• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.7
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• pp.984-991
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• 2015

This paper presents the methodology for optimal design of power grid for offshore wind power plant (OWPP) and optimum location of offshore substation. The proposed optimization process is based on a genetic algorithm, where the objective cost model is composed of investment, power loss, repair, and reliability cost using the net present value during the whole OWPP life cycle. A probability wind power output is modeled to reflect the characteristics of a wind power plant that produces electricity through wind and to calculate the reliability cost called expected energy not supplied. The main objective is to find the minimum cost for grid connection topology by submarine cables which cannot cross each other. Cable crossing was set as a constraint in the optimization algorithm of grid topology of the wind power plant. On the basis of this method, a case study is conducted to validate the model by simulating a 100-MW OWF.

• Journal of the Korean Chemical Society
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• v.53 no.6
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• pp.653-662
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• 2009

Developing effective tools for predicting absorption, distribution, metabolism, excretion properties and toxicity (ADME/T) of new chemical entities in the early stage of drug design is one of the most important tasks in drug discovery and development today. As one of these attempts, support vector machines (SVM) has recently been exploited for the prediction of ADME/T related properties. However, two problems in SVM modeling, i.e. feature selection and parameters setting, are still far from solved. The two problems have been shown to be crucial to the efficiency and accuracy of SVM classification. In particular, the feature selection and optimal SVM parameters setting influence each other, which indicates that they should be dealt with simultaneously. In this account, we present an integrated practical solution, in which genetic-based algorithm (GA) is used for feature selection and grid search (GS) method for parameters optimization. hERG ion-channel inhibitor classification models of ADME/T related properties has been built for assessing and testing the proposed GA-GS-SVM. We generated 6 different models that are 3 different single models and 3 different ensemble models using training set - 1891 compounds and validated with external test set - 175 compounds. We compared single model with ensemble model to solve data imbalance problems. It was able to improve accuracy of prediction to use ensemble model.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.150-151
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• 2012

The utility grid has a supply of electric energy which is larger than the usually required power consumption under peak load condition. So, power distribution is required to have a heavy capacity because of peak-load period. To solve the problem, this paper proposes a 10kW rapid charger system which has a function of load compensation at the peak-load condition. The proposed system supplies power demanded by peak-load through transferring energy in the battery of electric vehicle to the grid. V2G operation is verified through simulation performed by 10kW rapid-charger.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.90-95
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• 1998

The two-dimensional incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. Incompressible code using pseudo-compressibility and dual-time stepping method involves a conventional upwind differencing scheme for the convective terms and LU-SGS scheme for time integration. Compressible code also adopts an FDS scheme and LU-SGS scheme. Several two-equation turbulence models (the standard $k-{\varepsilon}$ model, the $k-{\omega}$ model. and $k-{\omega}$ SST model) are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by computing the flow around the transonic RAE2822 airfoil and the NACA4412 airfoil, respectively. Both the results show a good agreement with experimental surface pressure coefficients and velocity profiles in the boundary layers. Also, the GA(W)-1 single airfoil and the NLR7301 airfoil with a flap are computed using the two-equation turbulence models. The grid systems around two- and three-element airfoil are efficiently generated using Chimera grid scheme, one of the overlapping grid generation methods.

• Advances in Energy Research
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• v.4 no.2
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• pp.163-176
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• 2016

Rapid depletion of fossil based oil, coal and gas reserves and its greater demand day by day necessitates the search for other alternatives. Severe environmental impacts caused by the fossil fire based power plants and the escalating fuel costs are the major challenges faced by the electricity supply industry. Integration of Distributed Generators (DG) especially, wind and solar systems to the grid has been steadily increasing due to the concern of clean environment. This paper focuses on a new simple and fast load flow algorithm named Backward Forward Sweep Algorithm (BFSA) for finding the voltage profile and power losses with the integration of various sizes of DG at different locations. Genetic Algorithm (GA) based BFSA is adopted in finding the optimal location and sizing of DG to attain an improved voltage profile and considerable reduced power loss. Simulation results show that the proposed algorithm is more efficient in finding the optimal location and sizing of DG in 15-bus radial distribution system (RDS).The authenticity of the placement of optimized DG is assured with other DG placement techniques.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.319-319
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• 2010

칼코젠계 태양전지의 광흡수층으로 사용되는 CuInSe2은 직접천이형 반도체로 광흡수계수가 $1{\times}105cm-1$로 매우 높고, 전기광학적 안정성이 우수하여 실리콘 결정질 태양전지를 대체할 고효율 태양전지로 각광받고 있다. 광흡수층의 밴드갭 에너지가 증가하면 태양전지의 개방전압(Voc)이 증가하여 광변환 효율을 향상시킬 수 있으므로, CuInSe2에서 In의 일부를 Ga으로 치환하여 에너지 밴드갭의 변화를 주는 연구가 많이 진행되고 있다. 그러나 화합물내의 Ga 조성비가 증가하면 단락전류(Jsc), 충진률(fill factor)이 낮아져 태양전지 효율을 저하시키게 되므로 CIGS 박막의 적절한 화합물 조성비를 갖도록 최적조건을 확립하는 것이 매우 중요하다. 본 실험에서는 광흡수층 형성을 위해 Sputtering법으로 금속 전구체를 증착하고, 고온에서 셀렌화 열처리를 수행하는 Sequential process(2단계 증착법)를 이용하였다. soda-lime glass 기판에 Back contact으로 Mo를 증착하고, 1단계로 CuIn0.7Ga0.3 조성비의 타겟을 이용하여 Sputtering법으로 $0.5{\sim}2{\mu}m$ 두께의 CIG 전구체를 증착하였다. 2단계로 CIG 전구체의 셀렌화열처리를 통하여 CIGS 화합물 구조의 박막을 형성시켰다. 이때 형성된 CIGS 화합물 박막의 두께는 동일하게 함으로써, 열처리온도에 의한 박막의 구조변화를 비교하였다. 증착된 CIGS 박막은 고온 엑스선회절분석을 통해 증착 두께와 온도 변화에 따른 CIGS 층의 구조 변화를 확인하고, 동일한 증착조건으로 Buffer layer, Window layer, Grid 전극을 형성하여 태양전지셀 특성을 평가함으로써 CIGS 태양전지 광흡수층의 결정구조에 따른 광변환 효율을 비교하였다.

• Journal of Power Electronics
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• v.15 no.4
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• pp.1119-1130
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• 2015

This study investigates the multi-objective fuzzy optimization of crowbar resistance for the doubly fed induction generator (DFIG) low-voltage ride-through (LVRT). By integrating the crowbar resistance of the crowbar circuit as a decision variable, a multi-objective model for crowbar resistance value optimization has been established to minimize rotor overcurrent and to simultaneously reduce the DFIG reactive power absorbed from the grid during the process of LVRT. A multi-objective genetic algorithm (MOGA) is applied to solve this optimization problem. In the proposed GA, the value of the crowbar resistance is represented by floating-point numbers in the GA population. The MOGA emphasizes the non-dominated solutions and simultaneously maintains diversity in the non-dominated solutions. A fuzzy-set-theory-based is employed to obtain the best solution. The proposed approach has been evaluated on a 3 MW DFIG LVRT. Simulation results show the effectiveness of the proposed approach for solving the crowbar resistance multi-objective optimization problem in the DFIG LVRT.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.36.1-36.1
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• 2010

While the substrate-type solar cells with Cu(In,Ga)Se2 absorbers yield conversion efficiencies of up 20%[1], the highest published efficiency of Cu(In,Ga)Se2 superstrate solar cell is only 12.8% [2]. The commerciallized Cu(In,Ga)Se2 solar cells are made in the substrate configuration having the stacking sequence of substrate (soda lime glass)/back contact (molybdenum)/absorber layer (Cu(In,Ga)Se2)/buffer layer (cadmium sulfide)/window layer (transparent conductive oxide)/anti reflection layer (MgF2) /grid contact. Thus, it is not possible to illuminate the substrate-type cell through the glass substrate. Rather, it is necessary to illuminate from the opposite side which requires an elaborate transparent encapsulation. In contrast to that, the configuration of superstrate solar cell allows the illumination through the glass substrate. This saves the expensive transparent encapsulation. Usually, the high quality Cu(In,Ga)Se2 absorber requires a high deposition temperature over 550C. Therefore, the front contact should be thermally stable in the temperature range to realize a successful superstrate-type solar cell. In this study, it was tried to make a decent superstrate-type solar cell with the thermally stable ZnO:Al layer obtained by adjusting its deposition parameters in magnetron sputtering process. The effect of deposition condition of the layer on the cell performance will be discussed together with hall measurement results and current-voltage characteristics of the cells.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1356-1358
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• 2003

This paper describes the control of grid connected transformerless type PV power conditioning system, which is simple and more efficient than the usual transformer type system. With the modeling and analysis of power system, the validity of control strategy is well verified through the simulation and experimental results.

• Journal of the Korean Institute of Gas
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• v.22 no.5
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• pp.124-132
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• 2018

The supply of renewable energy has become more vigorous due to Paris Agreement. In Korea, supply policies of renewable energy is being promoted with priority given to public buildings, so, the supply of fuel cell system that are relatively easy to install in buildings is expected to expand, so it is important that study on anti-islanding evaluation of grid-connected power conditioning system(PCS) for fuel cell. In this study, we consider that KGS AB934 PC53 in domestic certification standard of PCS for fuel cell correspond with abroad standard and analyze anti-islanding evaluation that important safety performance when connected grid. Additionally, we constructed a prototype for anti-islanding evaluation of PCS for fuel cell connected in parallel and carried out the demonstration evaluation, so, we have conducted ways that ensure safety performance in accordance with the circumstances where several fuel cell systems are installed.