• Journal of Power Electronics
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• 제18권3호
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• pp.681-693
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• 2018

This paper proposes a soft-switching bidirectional dc-dc converter (BDC) with an auxiliary circuit. The proposed BDC can achieve the zero-voltage switching (ZVS) using an auxiliary circuit in the buck and boost operations. The auxiliary circuit supplies optimal energy for the ZVS operation of the main switches. The auxiliary circuit consists of a resonant inductor, a back-to-back switch and two capacitors. A small-sized resonant inductor and an auxiliary switch with a low-rated voltage can be used in the auxiliary circuit. Zero-current switching (ZCS) turn-on and turn-off of the auxiliary switches are possible. The proposed soft-switching scheme has a look-up table for optimal switching of the auxiliary switches. The proposed strategy properly adjusts the turn-on time of the auxiliary switch according to the load current. The proposed BDC is verified by the results of PSIM simulations and experiments on a 3-kW ZVS BDC system.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제5B권4호
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• pp.343-349
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• 2005

This paper proposes a novel zero-voltage-switching (ZVS) Push-pull DC-DC Converter for high input voltage and high power applications. This topology utilizes two switches in series to replace one switch in conventional push-pull converter, and two clamping diodes are introduced. The voltage stress of the switches is the input voltage, and the switches can realize ZVS with the use of the leakage inductance of the transformer. Furthermore, secondary full-wave rectifier with a clamping capacitor is used to eliminate the voltage oscillation and spike of the rectifier diodes due to the reverse recovery. Therefore, the electromagnetic interference is reduced effectively. The operation principle of the proposed converter is analyzed theoretically. The output characteristic, ZVS condition and design principle of the clamping capacitor are discussed. Experimental results obtained from a 270V input 2kW prototype with $95.8\%$ high efficiency confirms the design.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 F
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• pp.2036-2038
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• 1998

In the buck-boost DC-DC chopper which is used at a certain situation such as in factories where loads often change a lot, the switches in the device make big energy loss in operating at Buck-Boost Mode due to hard switching and are affected by lots of stresses which decrease the efficiency rate of the converter. In order to improve this problem, to decrease the loss of snubber and switching, it has been investigated that zero voltage switching mode and zero current switching mode which make the operation of switches with soft switching. For the more sophisticated and advanced device, this paper is presented the Partial Resonant Soft Switching Mode Power Converter which is adapted the power converter having the partial resonant soft switching mode, that makes switches operate when the resonant current or voltage becomes zero by making the resonant circuit partially at turning on and off of the switches with suitable layout of the resonant elements and switch elements in the converter. Also, this paper includes the analysis and simulation of the Partial Resonant type Buck-Boost Chopper.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.183-185
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• 1994

A new method for determination of electric parameter of cell membranes is proposed. Two circular electrodes is designed to have repulsive force. From the potential energy analysis, stable points where a cell is levitated between electrodes exist and move as frequency or voltage change. The levitated cell in the stable point fall freely when DEP force is zero. The DEP force is dependent on the frequency and the force is zero at the critical frequency. The critical frequency is determined by measuring the difference between the time taken at zero-applied voltage and the time taken at the frequency and the voltage. For example, the critical frequency and stable points of N.crassa slime cell is numerically evaluated. In the exeriment, polystyrene in water is levitated at the stable point. We show that the stable point move as the applied voltage is changed.

• 대한토목학회논문집
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• 제7권4호
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• pp.83-90
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• 1987

본 연구에서는 Mindlin 평판요소의 개선을 위하여 사용되고 있는 감차적분방법과 비적합 변위형의 추가방법에 대한 재검토가 이루어졌으며, 이 두방법을 혼합 사용하여 개발한 새로운 평판유한요소가 제시되었다. 요소는 2차 Mindlin 평판이론에 의하여 수식화되었다. 개발된 평판요소를 이용하여 구한 수치해석 결과는 이론치에 매우 빨리 수렴하여, 요소의 찌그러짐(distortion)에 관계없이 신뢰성 있는 결과를 보여주었다. 또한 개발된 요소들은 강체운동(rigid body motion)에 필요한 최소의 zero eigenvalue를 가지며, 두꺼운 평판은 물론 아주 얇은 평판의 해석에서도 항상 좋은 결과를 보여주었다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 춘계학술대회
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• pp.871-874
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• 2010

세계적으로 에너지원의 고갈, 기후 환경 변화, 전력수요 증가에 따라 인류 절대적 과제에 대한 결책으로 스마트 그리드에 대한 요구가 증대되고 있으며, 특히 분산형 전원에 대한 관심이 높아지고 있다. 이 추세에 다라 단위 규모의 분산형 전원의 형태로 댁내 분산형 전원 시대를 예고하고 있다. 하지만 현재 가장 보편적으로 사용하고 있는 신재생에너지원으로써 풍력, 태양광 에너지 발전의 경우 그 발전량이 자연의 변화에 매우 민감하기 때문에 전기품질의 균일성의 문제를 가지고 있다. 따라서 본 논문에서는 이를 해결하기 위해서는 기후 정보(meteorological sensor data)의 실시간 모니터링을 기반으로 하는 에너지 관리 방법을 제시하고자 한다. 현재 스마트그리드 분야에서 USN 기반의 킬러앱이 부재한 상황에서 무선 센서네트워크 기술을 활용한 기후 센서 데이터 수집 및 제어 방식을 적용한 댁내 분산 전력 관리 방법에 대해 제안한다. 이는 다른 통신방식에 비해 설치 비용 및 유지보수 차원에서 효율적이라고 판단한다. 즉, 전력 관리에 USN 기법을 융합한 EMS(Energy Management System) 모델을 제시함으로써 기후 데이터 모니터링 및 분석, 이에 따른 발전량 예측, 신재생에너지와 기존 전력의 효율적인 분배 제어 방법을 구체화함으로써 궁극적으로 제로에너지 홈을 구현하기 위한 기반을 마련하는 것이 본 논문의 목표이다.

• 천문학회보
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• 제38권2호
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• pp.60.2-60.2
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• 2013

Electron magnetohydrodynamic (EMHD) turbulence provides a fluid-like description of small-scale magnetized plasmas. Most EMHD turbulence studies consider "balanced" EMHD turbulence. However, imbalanced EMHD turbulence has never been studied. In this study, we numerically study "imbalanced" EMHD turbulence. Imbalanced turbulence means that wave packets moving in one direction have high amplitudes or strong perturbations than the others. In driven imbalanced EMHD turbulence, non-zero magnetic helicity is injected. When magnetic helicity is injected at a scale, we expect to have inverse cascade of magnetic helicity, as well as magnetic energy, in three-dimensional (3D) EMHD turbulence. For no helicity injection, we do not observe inverse energy cascade. However, when magnetic helicity is injected, inverse cascade of magnetic helicity is clearly observed. Magnetic energy also shows inverse cascade. In EMHD turbulence, it is well known that magnetic energy on scales smaller than the energy injection scale is forward-cascading quantity and the magnetic energy spectrum follows a k^{-7/3} one. On the other hand, the inverse-cascading entity on scales larger than the energy injection scale is uncertain. If the magnetic helicity is inverse-cascading quantity, we will obtain a k^{-5/3} magnetic energy spectrum. In our simulations, we do observe energy spectrum consistant with k^{-5/3} on large scales. Therefore, we confirm that magnetic helicity indeed is the inverse-cascading entity in 3D EMHD turbulence.

• Asian Journal of Innovation and Policy
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• 제5권2호
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• pp.208-224
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• 2016

The Korean government considers expanding the WtE share of total energy from 1% to 5% by 2020 through research and development (R&D) in waste-to-energy (WtE) technologies. This study attempts to measure the external benefits of investing in R&D in these technologies. To this end, a contingent valuation (CV) is employed. More specifically, a 2016 national survey of randomly selected 1,000 households was carried out across the nation to gauge the willingness to pay (WTP) for the investment. One-and-one-half-bounded dichotomous choice question was used in the CV survey, and the spike model was applied to dealing with zero WTP responses. The mean yearly WTP is estimated to be KRW 4,175 (USD 3.57) per household, which is statistically significant at the 1% level. Expanding the value to the entire nation translates into an investment of about KRW 79.1 billion (USD 67.6 million), which can be interpreted as the annual external benefit of the R&D investment in WtE technology.

• 신재생에너지
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• 제19권1호
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• pp.22-30
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• 2023

Recently, the use of renewable energy has been increasing to achieve carbon neutrality. The concept of a zero-energy building is also attracting attention. In this study, a preliminary study was conducted to analyze the feasibility of a hybrid wind and solar power generation system between buildings that utilize the building wind generated by the Venturi effect. For this purpose, the wind speed and sunshine hours were monitored in the area where the building wind blows by the Venturi effect, and the power generation depending on system types, areas, and season was estimated. Consequently, the wind power generation system showed a larger amount of power per area than solar power. The wind power systems can generate larger power if wind power blades are installed along the height of the building. As a preliminary study, this study verified the feasibility of the system utilizing building wind and suggested follow-up studies.

• Advances in nano research
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• 제13권5호
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• pp.475-485
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• 2022

Crystalline silicon photovoltaic cells have advantages of zero pollution, large scale and high reliability. A major challenge is that sunlight wavelength with photon energy lower than semiconductor band gap is converted into heat and increase its temperature and reduce its conversion efficiency. Traditional cooling PV method is using water flowing below the modules to cool down PV temperature. In this paper, the idea is proposed to reduce the temperature of the module and improve the energy conversion efficiency of the module through the modulation of the solar spectrum. A spectrally selective nanofilm reflector located directly on the surface of PV is designed, which can reflect sunlight wavelength with low photon energy, and even enhance absorption of sunlight wavelength with high photon energy. The results indicate that nanofilm reflector can reduce spectral reflectivity integral from 9.0% to 6.93% in 400~1100 nm wavelength range, and improve spectral reflectivity integral from 23.1% to 78.34% in long wavelength range. The nanofilm reflector can reduce temperature of PV by 4.51℃ and relatively improved energy conversion efficiency of PV by 1.25% when solar irradiance is 1000 W/m². Furthermore, the nanofilm reflector is insensitive in sunlight's angle and polarization state, and be suitable for high irradiance environment.