the control should be changed to valley current mode control. Thus, a novel control logic circuit is required for the function and need to be analyzed for the hardware to track the sinusoidal reference in both regions. The problem of sub-harmonic instability which is inherent with peak current mode control is also addressed, and then proposes the digital slope compensation in constant-sloped external ramp to suppress the oscillation. For unipolar PWM switching method, an adaptive slope compensation in digital manner is also proposed. In this paper, the operating principles and design guidelines of the proposed scheme are presented, along with the performance analysis and numerical simulation. Also, a 200W inverter hardware prototype has been implemented for experimental verification of the proposed controller scheme.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.223-225
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• 2008

In order to apply SFCLs into electric power systems, the urgent issues to be settled are as follows, such as initial installation price, operation and maintenance cost due to ac loss of superconductor and the life of cryostat, and high voltage and high current problems. We designed novel hybrid SFCLs which combine superconductor and conventional electric equipments including a vacuum interrupter, an electro-magnetic contactor and a current limiting reactor. The main purpose of the hybrid SFCL is to drastically reduce total usage of superconductor by adopting current commutation method by use of the superconductor and the fast switch. According to protective coordination and performance, we investigated two concepts of Hybrid SFCLs. First is a half cycle fault current limitation type and second is a non-half cycle fault current limitation type. We concluded that the non-half cycle fault current limitation type is batter than the other.

• 천문학회지
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• 제50권2호
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• pp.21-27
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• 2017

The autoregressive method provides a univariate procedure to predict the future sunspot number (SSN) based on past record. The strength of this method lies in the possibility that from past data it yields the SSN in the future as a function of time. On the other hand, its major limitation comes from the intrinsic complexity of solar magnetic activity that may deviate from the linear stationary process assumption that is the basis of the autoregressive model. By analyzing the residual errors produced by the method, we have obtained the following conclusions: (1) the optimal duration of the past time for the forecast is found to be 8.5 years; (2) the standard error increases with prediction horizon and the errors are mostly systematic ones resulting from the incompleteness of the autoregressive model; (3) there is a tendency that the predicted value is underestimated in the activity rising phase, while it is overestimated in the declining phase; (5) the model prediction of a new Solar Cycle is fairly good when it is similar to the previous one, but is bad when the new cycle is much different from the previous one; (6) a reasonably good prediction of a new cycle can be made using the AR model 1.5 years after the start of the cycle. In addition, we predict the next cycle (Solar Cycle 25) will reach the peak in 2024 at the activity level similar to the current cycle.

• 한국BIM학회 논문집
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• 제6권4호
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• pp.9-17
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• 2016

Currently whole-house refurbishment for substantial energy efficiency improvement of existing housing stock is needed to achieve the targeted 80% CO2 emission reduction. As whole-house refurbishment requires a larger capital investment for lower CO2 emission, the simultaneous use of Life Cycle Costing (LCC) and Life Cycle Assessment (LCA) methodologies are recommended to generate affordable refurbishment solutions. However, two methodologies are difficult to use due to a lack of proper LCC and LCA datasets. As a response to the current problems, many researchers explore potentials in Building Information Modelling (BIM) to improve current construction practice. As a result, a BIM tool - IES IMPACT (Integrated Material Profile And Costing Tool) - has been introduced to the UK construction industry for simultaneous calculation of LCC and LCA. Thus, this research aims at examining the capability and limitation of the IES VE/IMPACT as a BIM tool for whole-house refurbishment. This research reveals that the IES VE/IMPACT is feasible for whole-house refurbishment by providing LCC and LCA information simultaneously for informed decision on refurbishment solution selection. This research shed lights on the current problems lying on the data exchange between two different BIM tools. It is revealed that additional efforts from construction professionals and industry are required to make reliable BIM objects library with LCC and LCA datasets.

• 한국초전도ㆍ저온공학회논문지
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• 제15권4호
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• pp.30-33
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• 2013

The studies of superconducting fault current limiter (SFCL) for reduction of the fault current are actively underway in the worldwide. In this paper, we analyzed the characteristics of a new type SFCL using the conventional transformer and superconducting elements combined mutually. The secondary and third windings of this SFCL were connected the load and the superconducting element, respectively. The electric power was provided to load connected to secondary windings of the transformer in normal state of power system. On the other hand, when the fault occurred in power system, the fault current was limited by closing the line of third winding of the transformer. At this time, the ripple phenomenon of the fault was minimized by opening the fault line in secondary winding of a transformer in power system. The sensing of the fault state was performed by the CT(current transformer) and then turn-on and turn-off switching behavior of the SFCL was performed by the SCR(silicon-controlled rectifier). As a result, the proposed SFCL limited the fault current within a half-cycle efficiently. We confirmed that the fault current limitation rate was changed according to the winding ratio of a transformer.

• 한국CDE학회논문집
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• 제15권5호
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• pp.393-402
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• 2010

Existing construction industry is composed of several processes with various characteristics. The tendency of current construction industry is getting complicated and diversified; it has limitation to solve problems through existing processes. As a problem-solving method, BIM (Building Information Modeling), environment to manage building life cycle from design and construction to management, is being suggested. Currently, BIM is only focused on technology development by engineers, and the automation of architectural theories is insufficiency except architectural design modeling. Therefore, this research aims to back up theses drawbacks through intellectual curtain wall arrangement by using musical proportions. In order to apply to construction automation, analysised of musical proportions method are performed. The BPMN-based Process Map is listed to develop IDM for the application to BIM Software.

• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1821-1833
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• 2021

The gas-liquid counter-current flow limitation (CCFL) is closely related to efficient and safety operation of many equipment in industrial cycle. Air-water countercurrent flow experiments were performed in a tube with diameter of 25 mm to understand the triggering mechanism of CCFL. A parallel electrode probe was utilized to measure film thickness whereby the time domain and frequency domain characteristics of liquid film was obtained. The amplitude of the interface wave is small at low liquid flow rate while it becomes large at high liquid flow rate after being disturbed by the airflow. The spectral characteristic curve shows a peak-shaped distribution. The crest exists between 0 and 10 Hz and the amplitude decreases with the frequency increase. The analysis of visual observation and characteristic of film thickness indicate that two flooding mechanisms were identified at low and high liquid flow rate, respectively. At low liquid flow rate, the interfacial waves upward propagation is responsible for the formation of CCFL onset. While flooding at high liquid flow rate takes place as a direct consequence of the liquid bridging in tube due to the turbulent flow pattern. Moreover, it is believed that there is a transition region between the low and high liquid flow rate.

• 한국산학기술학회논문지
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• 제21권12호
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• pp.153-161
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• 2020

스마트건설기술 중 하나인 건설정보모델은 현행 건설시설사업에 필수 기술로 인식되고 있다. 특히 건설사업 발주 기관인 조달청 등에서 BIM 전면도입 계획을 발표하였기에 설계지원용역 업무에서도 BIM설계 정보를 활용한 업무추진이라는 변화가 요구되고 있다. LCC분석은 공사내역서상의 아이템, 물량, 비용 정보가 필수 정보이므로 BIM설계 정보 활용에 따른 업무 효율성과 시간단축이 기대되는 분야이다. 이에 본 연구에서는 개방형 KBIMS 라이브러리를 적극 활용하여 최적설계 대안 선정용 BIM-LCC분석 시스템을 구축하였다. 설계안의 적정성과 최적설계안을 선정하기 위하여 단일대안과 최적대안 LCC분석 기능을 구현하였으며, LCC분석과 기능분석을 실시하여 가치가 높은 대안을 선택할 수 있는 기능도 포함하였다. 그러나 BIM-LCC분석 시스템은 국토교통부에서 개방형 BIM을 위해 공개한 건축과 기계 라이브러리만을 적용했다는 한계점을 가지고 있으나 BIM기술을 적용했다는 점에서 실무 활용성과 업무 효율성을 기대할 수 있다. 향후 설계단계 BIM설계정보를 활용한 LCC분석 지원 툴로서 활용하기 위해 다양한 테스트베드를 선정하여 해당 시스템을 검증하고, 실무적용성 및 UI개선, 신규로 추가되는 라이브러리에 대한 LCC기준 DB화 방안에 대한 검토가 필요하겠다.

• 지구물리와물리탐사
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• 제25권4호
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• pp.227-241
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• 2022

전파형 역산은 석유가스 탐사를 위한 탄성파 자료처리 분야에서 지층의 속도 모델을 추정하는데 사용되는 역산 기법이다. 최근 탄성파 자료처리에 딥러닝 기술의 활용이 급격하게 증가하고 있는데, 전파형 역산 기술도 마찬가지로 다양한 연구가 이루어지고 있다. 초기에는 머신러닝 기술을 활용한 자료처리 기법이 전파형 역산을 위한 입력자료의 전처리 목적으로 활용되는 수준이었으나, 딥러닝 기술을 통해 전파형 역산을 직접적으로 구현하는 연구가 등장하기 시작하였다. 딥러닝 기술을 활용한 전파형 역산은 순수 데이터 기반 접근법, 물리 기반 신경망 활용법, 인코더-디코더 구조 활용법, 신경망 재매개변수화를 이용한 구현법, 물리정보 기반 신경망 기법 등으로 구분할 수 있다. 이 논문에서는 딥러닝 기반 전파형 역산 기법을 발전 과정 순서로 체계화하여 각각의 접근법에 대한 이론과 특징을 설명하였다. 전파형 역산 기술에 딥러닝 기법을 도입한 초기에는 데이터 과학의 기본 원리에 충실하게 대량의 학습자료를 준비하고 순수 데이터 기반 예측 모델을 적용하여 속도 모델을 역산하는 연구로 시작하였다. 최근 연구 동향은 탄성파 자료의 잔차나 파동방정식 자체의 물리정보를 심층 신경망에 활용하여 순수 데이터 기반 접근법의 단점을 보완해 나가는 방향으로 진행되고 있다. 이러한 발전으로 대량의 학습자료가 필요하지 않고, 전파형 역산의 태생적 한계점인 주기 놓침 현상을 완화하며 계산 시간을 획기적으로 줄일 수 있는 딥러닝 기반 전파형 역산 기술이 등장하고 있다. 딥러닝 기술의 도입으로 전파형 역산 기술은 탄성파 자료처리 분야에서 가치가 더 높아질 것으로 생각된다.

• 기록학연구
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• 제13호
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• pp.135-178
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• 2006

정보제공에 대한 공공기관의 대응은 기록관리의 정비가 정보공개제도의 시행에 앞서 실천되어야 할 중요한 과제라는 것을 확인시켜 주었다. 특히, 주요 정보가 포함된 기록에 대한 공공기관의 정보 부존재, 비공개 및 비밀 처분의 남발은 공공기관에서의 기록관리에 대한 전반적인 의식변화는 물론 비공개나 비밀로 관리되는 기록에 대한 근본적인 개선이 시급함을 보여주었다. 본 연구는 이러한 문제의식에 근거하여 현재의 비공개 및 비밀기록 관리의 실태를 검토하고 이에 대한 개선방안을 제안하였다. 지금까지 비공개 및 비밀기록에 대한 연구는 법적,행정적 관점에서만 논의가 진행되어 주로 제도적인 측면만이 부각되었다. 그러나 이러한 논의는 비공개 및 비밀기록의 문제에 대한 본질적인 접근이 되지 못하는 한계가 있다. 비공개 및 비밀로 분류되는 정보는 결국 기록이 생산되는 시점부터 관리까지의 모든 프로세스가 합리적으로 수행되어야만 근본적인 개선이 이루어 질 수 있기 때문이다. 따라서 본 연구에서는 우리의 기록관리체계가 처리과, 자료관, 전문관리기관이라는 세 단계로 구분되어 기록의 라이프사이클 흐름을 적용하여 관리할 수 있는 방식을 취하고 있는 만큼 이러한 단계에 따라 비공개 및 비밀기록의 생산부터 활용에 이르기까지의 전반적인 문제를 살펴보고 그에 대한 개선방향을 제시하였다.