• The Transactions of the Korean Institute of Electrical Engineers P
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• v.67 no.2
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• pp.112-118
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• 2018

In recent years, decentralized power have been increasing due to environmental problems, liberalization of electricity markets and technological developments. These changes have led to the evolution of power generation, transmission, and distribution into discrete sectors and the division of integrated power systems. Therefore, studies are underway to efficiently supply power and reduce losses to each sector's demand. This is a major concern for system planners and operators, as it accounts for a relatively high proportion of total power, with a transmission and distribution loss of 4-6%. Therefore, this paper analyzes the status of loss management based on the current transmission and distribution loss rate of each country and transmission loss management cases of each national power company, and proposes a loss rate prediction algorithm according to the long-term transmission system plan. The proposed algorithm predicts the demand-based long-term evolution and the loss rate of the grid to which the transmission plan is applied.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1743-1751
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• 2016

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.6
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• pp.23-29
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• 2014

In this study, cooling and heat-transfer tests are performed to compare and evaluate the thermal conductivity in a prepared CNT TIM (thermal interface material). A polymerized CNT heat-transfer resin and commercial thermal grease (Shinetsu G-747) were applied for a comparison test in both cases. Cooling experiments with an aluminum foil specimen were performed in order to measure the temperature distribution using an infrared camera, and in heat radiation experiments, performance testing of the thermal conductivity was conducted using high-power LEDs. Carbon resin with the polymerization of graphite and carbon black, and CNT-polymerized CNT resin with graphite and carbon black were tested and compared with using G-747. It was found that the cooling performance and the heat transfer ability in both the carbon resin and the CNT-polymerized CNT resin were greater than those of G-747 because the temperature by 5. $0^{\circ}C$ in both cases appeared lower than that of the G-747.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.295-299
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• 2012

We investigated the crystal and the optical properties of GaN-based blue light emitting diodes (LEDs) which were simultaneously grown on c-plane (0001) and semipolar (11-22) GaN templates by using metal-organic chemical vapor deposition (MOCVD). The X-ray rocking curves (XRCs) full width at half maximums (FWHMs) of c-plane (0001) and semipolar (11-22) GaN templates were 275 and 889 arcsec, respectively. In addition, high-resolution X-ray ω-2θ scan showed that satellite peaks of semipolar (11-22) InGaN quantum-wells (QWs) was weaker and broader than that of c-plane (0001) InGaN QWs, indicating that the interface quality of c-plane (0001) QWs was superior to that of semipolar (11-22) QWs. Photoluminescence (PL) and electroluminescence (EL) results showed that the emission intensity and the FWHMs of polar c-plane (0001) LED were much higher and narrower than those of semipolar (11-22) LED, respectively. From these results, we believed that relative poor crystal quality of semipolar (11-22) GaN template might give rise to the poor interfacial quality of QWs, resulting in lower output power than conventional c-plane (0001) GaN-based LEDs.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.92-97
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• 2007

This paper performed the basic study for developing the Photodynamic Therapy Equipment for medical treatment. We developed the equipment palpating cell proliferation using a high brightness LED. This equipment was fabricated using a micro-controller and a high brightness LED, and designed to enable us to control light irradiation time, intensity, frequency and so on. Especially, to control the light irradiation frequency, FPGA was used, and to control the change of output value, TLC5941 was used. Control stage is divided into 30 levels by program. Consequently, the current value could be controlled by the change of level in Continue Wave(CW) and Pulse Width Modulation(PWM), and the output of a high brightness LED could be controlled stage by stage. And then, each experiment was performed to irradiation group and non-irradiation group for both Rat bone marrow and Rat tissue cells. MTT assay method was chosen to verify the cell increase of two groups and the effect of irradiation on cell proliferation was examined by measuring 590 nm transmittance of ELISA reader. As a result, the cell increase of Rat bone marrow and tissue cells was verified in irradiation group as compared to non-irradiation group. The fact that specific wavelength irradiation has an effect on cell vitality and proliferation is known through this study.

• Korean Journal of Optics and Photonics
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• v.31 no.2
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• pp.81-87
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• 2020

This study examines the design technology of searchlight optics featuring narrow beam angles and high luminous intensities. Halogen and xenon lamps, which are conventional searchlight sources, are vulnerable to vibration and shock, and are large and heavy, making them difficult to transport. In addition, the parabolic mirror located at the rear of the searchlight has the disadvantages of poor performance and low light efficiency, due to the assembly error produced during manufacturing. To solve this problem, a 1-kW halogen lamp is replaced by a 150-W high-power COB LED, and a high-efficiency TIR lens is designed to meet the target performance. Afterward, the TIR lens array is proposed to solve the surface error generated during optical injection. After a prototype is manufactured based on the designed optical system, the optical performance is confirmed to be excellent, by comparing it to that of a commercial halogen-lamp searchlight.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.12
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• pp.1071-1076
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• 2008

This paper presents the self power generation from vibration using the piezoelectric bimorph actuator. The piezoelectric bimorph actuator was well developed with PZT-PNN-Fe piezoelectric ceramics. As the applied voltage was increased, a linear change of displacement was obtained with a relatively high ratio of 12.53 um/V for the bimorph actuator. Moreover, when the motor's rotational speed was 2000 rpm, the bimorph actuator, which has a resonance frequency of 68 Hz, exhibited the most efficient generation voltage of 10.4 V. This bimorph actuator could make the LED, emitting 60 mW, working successfully. Therefore, it is anticipated that the bimorph actuator will be useful as a power source for the next-generation electronic devices.

• Journal of Korean Society of Water and Wastewater
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• v.18 no.3
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• pp.351-356
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• 2004

Selecting appropriate G values in flocculator operation is important to produce high quality filter effluent in water treatment plants. However, misunderstanding and misleading of G calculation for the case of having power sources more than one or many paddles with one power source in a flocculation basin sometimes have led to low performance in flocculation. Theoretical analysis confirmed that the total G value in one flocculation unit having power sources more than one or with many paddles is the root-square of the sum of square of individual G value. This analysis also can give a simple calculation method of G value for designers and operators in fields.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.10
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• pp.653-656
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• 2014

$Cs_3Sb$ photocathode was formed by newly developed process and successive in-situ lighting devices were fabricated in a process chamber. R, G, and B phosphors were applied on the anode plate, respectively. Major parameters such as brightness, power consumption, and efficacy were measured. The wavelength of LED excitation source was 450 nm. Both high power and low power modes were applied in the measurement. Measurement values were clearly differentiated by the voltage application modes. The measured values of each parameter was good enough to be applied for general lighting source. The results showed that $Cs_3Sb$ photocathode formed in atmospheric conditions was functioning as good as the photocathode formed in UHV conditions, and thus it could be applied to advanced lighting devices.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.356-357
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• 2003

Organic materials are suitable for use in photoelectric conversion devices. Thus, Organic semiconductors are promising materials for photovoltaic devices and other optoelectronic applications such as light emitting diodes(LED). The organic solar cell seems to be the usefulness in comparison with the inorganic solar cell in terms of workability, ease of processing, low cost, flexibility and area expansion. (omitted)