• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.2
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• pp.233-238
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• 2018

This paper proposes a seamless MPPT operation mode transfer method of photovoltaic system. The photovoltaic system consists of a DC-DC boost converter, a DC-Link, and a 3-level neutral point clamp (NPC) type inverter. The PV voltage fluctuates due to the output characteristics of the solar pane1 depending on the irradiation amount and the temperature. The photovoltaic system requires seamless MPPT mode transfer method that the discontinuity does not occur in order to supply the stable power to system without affecting the fluctuation of the PV voltage. MPPT operation is divided into two modes by the voltage reference. Under the condition that the PV voltage is below 650V, the DC-DC boost converter performs MPPT through duty control based on perturb & observe (P&O) method, and the inverter conducts DC-link voltage and grid current controls in synchronous reference frame. On the other hand, when the PV voltage exceeds above 650V, inverter performs MPPT in accordance with the variation of DC-link voltage control while the converter stops operating. Two MPPT operation modes is smoothly transferred through the proposed method that DC-link voltage or grid current commands are appropriately adjusted from the certain criteria. The feasibility of the MPPT operation mode transfer method is verified using a 10kW solar photovoltaic system, experimental results have good performances that the fluctuation of PV current is reduced to 100%.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.4
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• pp.235-241
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• 2016

Grid-connected, large-capacity energy storage systems (ESS) can be used for peak load supply, frequency regulation, and renewable energy output smoothing. In order to confirm the capability of battery ESS to provide such services, 4MW/ 8MWh battery ESS demonstration facility was built in the Jocheon substation on Jeju Island. The frequency regulation technology developed for the Jocheon demonstration facility then became the basis for the 28MW and 24MW frequency regulation ESS facilities installed in 2014 at the Seo-Anseong and Shin-Yongin substations, respectively. The operation control systems at these two facilities were continuously improved, and their successful commercialization led to the construction of additional ESS facilities all over Korea in 2015. In seven (7) locations nationwide (e.g., Shin-Gimje and Shin-Gyeryeong), a total of 184 MW of ESS had been commercialized in 2016. The trial run for the new ESS facilities had been completed between April and May in 2016. In this paper, results of the trial run from each of the ESS facilities are presented. The results obtained from the Seo-Anseong and Shin-Yongin substations during a transient event by a nuclear power plant trip are also presented in this paper. The results show that the frequency regulation battery ESS facilities were able to quickly respond to the transient event and trial run of ESS is necessary before it is commercialized.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.21 no.2
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• pp.89-107
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• 2017

In this paper, we have proposed a modified Marker-And-Cell (MAC) method to investigate the problem of an unsteady 2-D incompressible flow with heat and mass transfer at low, moderate, and high Reynolds numbers with no-slip and slip boundary conditions. We have used this method to solve the governing equations along with the boundary conditions and thereby to compute the flow variables, viz. u-velocity, v-velocity, P, T, and C. We have used the staggered grid approach of this method to discretize the governing equations of the problem. A modified MAC algorithm was proposed and used to compute the numerical solutions of the flow variables for Reynolds numbers Re = 10, 500, and 50000 in consonance with low, moderate, and high Reynolds numbers. We have also used appropriate Prandtl (Pr) and Schmidt (Sc) numbers in consistence with relevancy of the physical problem considered. We have executed this modified MAC algorithm with the aid of a computer program developed and run in C compiler. We have also computed numerical solutions of local Nusselt (Nu) and Sherwood (Sh) numbers along the horizontal line through the geometric center at low, moderate, and high Reynolds numbers for fixed Pr = 6.62 and Sc = 340 for two grid systems at time t = 0.0001s. Our numerical solutions for u and v velocities along the vertical and horizontal line through the geometric center of the square cavity for Re = 100 has been compared with benchmark solutions available in the literature and it has been found that they are in good agreement. The present numerical results indicate that, as we move along the horizontal line through the geometric center of the domain, we observed that, the heat and mass transfer decreases up to the geometric center. It, then, increases symmetrically.

• Korean Journal of Adult Nursing
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• v.29 no.3
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• pp.266-277
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• 2017

Purpose: The purpose of this study was to design a mobile-application of a cognitive training program for people who have chemo-related cognitive complaints. Methods: The program was developed based on the network-based instructional system design proposed by Jung. The program consisted of several tasks centered on four cognitive domains: learning, memory, working memory, and attention. For memory learning, a target-image and all its elements (color, position, and number) were presented on the screen that had to be recognized among a number of distractor-figures. In working memory training, the previous learned target-figure according to the level of difficulty had to be remembered among many different figures. In attention training named "Find the same figure," two identical symbols in a grid-pattern filled with different images were presented on the screen, and these had to be simultaneously touched. In attention training named "Find the different figure," a different symbol in a grid pattern filled with same figures had to be selected. This program was developed to train for a minimum of 20 min/day, four days/week for six weeks. Results: This cognitive training revealed statistically significant improvement in subjective cognitive impairments (t=3.88, p=.006) at six weeks in eight cancer survivors. Conclusion: This cognitive training program is expected to offer individualized training opportunities for improving cognitive function and further research is needed to test the effect in various settings.

• Clinical and Experimental Reproductive Medicine
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• v.29 no.4
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• pp.229-236
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• 2002

Objective : The purpose of this study was to evaluate the effect of Cytochalasin B (CCB) on the cytoskeletal stability of mouse oocyte frozen by vitrification. Methods : Mouse oocytes retrieved from cycle stimulated by PMSG and hCG were treated by CCB and then vitrified in EFS-30. These oocytes were placed onto an EM grid and submerged immediately in liquid nitrogen. Thawing of the oocytes was carried out at room temperature for 5 seconds, then the EM grid was placed into 0.75 M, 0.5 M and 0.25 M sucrose at $37^{circ}C$ for 3 minutes, each. These oocytes were fixed in 4% formaldehyde for an hour and then washed in PPB for 15 minutes 3 times, then incubated in PPB containing anti-tubulin monoclonal antibody at $4^{circ}C$ overnight. And then, the oocytes were incubated with FITC-conjugated anti-mouse IgG and propidium iodide (PI) for 45 minutes. Pattern of microtubules and microfilaments of oocytes were evaluated with a confocal microscope. Results: The rate of oocytes containing normal microtubules and microfilaments was significantly decreased after vitrification. The rate of oocyte containing normal microtubules in CCB treated group was higher than those in non-treated group (53.7% vs. 48.9%), but the difference was not significant. The rate of oocyte containing normal microfilaments in CCB treated group was significantly higher than those in non-treated group (64.5% vs. 38.3%, p<0.05). Conclusion: Microfilaments stability could be improved by CCB treatment prior to vitrification. It is suggested that CCB treatment prior to vitrification improve stability of cytoskeleton and then increase success rate in IVF-ET program using vitrification and thawing oocyte.

• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.343-352
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• 2017

A space plasma facility has been operated with a back-diffusion-type plasma source installed in a mid-sized vacuum chamber with a diameter of ~1.5 m located in Satellite Technology Research Center (SaTReC), Korea Advanced Institute of Science and Technology (KAIST). To generate plasma with a temperature and density similar to the ionospheric plasma, nickel wires coated with carbonate solution were used as filaments that emit thermal electrons, and the accelerated thermal electrons emitted from the heated wires collide with the neutral gas to form plasma inside the chamber. By using a disk-type Langmuir probe installed inside the vacuum chamber, the generation of plasma similar to the space environment was validated. The characteristics of the plasma according to the grid and plate anode voltages were investigated. The grid voltage of the plasma source is realized as a suitable parameter for manipulating the electron density, while the plate voltage is suitable for adjusting the electron temperature. A simple physical model based on the collision cross-section of electron impact on nitrogen molecule was established to explain the plasma generation mechanism.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.361-367
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• 2014

This paper is related to a new solar power conditioner for a built-in step-up chopper function. In the first step-up chopper proposed solar PV power conditioner for mutually connected in series with the input voltage of the bypass diodes are respectively connected to the positive terminal should install the mutual boosting chopper diode connected in series with the boost chopper switching element between the two power supply and at the same time the first and the second was connected to a second diode and a resonance inductor and a snubber capacitor in series with each other. And the common connection point between the bypass diode and the step-up chopper and the step-up chopper diode common connection point of the switching elements of the input voltage was set to the boost inductor for storing energy. In addition, between the step-up chopper and the step-up chopper diode and a switching element of a joint connection point of the first auxiliary diode and the second common connection point of the auxiliary diode was provided, the resonance capacitor. Between the step-up chopper and the step-up chopper diode and a switching element of a joint connection point and the common connection point of the resonance inductor snubber capacitor and connecting the third secondary diode, between two power supply lines is characterized by configuring the DC link capacitor bus lines in parallel. Therefore, it is possible to suppress the switching loss through, DC link bus lines, as well as there could seek miniaturization and weight reduction of the power conditioner itself by using a common capacitor of the non-polar non-polar electrolytic capacitor having a capacitor, the service life of the circuit can be extended and it is possible to greatly reduce the loss can be greatly improve the reliability of the product and the operation of the product itself.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.5 s.120
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• pp.563-568
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• 2007

In this paper, the proposed package antenna, which is meander line structure with short pin, is miniaturized to realize RF-SoP at 900 MHz RFID band. The RFID BGA(Ball Grid Array) chip is put in a cavity of LTCC Layers. The coupling and cross talk, which are happen between BGA chip and proposed package antenna, are reduced by faraday cage, which consists of ground and via fences, is realized to enhance the isolation between BGA chip and antenna. The proposed antenna structure is focused on the package level antenna realization at low frequency band. The novel proposed package antenna size is $13mm{\times}9mm{\times}3.51mm$. The measured resonance frequency is 0.893 GHz. The impedance bandwidth is 9 MHz. The maximum gain of radiation pattern is -2.36 dBi.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.65 no.3
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• pp.194-198
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• 2016

The electric power industry have recently been building out Smart Grids, a two-way electricity grid that connects power consumers and producers to a network that enables one to respond quickly to any eventuality. The construction of a two-way electricity grid means that the power control process becomes unified, from what used to be separate processes that originate individually from the consumption phase and the production and supply phases. The role of power control that takes place within each section of the power system may be independent. However, this does not mean the independent control sections are operated individually, but are configured to meet a single target and purpose. Each control section possesses enough degree of independency to respond to eventualities that may occur within different stages of the power system, but at the same time, possesses unified system elements for the stability of the entire power system. From this perspective, Smart Grids are widely regarded as the most rational power industry operation plan. A variety of different control and communication systems can be applied for an effective deployment of Smart Grids. Recently, we have seen systems such as PMS(Power Management System) and PAS(Process Automation System) applied in the deployment of Smart Grids, which are developed from the techniques utilized in the industry. The PMS is attracting particular attention for its power operations management ability. In this study, we propose plans for improvement in the rational development of power system controls through case studies of live PMS operations.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.372-372
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• 2019

본 논문에서는 격자 기반의 2차원 침수해석 모형인 G2D(Grid based 2-Dimensional land surface flood model)의 GUI 개발에 대해서 기술하였다. G2D 모형은 ASCII 래스터 포맷의 DEM을 이용하여 정형 사각격자로 구성되는 침수모의 도메인을 설정하고, 수위, 수심, 유량 등의 경계조건과 강우와 유량을 연속방정식의 생성항으로 사용하여 2차원 침수모의를 한다. 주요한 침수모의 결과는 ASCII 래스터 포맷을 가지는 수심과 수위 등이다. 이와 같이 G2D 모형은 ASCII 래스터 파일을 주로 이용하고 있다. 본 연구에서는 우선 래스터 파일의 전후처리와 침수모의 결과의 가시화에 대한 편의성을 높이기 위해서 GIS 소프트웨어를 이용하여 GUI를 개발하고자 하였다. 이와 더불어 사용자들이 소프트웨어 구매 비용에 대한 부담을 없애고, 편리하게 사용할 수 있는 오픈소스 소프트웨어를 이용하고자 하였으며, 이 두 가지 조건을 만족할 수 있는 QGIS를 이용해서 G2D 모형의 GUI인 QGIS-G2D를 개발하였다. QGIS-G2D는 QGIS의 plug-in으로 실행된다. QGIS-G2D는 G2D 모형의 실행에 필요한 프로젝트 파일(.g2p)을 GUI를 이용해서 만들 수 있으며, 모의결과를 애니매이션 등으로 가시화 할 수 있는 후처리 기능을 포함하고 있다. 또한 QGIS-G2D는 DEM 수정 기능과 같이 G2D 모형의 입력자료 전처리를 위해서 QGIS plug-in으로 제공되는 여러 가지 기능을 함께 이용할 수 있다. 또한 물리적 분포형 강우-유출 모형인 GRM(Grid based Rainfall-runoff Model)의 QGIS plug-in인 QGIS-GRM과 연계하여, 유역 유출모의와 침수모의를 QGIS 환경에서 함께 수행할 수도 있다. 개발된 소프트웨어는 오픈소스 플랫폼인 GitHub(https://github.com/floodmodel/)를 통해서 제공된다. 본 연구를 통해서 홍수해석에 필요한 강우-유출 모의와 침수모의를 위한 모형을 제공하고, 이를 편리하게 활용할 수 있는 오픈소스 소프트웨어를 제공할 수 있었다. 이러한 연구들은 홍수 분야의 전문가들에 의해서 다양한 분야의 홍수해석에 사용될 수 있을 것으로 기대한다.