• Journal of Electrical Engineering and Technology
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• 제9권1호
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• pp.1-5
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• 2014

When renewable sources are connected to the distribution network in the form of a distributed generators(DGs), the effect of intermittent output appears as voltage fluctuation. The surplus power at the consumer ends results in the reverse power flow to the distribution network. This reverse power flow causes several problems to the distribution network such as overvoltage. Application of the reactive power control equipment and power flow control by means of BTB inverter have been suggested as the general solutions to overcome the overvoltage, but they are not economically feasible since they require high cost devices. Herein, we suggest the feeder loop line switch control method to solve the problem.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.1175-1176
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• 2006

본 논문은 신재생에너지 발전전원 중 단속적 특성이 강한 풍력발전 전원의 용량가치 평가방법에 관한 것이다. 풍력발전의 설비가치는 확률론적 접근방법과 용량률에 의한 결정론적 접근방법을 사용할 수 있으며 미국의 주요 산정방법을 살펴보고 국내 적용가능한 대안을 수립한다. 풍력발전의 설비가치를 실효성있게 산정하기 위해서는 관련자료의 확보가 우선되어야 하나 국내의 자료확보체계 및 그 기간이 짧은 관계로 용량률에 근거한 단순기법이 실효성이 있을 것으로 판단된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1232-1233
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• 2007

As the number of wind turbines installed increase, the power from wind energy starts to replace conventional generation units and its influence on power system can not be neglected. Because of the intermittent nature of wind resource, the output power of wind turbine fluctuates according to wind speed variation. In this point of view, it is necessary for wind turbines to be equipped with power regulation ability. The doubly fed induction generator (DFIG) is one of the main techniques used in variable speed wind turbines. This thesis focuses on the development of modified control scheme of DFIG to regulate output power. The proposed control scheme achieves active power output regulation so as to stabilize the power system.

• 한국자기학회지
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• 제5권5호
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• pp.695-701
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• 1995

Fundamental issues and general procedures of modeling the head disk interface (HDI) in order to provide design criteria for future ultra-low flying sliders are given. Intermittent contact and gaseous rarefaction effects are discussed using nonconventional kinetic theory. To illustrate the simulation results, we modeled IBM 3370 taper flat sliders and positive/negative "bow tie" sliders. Several alternative HDI concepts for future disk drives - viscoelastic bearings, a hybrid system, and contact recording - are also briefly discussed.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.422-423
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• 2019

In accordance with the Carbon-Free Island by 2030 policy of Jeju Special Self-Governing Province, renewable energy sources are increasing in Jejudo Island. Due to the intermittent output characteristics of wind turbines, one of the renewable energy sources, which can cause unbalanced system conditions between the demand load and the power generation of Jejudo Island. The Korea Power Exchange limits the output of wind turbines for stabilizing the Jeju power system. Therefore, this paper proposes a method to supply a limited output of Sangmyeong Wind Farm in Jeju Power system to Energy Storage System(ESS) and Water Electrolysis Device(WED). The voltage and frequency fluctuation of the Jeju power system is checked accordingly. The simulation results are performed using the PSCAD/EMTDC program.

• 전기전자학회논문지
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• 제26권3호
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• pp.355-363
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• 2022

우리나라는 2050년 탄소중립을 목표로 신재생에너지 중심으로 에너지 공급원을 전환하고 확대하는 계획을 추진 중이다. 신재생에너지의 간헐적 특성으로 에너지 공급이 불안정성이 커짐에 따라 정확한 신재생에너지 발전량 예측의 중요성이 함께 커지고 있다. 이에 따라 정부는 신재생에너지를 집합화하여 관리하기 위한 소규모 전력중개시장을 개설하였고, 재생에너지 발전량 예측제도를 도입하여 예측정확도에 따라 정산금을 지급하는 제도를 시행 중이다. 본 논문에서는 우리나라 신재생에너지 전원의 대부분을 차지하는 태양광 발전에 대하여 통계적 및 인공지능 모형을 이용하여 예측모델을 구현하였으며, 각 모형의 예측정확도 결과를 비교 분석하였다. 비교 모델 중에서 CNN-LSTM(Convolutional Long Short-Term Memory Neural Networks) 모형이 가장 높은 성능을 가짐을 확인하였다. 예측정확도에 따른 예측제도 정산금 수익을 추정해보았고, 예측보유 기술 수준에 따라 수익 편차가 24% 정도 커질 수 있음을 확인하였다.

• 한국지능시스템학회논문지
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• 제25권3호
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• pp.299-305
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• 2015

Global environmental concerns and the ever increasing need of energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Distributed electricity generation is a suitable option for sustainable development thanks to the load management benefits and the opportunity to provide electricity to remote areas. Solar energy being easy to harness, non-polluting and never ending is one of the best renewable energy sources for electricity generation in present and future time. Due to the random and intermittent nature of solar source, PV plants require the adoption of an energy storage and management system to compensate fluctuations and to meet the energy demand during night hours. This paper presents an efficient, economic and technical model for the design of a MPPT based grid connected PV with battery storage and management system. This system satisfies the energy demand through the PV based battery energy storage system. The aim is to present PV-BES system design and management strategy to maximize the system performance and economic profitability. PV-BES (photovoltaic based battery energy storage) system is operated in different modes to verify the system feasibility. In case of excess energy (mode 1), Li-ion batteries are charged using CC-CV mechanism effectively controlled by fuzzy logic based PID control system whereas during the time of insufficient power from PV system (mode 2), batteries are used as backup to compensate the power shortage at load and likewise other modes for different scenarios. This operational mode change in PV-BES system is implemented by State flow chart technique based on SOC, DC bus voltages and solar Irradiance. Performance of the proposed PV-BES system is verified by some simulations study. Simulation results showed that proposed system can overcome the disturbance of external environmental changes, and controls the energy flow in efficient and economical way.

• 한국정보시스템학회지:정보시스템연구
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• 제27권2호
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• pp.95-114
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• 2018

Purpose The recent concern over environmental problems such as greenhouse gas emission and fine dust contributes increasing interest in renewable energies. However the intrinsic characteristics of renewable energies, intermittent and stochastic generation, might cause serious problems to the stability and controllability of power grid. Therefore countermeasures such as virtual power plant (VPP) must be prepared in advance of the spread of uncontrollable distributed renewable energy resources to be one of major energy sources. Design/methodology/approach This study deals with the design concept of the VPP platform. we proposed as a technology solution for achieving the stability of power grid by guaranteeing a single power profile combining multiple distributed power sources with ICT. The core characteristics of VPP should be able to participate in the grid operation by responding to operation instructions from the system operator, KPX, as well as the wholesale electricity market. Findings Therefore this study includes energy storage device(ESS) as a controllable component as well as renewable energy resources such as photovoltaic and wind power generation. Based on this configuration, we discussed core element technologies of VPP and protype design of VPP solution platform according to system requirements. In the proposed solution platform, UX design for the integrated control center and brokerage system were included as well as ancillary service function to respond to KPX's operation instruction with utilizing the capability of ESS. In addition, a simulator was suggested to verify the VPP operations.

• Korean Chemical Engineering Research
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• 제54권4호
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• pp.479-486
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• 2016

순산소 전로 후드의 일산화탄소와 열회수를 위해서는 고효율의 증기를 발생시키는 증기드럼의 장착이 필요하다. 그러나 제선 제강공정에서 증기발생은 간헐적이거나 주기적인 산소 취입공정기간에 제한적이다. 따라서, 증기드럼은 전로의 주기에 따른 산소의 취련기간 동안 효율적으로 증기를 발생시키도록 최적 설계되어야 한다. 따라서 본 연구에서는 다양한 운전조건 및 기하학적 형상변화가 증기드럼 내의 열유동 특성과 성능에 미치는 효과를 예측할 수 있는 3차원 전산유체역학 모델을 제안하였다. 본 모델은 유체유동 및 열전달 뿐만 아니라 계면유동에서의 증발 및 응축을 유한체적법을 사용하여 고려하였다. 본 모델의 예측성능을 검증하기 위하여 실험에서 구한 증기발생량과 비교하였으며 3.2%의 상대오차를 보였다.

• Toxicological Research
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• 제12권1호
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• pp.1-8
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• 1996

The variation in the enzyme activities of human liver usually represents the particular physiological conditions of each individuals. Thus, we investigated the variation in the activities of SOD, HR and LPO of (1) non-exposed workers (56 subjects), and (2) exposed workers to DMF (43 subjects) in synthetic leather process. Serum levels of enzyme activities of exposed workers (AST:$30.26{\pm}20.041$U/L, ALT:$32.72{\pm}23.393$U/L, GGT:$28.47{\pm}18.635$ U/L, ALP:$81.77{\pm}34.879$ U/L)were slightly higher than those in nonexposed workers (AST:$24.00{\pm}9.441$ U/L, ALT:$23.89{\pm}18.305$U/L, GGT:$21.95{\pm}17.970$U/L, ALP:$70.84{\pm}24.678$U/L), but only the level of ALT was statistically significant (p< 0.05). Serum levels of LDH, TRF and CHOL in non-exposed workers were slightly higher than those of exposed workers. However, they were not statistically significant (p > 0.05). Serum levels of HR and LPO of the exposed workers appeared to be reduced, but not those of the non-exposed workers. The SOD activities of exposed workers were also slightly higher than those of non-exposed workers, but the results were not statistically significant (p > 0.05). The level of HR was increased with age, but the SOD level was not. These results suggest that the intermittent exposure to DMF at time-weighted average (TWA) level (10 ppm/$m^3$) has affected on the activities of enzymes such as AST, ALT, TRF, but not on the generation of HR, activity of SOD. However, if high dose of DMF was used, there would be severe effects for the generation of HR and LPO.