• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.107-109
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• 1995

This paper considers backing structure of non-contact steel plate using magnectically levitation and aspect-quality factor is defined by estimation of electromagnet-aspect attraction steel plate. Characteristics of attraction power is studied in cylindrical electromagnet, U-type electromagnet, E-type electromagnet by aspect-quality factor. Designing and manufacturing electromagnet attraction steel plate, propriety of experimental results is confirmed.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.576-580
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• 2001

This paper presents a casca multilevel PWM rectifier without the isolation transformers for energy build-up at each inverter modules; The features and advantages of the proposed PWM rectifier can be summarized as follows; 1) It realizes the high power high voltage AC/DC power conversion, 2) It uses no transformer which is bulky and heavy, 3) It has hybrid structure so that switching devices can be effectively utilized, 4) It produces high quality AC current even in high power high voltage applications, 5) The input power factor remains unity by simple modulation index control. The multilevel rectifier is analyzed by using the circuit DQ transformation whereby the characteristics and control equations are obtained. Finally, it will be shown that the system simulation reveals the validity of analyses

• Journal of Electrical Engineering and Technology
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• v.3 no.3
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• pp.320-330
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• 2008

This paper presents an improved dynamic programming (IDP) approach to solve the economic power dispatch problem including transmission losses in power systems. A detailed mathematical derivation of recursive dynamic programming approach for the economic power dispatch problem with transmission losses is presented. The transmission losses are augmented with the objective function using price factor. The generalized expression for optimal scheduling of thermal generating units derived in this article can be implemented for the solution of the economic power dispatch problem of a large-scale system. Six-unit, fifteen-unit, and forty-unit sample systems with non-linear characteristics of the generator, such as ramp-rate limits and prohibited operating zones are considered to illustrate the effectiveness of the proposed method. The proposed method results have been compared with the results of genetic algorithm and particle swarm optimization methods reported in the literature. Test results show that the proposed IDP approach can obtain a higher quality solution with better performance.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.569-574
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• 1998

This paper presents a two-paralleled 4 quadrant DC chopper type PWM power conversion circuit in order to generate a gradient magnetic field in the Magnetic Resonance Imaging (MRI) system. This power amplifier is connected in parallel with the conventional 4-quadrant DC chopper using IGBTs at their inputs/outputs to realize further high-power density, high speed current tracking control, and to get a low switching ripple amplitude in a controlled current in the Gradient Coils (GCs). Moreover, the power conversion circuit has to realize quick rise/fall response characteristics in proportion to various target currents in GCs. It is proposed in this paper that a unique control scheme can achieve the above objective. DSP-based control systems realize a high control facility and accuracy. It is proved that the new control system will greatly enlarge the diagnostic target and improve the image quality of MRI.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.194-199
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• 1996

Grinding burn formed on the ground surface is related to the maximum temperature of workpiece surface and wheel temperature in the grinding process. The thermal characteristics of workpiece and grinding conditions on the surface temperature of the oxidation growing layer after get out of contact with the grinding wheel. The assumption used in grinding power signatures leads to the local temperature distribution between grinding wheel and workpiece, i.e., a single curve determines temperatures anywhere within the grinding wheel at anytime. This information is useful in the study of the grinding bum penetration into the wheel and thus provides an presentation of grinding trouble monitoring for the burning. On the basis of grinding power signatures in the wheel, thermally optimum conditions are defined and controlled. To cope with grinding burn, the use of grinding power signatures is an effective monitoring systems when occurring the grinding process. In this paper, the identified parameters suggested in this study which are derived from the grinding power signatures are presented.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.312-316
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• 2014

In this paper, a voltage sag is analyzed in case of superconducting fault current limiter (SFCL) installed in power distribution system where replaces the main power transformer to large one to meet the power demand. First, the power system is configurated to analyze the operation characteristics of the protective relay with replacement of the main transformer and application of the SFCL. Next, the method to meet the protection coordination is analyzed with large transformer using PSCAD/EMTDC. Finally, the bus voltage is investigated according to the impedance of both main transformer and SFCL in case that the SFCL is applied into feeder.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.427-431
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• 2000

ITO (indium tin oxide) thin films on PET (polyethylene terephthalate) and glass substrates have been deposited by a dc magnetron sputtering without heat treatments such as substrate heater and post heat treatment. Each sputtering parameter during the sputtering deposition is an important factor for the high quality of ITO thin films deposited on polymeric substrate. Particularly, the material, electrical and optical properties of as-deposited ITO oxide films are dominated by sputtering power, oxygen partial pressure and films thickness. As the experimental results, the XRD patters of ITO films are influenced by sputtering power and pressure. As the power and pressure are increased, (411) peak is grown suddenly. the electrical resistivity is also increased, as the sputteing power and pressure are increased. Transmittance of ITO thin films in visible light ranges is lowered with increasing the sputtering power and film thickness. Reflectance of ITO films in infia-red region is decreased, as the power and pressure is increased.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.4
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• pp.582-588
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• 2008

Microgrids are new distribution level power networks that consist of various electronically-interlaced generators and sensitive loads. The important control object of Microgrids is to supply reliable and high-quality power even during the faults or loss of mains(islanding) cases. This paper presents power control methods to coordinate multiple distributed generators(DGs) against abnormal cases such as islanding and load power variations. Using speed-droop and voltage-droop characteristics, multiple distributed generators can share the load power based on locally measured signals without any communications between them. This paper adopts the droop controllers for multiple DG control and improved them by considering the generation speed of distribution level generators. Dynamic response of the proposed control scheme has been investigated under severe operation cases such as islanding and abrupt load changes through PSCAD/EMTDC simulations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.565-568
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• 2002

Welding variables and conditions in gas metal arc welding (GMAW) effect on the weld quality and productivity, extensive research efforts have been made to analyze the welding variables and conditions. In this study dynamic behavior of GMAW system is investigated using the characteristic equations of the power supply, wire and welding arc. Characteristic equation of wire is modified to include the effect of droplets attached at the electrode tip. The dynamic characteristics of arc length, current, voltage with respect to the step, ramp inputs of CTWD was simulated, seam tracking procedure using arc sensor was simulated with variable V-Groove geometries and weaving frequencies. From results of simulation, some predictions about dynamic characteristics of GMAW and welding process are available. The proposed simulator and results appear to be utilized to determine the proper welding conditions, to be improved by considering power supply dynamic characteristics.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.4
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• pp.639-643
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• 2009

A reformer, which produces hydrogen from natural gas, plays a major role for producing quality hydrogen to fuel-cell system. In this paper, fuel processor is designed to deliver hydrogen(75%) from the reformer to 200W fuel-cell system, and the electrical output power of the fuel-cells is examined by being injected different hydrogen concentrations to the system. We verified that the output power characteristics of the fuel-cells with 75% reformed hydrogen was lower about 7% than the case of pure hydrogen supplied. The type of reformer in this experiment takes SMR(Steam methane reforming) process, and the temperature variation characteristics of reforming process by reactions are examined in operation.