• 한국수소및신에너지학회논문집
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• 제35권4호
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• pp.384-391
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• 2024

In this study, a fuel cell with a single stack of 100 cm² was manufactured and a superconducting coil driving experiment was conducted. Fuel cell activation and performance evaluation were performed, and a method of applying current to a superconducting coil using a fuel cell was considered by controlling the flow rate of gas supplied to the fuel cell. A scenario was created using a specific program to change the amount of gas supplied to the fuel cell over time. As a result of analyzing the voltage and magnetic field of the superconducting coil according to the applied current, it was confirmed that the performance of fuel cell was almost the same with that of power supply.

• Journal of Communications and Networks
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• 제7권2호
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• pp.192-206
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• 2005

Integration of mobile networks and Internet has started with 2.5 generation of mobile cellular networks. Internet traffic is today dominant traffic type worldwide. The hanger for higher data rates needed for data traffic and new IP based services is essential in the development of future wireless networks. In such situation, even 3G with up to 2 Mbit/s has not provided data rates that are used by Internet users with fixed broadband dial-up or through wired local area networks. The solution to provide higher bit rates in wireless access network has been found in wireless LAN although initially it has been developed to extend wired LAN into wireless domain. In this paper, we propose and describe a solution created for interoperability between mobile cellular network and WLAN. The integration between two networks, cellular and WLAN, is performed on the authentication, authorization, and accounting, i.e., AAA side. For that purpose we developed WLAN access controller and WLAN AAA gateway, which provide gateway-type access control as well as charging and billing functionalities for the WLAN service. In the development process of these elements, we have considered current development stadium of all needed network entities and protocols. The provided solution provides cost-effective and easy-to-deploy PLMN-WLAN Internetworking scenario.

• 전기학회논문지
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• 제66권7호
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• pp.1007-1016
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• 2017

This paper aims to analyze the safety evaluation of the existing transformer for the 0.85 millions of public rental apartments as EVs(Electric Vehicles) increase in order to overcome the environment pollution issue and maintain sustainable development. It is analyzed that the 56.4% capacity of power transformer could secure as EV charging infrastructure, based on the analysis of respective utilization patterns of the housing and power transformer. The acceptable number of EVs is 0.04~0.06 per household from the spare capacity of the power transformer. It is analyzed that EV stock is prospected less than 0.03 per household in 2030, considering the condition of the public rental apartments residents and the growth rate of EVs according to practical scenario. The power demand for EVs is within the allowable capacity range of the power transformer, so the research shows that there is no problem in the stability of the existing transformer until 2030.

• 신재생에너지
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• 제18권2호
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• pp.50-59
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• 2022

The Korean government announced the "1st Basic Plan for the Transition to Hydrogen Economy" in 2021 and declared the establishment of a hydrogen industry ecosystem by 2040. To build a low-carbon power system, resources that can efficiently accommodate renewable energy are required, and green hydrogen is considered a potential solution. This study analyzed the economic feasibility of green hydrogen-based sector coupling to reduce curtailment of renewable generation in the Jeju power system by 2025 under the scenario of with or without HVDC#3. The result showed that HVDC#3 significantly reduced the frequency of curtailment from 16.1% to 3.0%. In addition, green hydrogen-based sector coupling was an economically feasible option as result showed an IRR of 4.86% when HVDC#3 was connected and 11.45% when it was not under the condition of achieving 50% curtailment reduction. This study shows that the higher the level of renewable energy deployment, the more delayed the HVDC connection between Jeju and the main land, and the lower the SMP, the more economically feasible the green hydrogen-based sector coupling is. Furthermore, this study suggests that the policy goal of completely reducing curtailment is not economically efficient.

• Journal of Electrochemical Science and Technology
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• 제12권4호
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• pp.424-430
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• 2021

The element iron (Fe) is affordable and abundantly available, and thus, it finds use in a wide range of applications. As regards its application in rechargeable lithium-ion batteries (LIBs), the electrochemical reactions of Fe must be clearly understood during battery charging and discharging with the LIB electrolyte. In this study, we conducted systematic electrochemical analyses under various voltage conditions to determine the voltage at which Fe corrosion begins in general lithium salts and organic solvents used in LIBs. During cyclic voltammetry (CV) experiments, we observed a large corrosion current above 4.0 V (vs. Li/Li⁺). When a constant voltage of 3.7 V (vs. Li/Li⁺), was applied, the current did not increase significantly at the beginning, similar to the CV scenario; on the other hand, at a voltage of 3.8 V (vs. Li/Li⁺), the current increased rapidly. The impact of this difference was visually confirmed via scanning electron microscopy and optical microscopy. Our X-ray photoelectron spectroscopy measurements showed that at 3.7 V, a thick organic solid electrolyte interphase (SEI) was formed atop a thin fluoride SEI, which means that at ≥3.8 V, the SEI cannot prevent Fe corrosion. This result confirms that Fe corrosion begins at 3.7 V, beyond which Fe is easily corrodible.

• 융합경영연구
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• 제2권4호
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• pp.1-19
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• 2014

The rule of Islam is simple: if you advance a loan, you are entitled to receive your capital only and nothing more. If you wish to secure profit you should enter into a partnership and become a shareholder. Prohibitions against interest are not peculiar to Islam. If we were to trace back through history, a number of examples of such prohibitions can be found in the early Greek, Roman and Rabinnical thought. With the decline of the influence of the Catholic Church interest transactions become legal and stimulated giant Western corporations which forged capitalist imperialism. The practice of charging interest (usury) now dominated Western law and ethics for over a millennium. But, the Western or capitalist economic system has proven a failure in its quest for economic justice, which serves to benefit all in society, both the rich and the poor. In particular, capitalism is currently causing a terrifying scenario of making the rich richer and the poor poorer due to interest charges. An alternative banking model, called Islamic finance and banking, is evoked in this study in order to depress financial exploitation by banking institutions.

• 한국전자파학회논문지
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• 제24권9호
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• pp.883-891
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• 2013

스마트폰 무선 충전 시나리오에서는 송신 패드에 비해 수신 패드의 크기가 작으므로 수신 패드의 위치에 상관없이 일정한 전력을 부하에 공급하는 것이 중요하다. 본 논문에서는 송신 패드와 수신 패드의 크기가 각각 $16cm{\times}18cm$와 $6cm{\times}8cm$의 직사각형 구조를 갖는 경우, 무선 전력 전송 송신부에 위치한 E급 증폭기의 Drain 바이어스 전압만을 조정하여 수신 패드의 위치에 상관없이 일정한 전력이 부하에 공급되는 방식을 제안하였다. 설계된 LF-대역 무선 전력 시스템의 구성은 PWM IC인 TL494로 제어되는 Buck converter 구조의 전원 회로, 저가의 IRF510 power MOSFET을 이용한 E급 증폭기, 송신 패드 및 수신 패드, 그리고 Schottky 다이오드를 이용한 풀 브릿지 정류기로 구성된다. 제작된 무선 전력 전송 시스템은 바이어스 조정을 하지 않는 경우 240 kHz에서 최대 4 W 출력과 67 % 이상의 시스템 효율을 가지며, 바이어스 조정을 하는 경우에는 수신 패드의 위치에 상관없이 수신 전력을 2 W로 일정하게 유지할 수 있다.

• 한국가스학회지
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• 제25권2호
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• pp.13-21
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• 2021

최근 수소자동차 보급의 확대로 수소충전소의 설치가 점차 확대될 예정이다. 본 연구에서는 수소충전소의 최악의 상황을 가정한 시나리오를 기반으로 피해규모를 예측하고 보다 안전한 설계형태를 제안하고자 한다. 피해규모 예측 방법은 전산유체역학(CFD)을 이용한 Flacs solver를 사용하였으며 이전 연구자의 실험 결과와 비교하여 정확성을 검증하였다. 피해규모 예측은 수소누출과 폭발에 대해서 실시하였으며, 예측 대상은 실측치를 기반으로 한 KR model로 하였다. 그리고 비교검토 모델로는 천정이 없는 형태인 Roofless model을 선정하였다. 두 모델에 대하여 분석한 결과 KR model에서는 내부가 60 vol% 이상까지 수소가스가 누적·체류되는 현상을 확인 할 수 있었던 반면, Roofless model의 경우에는 누출 후 벽면을 타고 충전소 외부로 방출·확산되는 현상을 확인 할 수 있었다. 결론적으로 국내에 표준모델로 보급·확산되고 있는 수소충전소 모델보다는 천정이 없는 수소 충전소 형태가 안전상 유리한 것으로 검토되었다.

• 한국정보통신학회논문지
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• 제16권2호
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• pp.279-287
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• 2012

전기 자동차의 배터리는 휘발유 경유로 연료를 공급하는 자동차에 비해 배터리 충전에 오랜 시간이 소요된다. 이는 전기 자동차의 상용화를 위해 산업계에서 해결해야 할 문제이다. 따라서 관련 업계에서는 배터리 교환소에서 충전되어 있는 배터리를 교체해 주는 방안이 제시되고 있다. 하지만, 아직 배터리 교체 방법에 대한 보안 위협과 요구 사항 등에 대한 연구가 미비한 실정이다. 본 논문에서는 배터리 교체 충전 방식에서 보안을 위협하는 요소들을 살펴보고, 이를 해결하기 위해 보안 요구사항을 적용한 배터리 교체식 시스템을 정의한다. 본 논문의 연구 결과는 추후 배터리 충전 방식의 상용화 및 해당 분야의 보안 분석에 있어 참고자료의 역할을 할 것으로 기대된다.

• 전기학회논문지
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• 제63권11호
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• pp.1615-1621
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• 2014

A wireless tram which runs without catenary and instead uses batteries installed in the tram has been recently researched actively. This paper presents a new method maximizing absorption of regenerative energy of a wireless tram and extending life cycle of the energy storage device in the wireless tram by applying line-optimized charging and discharging scenario. Energy efficiency and life cycle of energy storage system (ESS) are highly dependent on the characteristic of operating conditions. For example, frequent charge and discharge with high power cause the problems that decrease the battery life cycles. Hybrid energy storage system (HESS) is combination of two ESSs which have complementary characteristics to each other. HESS can provide even better functionality and performance than the battery only ESS due to the synergy effect of two ESSs. This paper also provides a power distribution strategy and driving scenarios which increase the life cycle and energy efficiency of the HESS consisting of a battery and an ultra-capacitor. The developed strategy was tested and verified by a hardware-in-the-loop-simulation (HILS) system which emulates the a wireless tram.