• Journal of the Korean Society of Safety
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• v.28 no.5
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• pp.10-14
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• 2013

This paper is aimed to investigate the actual conditions of standalone PV(Photovoltaics) streetlight in public place and analyze cause of failure and derive the method of decrease for standalone PV streetlight. The cost of installing standalone PV streetlight in a public for the safety and convenience of life is expensive(300 million won per unit). Management of standalone PV streetlight is important because it is operating system itself, after installation, but concern degree of management is very low and development of technology has not been done. Accordingly, standalone PV streetlight in public place is not operate in night, this phenomenon is lasted for several days to months. Therefore this study, for standalone PV streetlight constantly to keep the normal operation, investigation conducted to check status of standalone PV streetlight(50 units), the voltage of the main parts and analyze the cause of the failure. In addition, the improvement of standalone PV streetlight is suggested by using FTA(fault tree analysis).

• Advances in nano research
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• v.2 no.1
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• pp.23-56
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• 2014

The significant growth of the Si photovoltaic industry has been so far limited due to the high cost of the Si photovoltaic system. In this regard, the most expensive factors are the intrinsic cost of silicon material and the Si solar cell fabrication processes. Conventional Si solar cells have p-n junctions inside for an efficient extraction of light-generated charge carriers. However, the p-n junction is normally formed through very expensive processes requiring very high temperature (${\sim}1000^{\circ}C$). Therefore, several systems are currently under study to form heterojunctions at low temperatures. Among them, carbon nanotube (CNT)/Si hybrid solar cells are very promising, with power conversion efficiency up to 15%. In these cells, the p-type Si layer is replaced by a semitransparent CNT film deposited at room temperature on the n-doped Si wafer, thus giving rise to an overall reduction of the total Si thickness and to the fabrication of a device with cheaper methods at low temperatures. In particular, the CNT film coating the Si wafer acts as a conductive electrode for charge carrier collection and establishes a built-in voltage for separating photocarriers. Moreover, due to the CNT film optical semitransparency, most of the incoming light is absorbed in Si; thus the efficiency of the CNT/Si device is in principle comparable to that of a conventional Si one. In this paper an overview of several factors at the basis of this device operation and of the suggested improvements to its architecture is given. In addition, still open physical/technological issues are also addressed.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.3
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• pp.206-212
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• 2008

This paper proposes the PLL(Phase-Locked Loop) algorithm by a new FFT(Fast Fourier Transform) in a grid-connected PV PCS(Photovoltaics Power Conditionning System). The grid-connected inverter that is applied in a new renewable energy field needs the grid phase information for synchronism. Unlike the PLL which is normally used by three phase D-Q conversion, the preposed PLL algorithm using FFT has non-gain tuning and the powerful noise elimination by the characteristics of FFT. Both simulation and experimental result show that proposed algorithm has the good capacity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.159-159
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• 2008

Indium-tin oxides (ITO) films have been widely used as transparent electrodes for optoelectronic devices such as organic light emitting diodes (OLEDs), photovoltaics, touch screen devices, and flat-paneldisplay. In particular, to improve hole injection efficiency in OLEDs, transparent electrodes should have high work-function besides their transparency and low resistivity. Nevertheless, few studies have been made on engineering the work function of ITO for use as an efficient anode. In this study, the effects of a wide range of Nb or Zn doping rate on the changes in work functions of ITO anode were investigated. The Nb or Zn doped ITO films were fabricated on glass substrates using combinatorial sputtering system which yields a linear composition spread of Nb or Zn concentration in ITO films in a controlled manner by co-sputtering two targets of ITO and Nb2O5 or ITO and ZnO. We have also examined the resistivity, transmittance, and other structural properties of the Nb or Zn-doped ITO films. Furthermore, OLEDs employing Nb or Zn-doped ITO anodes were fabricated and the device performances were investigated concerned with the work function changes.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.1
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• pp.171-177
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• 2021

In terms of distribution planning, accurate electric load prediction is one of the most important factors. The future load prediction has manually been performed by calculating the maximum electric load considering loads transfer/switching and multiplying it with the load increase rate. In here, the risk of human error is inherent and thus an automated maximum electric load forecasting system is required. Although there are many existing methods and techniques to predict future electric loads, such as regression analysis, many of them have limitations in reflecting the nonlinear characteristics of the electric load and the complexity due to Photovoltaics (PVs), Electric Vehicles (EVs), and etc. This study, therefore, proposes a method of predicting future electric loads on distribution lines by using Machine Learning (ML) method that can reflect the characteristics of these nonlinearities. In addition, predictive models were developed based on actual data collected at KEPCO's existing distribution lines and the adequacy of developed models was verified as well. Also, as the distribution planning has a direct bearing on the investment, and amount of investment has a direct bearing on the maximum electric load, various baseline such as maximum, lowest, median value that can assesses the adequacy and accuracy of proposed ML based electric load prediction methods were suggested.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.5
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• pp.348-356
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• 2021

Field-effect transistors (FETs) are the key elements of conventional electronics; hence, have drawn a lot of research and commercial interests. In recent years, metal halide perovskite materials have achieved a remarkable efficiency of 29.15% in the field of photovoltaics, and have drawn the scientific community's attention to promote their use in the field of optoelectronics, such as FETs and phototransistors. The MAPbI₃ (methylammonium lead iodide) perovskite TFT has achieved a record hole mobility of 21.41 cm²/V-s in the year 2020. In this review, we will briefly discuss the physical structure of MAPbI₃ perovskite and the essential factors that stimulate these devices, together with the role of defects, the ion migration concept, and the implication of both dielectric and electrode materials on the device's performance.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.4
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• pp.483-491
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• 2012

It is expected that, in the future, DC power service will be widely used for photovoltaic home power generation systems, since DC consuming devices are ever increasing. Instead of using multiple converters to convert DC to AC and then AC to DC, the power service could solely be based on DC. This would eliminate the need for converters, reducing the cost, complexity, and possibly increasing the efficiency. However, configuration of direct DC power service with mechanical contacts can cause spark voltage or an electric shock when the switch is turned on and off. To solve these problems, in this paper, a contactless power supply for a DC power service that can transfer electric power produced by photovoltaics to the home electric system using magnetic coupling instead of mechanical contacts has been proposed. The proposed system consists of a ZVS boost converter, a half-bridge LLC resonant converter, and a contactless transformer. This proposed contactless system eliminates the use of DC switches. To reduce the stress and loss of the boost converter switching devices, a lossless snubber with coupled inductor is applied. In this paper, a switching frequency control technique using the contactless voltage sensing circuit is also proposed and implemented for the output voltage control instead of using additional power regulators. Finally, a prototype consisted of 150W boost converter has been designed and built to demonstrate the feasibility of the proposed contactless photovoltaic DC power service. Experimental results show that 74~83% overall system efficiency is obtained for the 10W~80W load.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.16 no.4
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• pp.27-40
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• 2013

These day morden cities have serious climatic problems due to enviornmental load caused by excessive development of urbanization. As technological improvement to answer to various ecological disasters and climate changes are also called on the field of construction, inter-disciplinary studies linked to the estabilishment of sustainable energy generation systems and enviornmental control is needed in a consilient point of view. This study aims to analyse optimal site conditions for photovoltaic system and green roof planting through solar radiation simulation in a integrated perspective. In so doing, it seeks to proffer basic study for developing a sound use of roof area that is sustainable in environmental and resources aspects. A computer simulation showed that, in the case of total seasonal solar radiation, summer season resulted 312.5kWh in 35% of total annual solar radiation. This season indicated the lowest radiation rate of the year for direct sunlight in 45.8% of total seasonal solar radiation. Due to such solar radiation simulation, at the largest optimal planting area, Glechoma hederacea var. longituba secured $719.16m^2$ of gross roof area.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.185-185
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• 2011

ZnTe semiconductor is very attractive materials for optoelectronic devices in the visible green spectral region because of it has direct bandgap of 2.26 eV. The prototypes of ZnTe light emitting diodes (LEDs) have been reported [1], showing that their green emission peak closely matches the most sensitive region of the human eye. Another application to photovoltaics proved that ZnTe is useful for the production of high-efficiency multi-junction solar cells [2,3]. By using the pulse laser deposition system, ZnTe thin films were deposited on ZnO thin layer, which is grown on (0001) Al2O3substrates. To produce the plasma plume from an ablated ZnO and ZnTe target, a pulsed (10 Hz) YGA:Nd laser with energy density of 95 mJ/$cm^2$ and wavelength of 266 nm by a nonlinear fourth harmonic generator was used. The laser spot focused on the surface of the ZnO and ZnTe target by using an optical lens was approximately 1 mm2. The base pressure of the chamber was kept at a pressure around $10^{-6}$ Torr by using a turbo molecular pump. The oxygen gas flow was controlled around 3 sccm by using a mass flow controller system. During the ZnTe deposition, the substrate temperature was $400^{\circ}C$ and the ambient gas pressure was $10^{-2}$ Torr. The structural properties of the samples were analyzed by XRD measurement. The optical properties were investigated by using the photoluminescence spectra obtained with a 325 nm wavelength He-Cd laser. The film surface and carrier concentration were analyzed by an atomic force microscope and Hall measurement system.

• The Journal of Korean Institute for Practical Engineering Education
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• v.3 no.2
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• pp.75-82
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• 2011

Recently the technology of green growth became more important role among the problems of running out of fossil fuels and global warming. To procure a new growth power combined with energy and green growth, a lot of investment for wind power, photovoltaics system, fuel cell and biofuel expanded day by day. Among these, wing power has a merit of a highly economic and no discharge of toxic substance. These days government and industrial companies actively support the development of wind power technology with lots of investment, but domestic related education and equipment still stay in research level when it is compared with foreign advanced countries which lead the wind power technology. Therefore to expand the base of basic skill required in the related industrials and to advance technology, we are in the situation to be needed a development of a new curriculum and educational equipment which is analogous with the actual industrial system. In this paper a development of a new educational equipment for the learning of turbine control is introduced. This educational equipment has been developed for students to get easy understanding for the theory of wind turbine control. And finally to demonstrate the effect of the use of the developed equipments and curriculum a questionnaire carried out.