• Journal of Energy Engineering
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• v.12 no.2
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• pp.154-163
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• 2003

Grid connection essentially requires a wind energy conversion system (WECS) to not only supply adequate power responding to constantly varying wind speed but also provide a specified level of voltage magnitude and frequency that is acceptable in the electric power network. To satisfy such requirements, appropriate control schemes of a wind turbine to be connected to the power grid should be employed. This paper presents an output control strategy of a grid-connected wind power generation, which consists of a fixed-pitch wind turbine, a synchronous generator and a AC-DC-AC component with a voltage source inverter built in, and performs modelling and analysis of the strategy using PSCAD/EMTDC, an electromagnetic transient analysis software. Real power output control of the voltage source inverter is implemented to extract the maximum energy from wind speed inputted through wind blades and reactive power control, to keep the terminal voltage of WECS at a specific level. SPWM switching method is used to reduce the harmonics and maintain 60 ㎐ of the output frequency. The wind turbine performance and output corresponding to wind variation and the terminal load change is simulated and analysed.

• Journal of the Institute of Convergence Signal Processing
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• v.19 no.3
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• pp.97-103
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• 2018

This paper addresses an improved naval combat UPS(Uninterruptable Power Supply) system under abnormal transients. Previously, thermistor and varistor elements were used to cope with transient overvoltage and overcurrent, however the UPS was frequently unavailable because it was vulnerable to abnormal transient voltage generated during system operation. In order to overcome this problem and protect UPS system, this paper proposes an input power cut-off circuit that detects the initial input power and abnormal transient voltage generated during operation, improvement of power control sequence, and a method to prevent malfunction of an inverter and CPU. The UPS system implementing the proposed method was simulated by input power variable test using programmable AC/DC generator, and finally validated its reliability and stability through field tests by mounting on multifunctional console of naval combat system.

• The Journal of Korean Association of Computer Education
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• v.10 no.6
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• pp.69-77
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• 2007

In this paper we implement main functions of electronic measuring devices, which are essential to design electric/electronic virtual laboratories on the Web. The implemented virtual electronic measuring devices such as virtual analog multimeter(VAM), virtual function generator(VFG), virtual oscilloscope(VOSC) enable the learners to perform the virtual experiments on the Web by simple mouse clicks. In order to show their validity virtual experiments for understanding how to use them are designed. The virtual experiments for measuring resistance(OHM), AC/DC Voltage(ACV/DCV) and DC Current(DCA) by the VAM are illustrated. In addition, the learners can change the frequency of the signal generated from the VFG and measure by the VOSC several types of the signals generated from the VFG such as triangular, pulse, sinusoidal waveforms. The VOSC can measure voltage and current through two channels of it and provide the learners with additional functions such as zooming, trigger, cursor, summing of waveforms. Since the virtual electronic measuring devices have been implemented as forms of Java classes, various types of applications are available according to the structures of virtual laboratories.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.470-475
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• 2019

This paper deals with a 30kW grid-connected PCS (Power Conversion System) for an Oscillating Water Column (OWC) wave-power generation system. Wave power generation in marine energy is suitable for Korea with the characteristics of a peninsula with three sides facing the sea. In the case of coastal disasters, wave generators can act as a breakwater to reduce damage, and can be integrated with other marine power generation systems to increase efficiency. Wave power generation systems are classified into various types, such as oscillating bodies, OWC, and overtopping according to the operation principle, and they can also be classified into two types according to the installation method: a fixed structure and floating structure. This paper proposes a 30kW grid-connected PCS topology and model for OWC wave power generation that is structurally stable with a turbine and generator that are relatively easy to maintain, and then provide a control method required for grid connection, including DC link voltage control. Simulation verification was performed to verify the proposed PCS.

• Journal of IKEEE
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• v.23 no.1
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• pp.289-294
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• 2019

At present, domestic small islands mainly supply electric power using diesel generators. However, diesel generators can cause instability of the power system due to slow response on power load fluctuation, and cause environmental problems due to the emission of carbon gas by using fossil fuels. In order to overcome this problem, this paper proposes a method to establish an optimal microgrid by introducing solar power, wind power, and energy storage device to Chujado Island, which is supplied with electric power through a diesel generator. The economical optimum capacity of each distributed power source is calculated by using HOMER (Hybrid Optimization Model for Multiple Energy Resources) program and the proposed microgrid is validated by using PSCAD/EMTDC (Power Systems Computer Aided Design/ Electromagnetic Transients including DC) program which can analyze system stability.

• Journal of the Korean Society of Safety
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• v.30 no.4
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• pp.39-45
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• 2015

This paper deals with development of integrity evaluation instrument for the power line surge protective device. A reliable power supply is an essential element in the developed information and communication society by highly advances in IT technology. However, the lightning incidence also increased with the recent extreme weather events. In Korea, in order to protect the electrical system from lightning surge, SPD(Surge Protective Device) has been used for these past 30 years. However, the method of diagnosing the safety of the SPD in the industry is insufficient. In this paper, SPD integrity evaluation system was composed of a variable DC power source unit, voltage-current sensor and the embedded controller. In order to measure V-I characteristics of MOV, 3 type samples were degraded by impulse current generator. After impulse tests, the varistor voltage of all samples and nonlinearity coefficient were decreased. It confirmed the utility of the developed equipment by this experimental test and the reliability of SPD is expected for surge accident prevention when applied to industrial plant.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.10
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• pp.103-109
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• 2003

We have proposed the 4-Dimensional Multiple-Subcarrier Modulation with fixed bias in Optical Wireless Communications. Here, the 4-D signal vectors are derived from the optimization technique of signal waveforms maximizing the minimum distance between signal points in an n-dimensional Euclidean sphere. The resulting vectors are used in generating the output amplitude of impulse generator in a Multiple-Subcarrier Modulation scheme. We have achieved that the normalized power requirement of the proposed system is maximum 3 dB and 3.3 dB smaller than those of normal QPSK, Reserved Subcarrier, and Minimum Power scheme, respectively. Also, in the range of 1.125 ∼ 1.25 of the normalized bandwidth, the proposed system has maximum 3 dB, 2 ∼ 4 dB, 0 ∼ 3 dB smaller bandwidth requirement compare to normal QPSK, Res. Subcarrier, Min. Power schemes, respectively.

• Analytical Science and Technology
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• v.5 no.1
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• pp.91-96
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• 1992

A simple and cheap AC voltammeter was manufactured in our lab. This instrument consists of a DC function generator and a lock-in amplifier. We tested this instrument in some chemical systems. Our data, CV voltammogram and AC voltammogram, obtained form using a Pt working electrode in 1M $H_2SO_4$ and a reversible system of $1{\times}10^{-3}M$ ${Fe(CN)_6}^{3-}$ proved our system works well. The quantitative result of iodine is also obtained.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.2004-2012
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• 2014

Energy storage devices are necessary to obtain stable utilization of renewable energy sources. When black-out occurs, distributed renewable power sources with energy storage devices can operate under standalone mode as uninterruptable power supply. This paper proposes a dynamic response analysis with small-signal modeling for the standalone operation of a photovoltaic power generation system that includes a bidirectional charger/discharger with a battery. Furthermore, it proposes a DC-link voltage controller design of the entire power conditioning system, using the storage current under standalone operation. The purpose of this controller is to guarantee the stable operation of the renewable source and the storage subsystem, with the power conversion of a very efficient bypass-type PCS. This paper presents the operating principle and design guidelines of the proposed scheme, along with performance analysis and simulation. Finally, a hardware prototype of 1-kW power conditioning system with an energy storage device is implemented, for experimental verification of the proposed converter system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.9
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• pp.1219-1226
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• 2014

This paper introduces a hardware simulator for the LVRT operation analysis of the grid-tied PMSG wind power system with a power dissipation circuit. The power dissipation circuit, which is composed of chopper and resistor, suppresses the sudden increase of DC-link voltage in the back-to-back converter of the grid-tied PMSG wind power system. The LVRT operation was first analyzed using computer simulations with PSCAD/EMTDC. A wind power simulator including the power dissipation circuit and the fault simulator composed of variac and IGBT were built to analyze the LVRT operation. Various experiments were conducted to verify the effectiveness of the power dissipation circuit for the LVRT operation. The developed hardware simulator can be extensively utilized for the analysis of various LVRT operations of the grid-tied wind power system.