Li-ion 배터리 충/방전 시스템의 안정적 운영에 관한 연구

여성대,조태일,이경량,김성권,한철규 한국전자통신학회 2016 한국전자통신학회 논문지 Vol.11 No.4

When the operation of battery is converted at charging and discharging system based on a DC micro grid, the voltage is fluctuated. And excessive voltage fluctuation could cause damage or failure of charging and discharging equipment. Therefore, in this paper, we studied the operating schedule of the charging and discharging system based on the DC micro grid and a design point of the capacitor which was able to reduce the voltage fluctuation. A result of computer simulation showed that when a fluctuation-reducing capacitor which had an initial value of 600V/35mF was applied at the charging and discharging system based on a DC micro grid which was operated with three charging battery sets and five discharging battery sets, voltage fluctuation by charging and discharging operation was reduced by about 63.3%. Furthermore, voltage fluctuation which occurred when initial network voltage was stabilized was reduced by about 73%. DC μ-Grid 기반의 충/방전 시스템에서 배터리의 동작 변환 시, 망 전압의 fluctuation이 발생하게 되며, 과다한 fluctuation은 충/방전 시스템의 손상 및 고장을 일으킬 수 있다. 따라서 본 논문에서는 DC μ-Grid 기반의 충/방전 시스템에서 fluctuation 완화용 커패시터의 적용 및 설계 포인트에 대하여 연구하였다. 컴퓨터 시뮬레이션 결과, 3개의 충전 배터리 set와 5개의 방전 배터리 set의 조건으로 운영되는 DC μ-Grid 기반 충/방전 시스템에서 600V/35mF의 초기 값을 갖는 fluctuation 완화용 커패시터를 적용하였을 때 충/방전에 의한 fluctuation을 약 66.3% 감소시킬 수 있었으며, 추가적으로 초기 망 전압 안정화 시 발생하는 fluctuation 또한 약 73% 감소시킬 수 있었다.

Ga Content and Thickness Inhomogeneity Effects on Cu(In, Ga)Se2 Solar Modules

Xiaobo Zhu,Tzu-Huan Cheng,Chee-Wee Liu 대한금속·재료학회 2016 ELECTRONIC MATERIALS LETTERS Vol.12 No.4

The fluctuation of Ga content and absorption layer thickness of Cu(In,Ga)Se2 (CIGS) solar modules is investigated by 3-dimensional numericalsimulation. The band gap of CIGS is increased by the increasing Gacontent, and the residual compressive strain. Strain effect worsens thedegradation of the power conversion efficiency of CIGS module in additionto Ga fluctuation. The intracell Ga fluctuation degrades the open circuitvoltage due to the minimum open circuit voltage in the parallelconfiguration, and also affects the short circuit current due to the Gadependentlight absorption. The intercell Ga fluctuation leads to a moresignificant degradation for CIGS solar module efficiency than the intracellGa fluctuation due to the additional degradation of the fill factor. Thethickness fluctuation has a small effect on open circuit voltage, but causesstrong degradation of short circuit current and fill factor, which leads to amore significant degradation on power conversion efficiency than Gafluctuation to the same fluctuation percentage. In reality, the thickness canbe tightly controlled within the fluctuation of 5% or less.

국가계약법령상 물가변동에 따른 계약금액 조정 규정의 적용을 배제하는 합의의 효력

이영선 사법발전재단 2018 사법 Vol.1 No.43

구 국가를 당사자로 하는 계약에 관한 법률 제19조는 “각 중앙관서의 장 또는 계약담당공무원은 공사·제조·용역 기타 국고의 부담이 되는 계약을 체결한 다음 물가의 변동, 설계변경 기타 계약내용의 변경으로 인하여 계약금액을 조정할 필요가 있을 때에는 대통령령이 정하는 바에 의하여 그 계약금액을 조정한다.”라고 규정하였다. 그런데 국가 등과 계약상대자가 물가변동의 경우에도 계약금액을 조정하지 않기로 약정을 체결한 경우 그 합의가 유효한지 여부가 다투어졌다. 이에 대하여 대상판결의 다수의견은 국가계약법상 물가의 변동으로 인한 계약금액 조정 규정은 계약상대자가 계약 당시에 예측하지 못한 물가의 변동으로 계약이행을 포기하거나 그 내용에 따른 의무를 제대로 이행하지 못하여 공공계약의 목적 달성에 지장이 초래되는 것을 막고, 세금을 재원으로 하는 공공계약의 특성상 계약체결 후 일정 기간이 지난 시점에서 계약금액을 구성하는 각종 품목 또는 비목의 가격이 급격하게 상승하거나 하락한 경우 계약담당자 등으로 하여금 계약금액을 조정하는 내용을 공공계약에 반영하게 함으로써 예산 낭비를 방지하고 계약상대자에게 부당하게 이익이나 불이익을 주지 않으려는 뜻도 있으므로, 계약담당자 등은 개별 계약의 구체적 특성, 계약이행에 필요한 물품의 가격 추이 및 수급 상황, 환율변동의 위험성, 정책적 필요성, 경제적 변동에 따른 위험의 합리적 분배 등을 고려하여 계약상대자와 물가변동에 따른 계약금액 조정 조항의 적용을 배제하는 합의를 할 수 있다고 판단하였다. 반면 대상판결의 반대의견은 국가계약법 제19조가 강행규정이고, 이를 배제하는 약정은 효력이 없다고 보았다. 한편 계약상대자가 물가변동에 따른 계약금액 조정조항의 적용을 배제하는 특약을 어쩔 수 없이 수용하게 되는 등 부당하게 불이익을 입게 되는 경우 국가를 당사자로 하는 계약에 관한 법률 시행령 제4조에 의하여 그 특약은 효력이 없다. 여기서 어떠한 특약이 계약상대자의 계약상 이익을 부당하게 제한하는 것으로서 국가계약법 시행령 제4조에 위배되어 효력이 없다고 하기 위해서는 그 특약이 계약상대자에게 다소 불이익하다는 점만으로는 부족하고, 국가 등이 계약상대자의 정당한 이익과 합리적인 기대에 반하여 형평에 어긋나는 특약을 정함으로써 계약상대자에게 부당하게 불이익을 주었다는 점이 인정되어야 한다. 대상판결은 먼저 국가계약법령상 물가변동에 따른 계약금액 조정조항의 성격을 분명하게 선언하였다는 데 의의가 있다. 실무는 위 조항의 성격을 두고 엇갈린 판단을 하였으나, 대상판결로 그러한 혼란은 사라지게 되었다. 나아가 대상판결은 위와 같은 합의가 계약상대자의 이익을 부당하게 제한하는 경우 계약상대자를 보호하기 위한 주된 수단으로 국가계약법 시행령 제4조를 들고, 어떤 경우 위 조항에 위배되어 효력을 부정하게 되는지 판단 기준을 제시하였다. 다만 실제 사안에서 어떤 합의가 계약상대자의 이익을 부당하게 제한하는 경우에 해당하는지에 관하여는 사례의 축적과 학계의 심도 있는 논의가 계속되어야 할 것이다. 주제어: 국가계약법, 공공계약, 물가변동, 계약금액 조정, 내부규정, 강행규정, 계약자유 Article 19 of the former Act on Contracts to Which the State Is a Party (hereinafter “State Contracts Act”) provides, “If it is necessary to adjust the contract amount due to price fluctuation, design modifications, or any other modifications to the content of the contract after the conclusion of a contract for construction work, manufacture, service, etc. which imposes a burden on the national treasury, the head of each central government agency or a public official in charge of contracts shall adjust the contract amount pursuant to the provisions of the Presidential Decree.” Against this backdrop, at issue in the subject case was whether certain terms and conditions were effective when they were entered into between the State and its counterparty, agreeing not to adjust the contract amount notwithstanding price fluctuation. The Majority Opinion held as follows: (a) the provision on the adjustment of contract amount due to price fluctuation under the State Contracts Act is intended to prevent a situation where a counterparty renounces contractual performance or fails to duly perform its contractual obligation due to price fluctuation unanticipated at the time of conclusion of the contract, thereby undermining the attainment of the purpose of a public contract; (b) given the nature of a public contract funded by taxpayers’ money, the provision is also intended to prevent any waste of government budget, without unfairly putting the counterparty either at an advantage or a disadvantage, by having the contracting officer reflect on a public contract the adjustment of contract amount in the event that the price of each item of goods or item constituting the contract amount sharply rises or drops at a certain point after the contract conclusion; (c) a contract officer, etc. may enter into an agreement with the counterparty to exclude the application of the provision on the adjustment of contract amount due to price fluctuation, taking into account such factors as specific features of the individual contract, trends in price and supply of the goods necessary for contract performance, risks of currency fluctuation, policy needs, and reasonable allocation of risks according to economic fluctuation. In contrast, the Dissenting Opinion held that Article 19 of the State Contracts Act is a mandatory provision, and any agreement excluding its application is void. Meanwhile, Article 4 of the Enforcement Decree of the Act on Contracts to Which the State Is a Party (hereinafter “State Contracts Act Enforcement Decree”) renders any special terms and conditions void if they unfairly restrict the counterparty’s contractual interest, such as where the counterparty is forced to accept the special terms and conditions excluding the application of the provision on the adjustment of contract amount due to price fluctuation. Here, to deem certain special terms and conditions void as against Article 4 of the State Contracts Act Enforcement Decree for unfairly restricting the contractual interest of the counterparty, it is not enough for the terms and conditions to be somewhat to the detriment of the counterparty. Rather, the State, etc. must be found to have unfairly disadvantaged the counterparty by setting certain terms and conditions contrary to equity in violation of the counterparty’s legitimate interest and reasonable expectation. The significance of the subject case is that it clarified the nature of the provision on the adjustment of contract amount due to price fluctuation under the State Contracts Act. Thus far, practitioners have had different ideas about the nature of said provision, but the subject case defused the confusion. Moreover, the subject case cited Article 4 of the State Contracts Act Enforcement Decree as a major basis on which to protect the counterparty from any unfair restriction of its interest by certain terms and conditions, and set forth the standard of determining which cases would be void for v...

Fluctuation of the Electric Field in a Plasma

Hee J. Lee 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.8

The theory of electric field fluctuations in a plasma is reviewed. The fluctuations of an electric field can be assumed to be due to the Cerenkov radiation, which is emitted by single particles that satisfy the Landau wave-particle resonance conditions. This view naturally agrees with the picture that a plasma can be considered to be an aggregate of non-interacting dressed particles. A simple classical derivation of the fluctuation-dissipation theorem is presented to show that the fluctuations of the Cerenkov electric field agree with the fluctuation-dissipation theorem. A quasilinear-like solution of the Liouville equation is shown to derive an electric field fluctuation with the same form as that obtained by using the dressed particle approach. We suggest that the fluctuation can be traced to the causality that gives rise to collisionless dissipation (imaginary part of the dielectric function). Therefore, the fluctuation in a plasma has a philosophical implication in that its existence is fundamentally due to the causal principle that the effect cannot be precedent to the cause, thus defining the direction of time.

A Modeling Study of Local Equivalence Ratio Fluctuation in Imperfectly Premixed Turbulent Flames

Moon, Hee-Jang The Korean Society of Mechanical Engineers 2004 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.18 No.8

The effect of fluctuation of Equivalence Ratio (ER) in a turbulent reactive field has been studied in order to check the global combustion characteristics induced by the local fluctuation. When the flow is premixed on a large scale, closer examination on a small scale reveals that local fluctuations of ER exist in an imperfectly premixed mixture, and that these fluctuations must be considered to correctly estimate the mean reaction rate. The fluctuation effect is analyzed with DNS by considering the joint PDF of reactive scalar and ER, followed by modeling study where an extension of stochastic mixing models accounting for the ER fluctuation is reviewed and tested. It was found that models prediction capability as well as its potential is in favor to this case accounting the local ER fluctuation. However, the effect of local fluctuation did not show any notable changes on the mean global characteristics of combustion when statistical independence between the reactive scalar and ER field is imposed, though it greatly influenced the joint PDF distribution. The importance of taking into account the statistical dependency between ER and combustible at the initial phase is demonstrated by testing the modeled reaction rate.

토석류 방재를 위한 사방댐에서의 충격력 해석

김성덕,전근우,김석우,전계원 위기관리 이론과 실천 2015 Crisisonomy Vol.11 No.9

본 연구에서는 유한차분법을 기초로 하여 공급유량 변화 및 수로경사에 따른 토석류의 충격력 특성에 대해서 분석하였다. 공급유량이 많을수록 토석류의 fluctuation이 빠른 시간에서 발생하며, 그 지속시간도 길고, 크기의 진폭도 훨씬 크게 나타난다. 또한, 토석류의 유속은 fluctuation이 발생하는 지점에서의 크기가 토석류 발생 초기 보다 빠르게 수 초간 지속되는 것을 보여준다. 토석류의 충격력은 발생 초기의 첨두(Peak) 값보다 fluctuation이 발생되는 지점에서의 첨두(Peak) 값이 더 크게 되며, 이는 토석류의 에너지 공급원인 공급 유량과 유하하는 토석 류의 입자와의 충돌로 인해 에너지가 상승하게 되고, 크기가 커진 토석류의 충격력이 지속적으로 사방댐에 충격 을 가함으로써 사방댐 안전에 위협이 되고 있음을 나타낸다. This study is to analyze the characteristics of impact force by debris flow based on the Finite Difference Method (FDM), according to the variance of supplying water discharge and channel slope angle. The more supplying water discharges, the earlier fluctuation of debris flow is occurred with a longer duration and a higher amplitude of impact force. The debris flow velocity is speedier at the fluctuation points than on the downstream channel and maintains for a few seconds. The impact force of debris flow at the fluctuation points is stronger than at the early occurrence points. This finding indicates that the supplying water discharge, which is the energy source for debris flow, interacts with the particles of the flowing debris flow and thus the energy of debris flow increases. Such rising impact force of debris flow contains great energy and keeps attacking the check dam.

고속 CMOS A/D 변환기를 위한 기준전압 흔들림 감쇄 회로

박상규,황상훈,송민규,Park Sang-Kyu,Hwang Sang-Hoon,Song Min-Kyu 대한전자공학회 2006 電子工學會論文誌-SD (Semiconductor and devices) Vol.43 No.6

In high speed flash type or pipelining type A/D Converter, the faster sampling frequency is, the more the effect of DC reference fluctuation is increased by clock feed-through and kick-back. When we measure A/D Converter, further, external noise increases reference voltage fluctuation. Thus reference fluctuation reduction circuit must be needed in high speed A/D converter. Conventional circuit simply uses capacitor but layout area is large and it's not efficient. In this paper, a reference fluctuation reduction circuit using transmission gate is proposed. In order to verify the proposed technique, we designed and manufactured 6bit 2GSPS CMOS A/D converter. The A/D converter is based on 0.18um 1-poly 5-metal N-well CMOS technology, and it consumes 145mW at 1.8V power supply. It occupies chip area of $977um\times1040um$. Experimental result shows that SNDR is 36.25 dB and INL/DNL ${\pm}0.5LSB$ when sampling frequency is 2GHz. 고속 Flash, Pipelining type의 CMOS A/D 변환기에서 Sampling frequency가 고주파로 올라감에 따라 Clock Feed-through 현상, Kick-back 현상 등의 영향으로 DC Reference voltage 흔들림 현상이 심화되고 있다. 뿐만 아니라 측정 시 외부 Noise가 Reference voltage에 적지 않은 영향을 미친다는 것을 감안 할 때 High speed A/D converter에서 Reference fluctuation 감쇄회로는 반드시 필요하다. 기존의 방식은 단순히 커패시터를 이용했으나 면적이 크고 효과가 좋지 않다는 단점이 있다. 본 논문에서는 Transmission Gate를 이용한 reference fluctuation 감쇄 회로를 제안하고 흔들림 현상이 크게 개선되었음을 정량적 분석 및 측정을 통하여 증명하였다. 제안하는 회로의 측정을 위해 6bit의 해상도를 갖는 2GSPS CMOS A/D 변환기를 설계 및 제작하였다. 제작된 A/D 변환기를 이용하여 Reference 전압이 40mV의 흔들림이 있음에도 원하는 범위 내에서 동작함을 측정하였다. 본 연구에서는 1.8V $0.18{\mu}m$ 1-poly 5-metal N-well CMOS 공정을 사용하였고, 소비전력은 145mW로 Full Flash 변환기에 비해 낮았다. 실제 제작된 칩의 SNDR은 약 36.25dB로 측정되었고, INL과 DNL은 각각 ${\pm}0.5$ LSB 이하로 나타났다. 유효칩 면적은 $997um\times1040um$ 이었다.

1/f 수준 별 음악 자극이 감정 노동 종사자의 심장 반응에 미치는 효과

전병무 ( Byung Mu Jeon ),황민철 ( Min Cheol Whang ) 한국감성과학회 2015 감성과학 Vol.18 No.3

본 연구는 1/f fluctuation의 α기울기 따라 구성된 사운드를 들었을 때 감정 스트레스 업무에 종사하고 있는 피험자들의 심박 변화를 확인하고자 하였다. 기존의 연구에서는 주로 사용자의 심리상태 안정시키는 효과 또는 생리적 안정성에 1/f fluctuation의 α기울기가 관계가 있는 것으로 보고되었다. 본 연구에서는 1/f fluctuation 수준을 총 3가지나누어 제작한 사운드를 독립변수로 사용하였다. 독립변수는 감정노동 종사자에게 제시하여 그에 따른 심장반응을 측정하였다. 종속변수는 네 가지로 BPM(Beat Per Minute), VLF(Very Low Frequency), SDNN(Standard Deviation of NN intervals), 그리고 HF(High Frequency) 파워(Power)값을 확인하였다. 분석결과 기울기가 3인 1/fluctuation 사운드는 각성효과를 보였다. 기울기 1, 2인 사운드는 이완효과가 있는 것을 통계적으로 검증하였다. 이러한 1/f fluctuation 사운드의 특성을 활용해 감정 노동자들의 스트레스를 완화시키기 위한 서비스에 응용될 수 있을 것으로 사료된다. This study identified heart response of participants while listening to sounds which have 1/f fluctuations with exponent α gradient. The participants were engaged in emotional stress work. Prior studies related to 1/f fluctuation sound have reported that sound source can alleviate psychological and physiological state of users. Subjects of this study were exposed to sound with three levels of α gradient. Heart response of subjects were measured with Photoplethysmography(PPG) sensor simultaneously. The dependent variables of this study were beat per minute(BPM), very low frequency percent of pulse rate variability (VLF percent), the standard deviation of all normal RR intervals (SDNN), and high frequency power(HF power). Subject showed arousal response when exposed to sound with exponent α gradient of 3 whereas the sound with exponent α gradient of 1 and 2 resulted in relax effect. The characteristic of 1/f fluctuation sounds can be applied to alleviate stress for employers under emotional labor.

항공운송에서 화물, 운송인, 화주의 특성이 운임 변동성에 미치는 영향 분석

김두희 ( Kim Doo-hee ),조혁수 ( Cho Hyuk-soo ) 한국해운물류학회(구 한국해운학회) 2020 해운물류연구 Vol.36 No.2

원자재를 수입하고 이를 가공해서 수출하는 우리나라의 무역구조 때문에 경쟁력있는 운임에 기초한 무역운송은 우리나라 경제에서 아주 중요하다. 반도체, IT 제품등이 우리나라 주력 수출품으로 자리 잡으면서 항공운송의 중요성이 높아지고 있다. 본 연구는 항공운송을 중심으로 운임 변동성에 영향을 미치는 요인을 화물, 운임, 화주의 특성으로 분류하여 실증 분석하였다. 또한 운임 변동성이 운송서비스에 대한 화주의 만족도에 어떠한 영향을 미치는지도 확인하였다. 실증분석 결과에 의하면 부대요금의 비중, 계약에 대한 이해수준, 화주의 업력이 운임 변동성에 영향을 미치는 중요한 변수로 확인되었다. 또한 운임 변동성이 작을수록 화주의 운송서비스 만족도도 향상될 수 있었다. 이와 함께, 운임 변동성 관련 포괄적인 변수에 대한 이론적, 실증적 분석이 향후 연구과제의 중요한 주제로 제시되고 있다. Due to the economic structure importing raw materials and exporting products, transportation with competitive freight can play an important role in Korean trade. Incheon Airport is much bigger regarding number and price of international trade in Korea. The competitiveness of air transport depends on various factors. One of them is air freight. This study aims at researching air transport and freight. In specific, this study is designed to find determinants of freight fluctuation in air cargo. Air freight can be fluctuated depending on various factors such as cargo, consignee, carrier, and etc. Also, freight fluctuation can be relevant to service performance in air transport. This study tries to show important determinants and effect of freight fluctuation based on previous research and empirical findings. It is found that surcharge ratio, how much understand contract terms, and how long do business can be relevant to decrease freight fluctuation. Also, lower freight fluctuation better service satisfaction in air transport. Despite its contributions, there are some limitations. We could not find all possible determinants of freight fluctuation. It is required for future research so as to find comprehensive determinants and effects.

Investigation on characteristics of pressure fluctuation in a centrifugal pump with clearance flow

Lulu Zheng,Xiaoping Chen,Wei Zhang,Zu-chao Zhu,Jinglei Qu,Mengmeng Wang,Xiaojie Ma,Xueli Cheng 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.9

Clearance flow has great impact on pressure fluctuation of centrifugal pumps. Numerical calculations are performed to study the pressure fluctuation characteristics of centrifugal pump with wear ring clearance, especially in the regions of interaction between main flow and clearance flow (IMC) and clearance. The accuracy of numerical calculations is illustrated by comparing the experiments of performance and pressure fluctuation. Results show that, in clearance region the pressure fluctuation is still governed by blade passing frequency (f BPF ). Its amplitude of dominate frequency of pressure fluctuation becomes larger as the probe approaches the impeller exit. In IMC region, the pressure fluctuation at impeller outlet is dominated by f BPF . However, the dominate frequency at the entrance of impeller is less than f BPF . In addition, as the flow rate increased, the amplitude of dominate frequency of pressure fluctuation increases at impeller entrance, whereas an inverse trend is observed at wear ring clearance region.