• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.10
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• pp.1081-1091
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• 1992

A new method for designing of WDF(Wave Digital Filter) is proposed, which is based on the digital dependent port adaptor transformed by the VGIC(Voltage Conversion Generalized Impedance Converter). To design the WD-LPF, WD-BPF, WD-HPF, or WD-BRF with CGIC(Current Conversion GIC). we have to use the different structure respectively. But the proposed method to design any types of WDF requires only one universal WDF structure, and this structure is attractive for its VLSI implementation for its simplicity.

• Journal of Power Electronics
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• v.14 no.3
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• pp.572-579
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• 2014

As a non-linear time variant system, the four-quadrant line converter of an electric multiple unit (EMU) was expressed by linear time periodic functions near an operating point and modeled by a steady-state harmonic domain matrix. The components were then combined according to the circuit connection and relations of the feedback control loops to form a complete converter model. The proposed modeling method allows the study of the amplitude of harmonic impedances to explore harmonic coupling. Moreover, the proposed method helps provide a better design for the converter controllers, as well as solves the problem in coordination operation between the EMUs and the AC supply. On-site data from an actual $CRH_2$ high-speed train were used to validate the modeling principles presented in the paper.

• Journal of Electrical Engineering and Technology
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• v.2 no.2
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• pp.249-256
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• 2007

This paper presents a new circuit topology and its digital control scheme for a half-bridge resonant inverter. As the proposed half-bridge inverter can be operated in load-freewheeling modes, the pulse-width modulation (PWM) method can be used for the output power control. The proposed half-bridge inverter is based on the resonant frequency-tracking algorithm with the goal of maintaining the unity of the output displacement factor of the load impedance even in varying conditions. In this paper, the operation principle, electrical characteristics, and detailed digital control scheme of the proposed half-bridge resonant inverter are described. The experimental results of the prototype experimental setup to verify the validity of the proposed half-bridge inverter are presented and discussed.

• The Journal of Korea Robotics Society
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• v.14 no.4
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• pp.311-317
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• 2019

Direct teaching is an essential function for collaborative robots for easy use by non-experts. For most robots, direct teaching is implemented only in joint space because the realization of Cartesian space direct teaching, in which the orientation of the end-effector is fixed while teaching, requires a measurement of the end-effector force. Thus, it is limited to the robots that are equipped with an expensive force/torque sensor. This study presents a Cartesian space direct teaching method for torque-controlled collaborative robots without either a force/torque sensor or joint torque sensors. The force exerted to the end-effector is obtained from the external torque which is estimated by the disturbance observer-based approach with the friction model. The friction model and the estimated end-effector force were experimentally verified using the robot equipped with joint torque sensors in order to compare the proposed sensorless approach with the method using torque sensors.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.98-107
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• 2000

Free-field ground motion during earthquake is significantly affected by the local site conditions and it is essential for the seismic design to perform the ground response analysis In this study, ground response analyses based on the equivalent linear method were carried out to evaluate the effects of various ground conditions on the site amplification. Four major factors including the depth of the site(very soft and dense soil), the impedance ratio between soil layer and bed rock, linear analysis versus equivalent linear analysis, and the location of soft soil layer were deeply discussed. Based on the analysis results, the importance of various local site conditions on the site amplification was emphasized.

• Proceedings of the KIPE Conference
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• 1997.07a
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• pp.211-215
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• 1997

Localized communication networks for office automation, security monitoring, environmental management of buildings, computer communications, and other applications enjoy every increasing demand. This paper proposes a direct sequence spread spectrum communication system for use in power line data transmission. Advantages of power distribution circuits include reasonably universal coverage and easy access vis a standard wall plug. Disadvantages include limited communication bandwidth, relatively high noise levels, and varying levels of impedance, noise, and attenuation. Spread spectrum signalling provides immunity to narrow-band signal impairments and multiplexing capability. Our prototype power line communication module supports completely physical and data link layers based on the international standard ISO 10368 for reliable high-speed power line communication system. Moreover it provides useful functions to compose a plant monitoring and control system. All the circuits of the communication module are included in one compact circuit. Thus a functional communication system for the power line plant monitoring and control is implemented.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.601-608
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• 1989

Electrical properties of ZrF4-based heavy metla fluoride glasses were measured by the ac complex impedance method. The effects of alkali and chloride ions addition into fluoro zirconate glasses on the electrical conductivity were examined. The electrical conductivities of fluoride glasses show Arrhenian behavior in the temperature range of the experiment and were decreased by the addition of sodium fluoride up to 15mol%. Mixed alkali substitution resulted in conductivity minimum at intermediate composition which is commonly observed as mixed alkali effect' in alkali oxide glasses. Chloride ion substituted for fluoride ion was found to lower the conductivity.

• Journal of Power Electronics
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• v.18 no.4
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• pp.1190-1200
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• 2018

A current sourced bi-directional wireless power transfer (WPT) system is proposed to solve the problems that exist in the bi-directional WPT for vehicle-to-grid (V2G) systems. These problems include the fact that these systems are not safe enough, the output power is limited and the control methods are complicated. Firstly, the proposed system adopts two different compensation and control methods on both the primary and secondary sides. Secondly, based on an AC impedance analysis, the working principle is analyzed and the parameter configuration method with frequency stability is given. In order to output a constant voltage, a bi-directional DC/DC circuit and a controllable rectifier bridge are adopted, which are based on the "constant primary current, constant secondary voltage" control strategy. Finally, the effectiveness and feasibility of the proposed methods are verified by experimental results.

• Electrical & Electronic Materials
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• v.9 no.8
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• pp.831-835
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• 1996

The molten carbonate fuel cell has conspicuous features and high potential in being used as an energy converter of various fuels to electricity and heat. However, the MCFC which use strongly corrosive molten carbonate at 650[.deg. C] have many problem. Systematic investigation on corrosion behavior of Fe-based Cr has been done in ($62{\times}38$)mol % (Li+K)$CO_3$ melt at 923K by using steady state polarization and electrochemical impedance spectroscopy method. It was found that the corrosion current of these Fe-based alloys decreased with increasing Cr content, and this was attributed to the formation of $LiCrO_2$ layer at the surface .

• Proceedings of the KIEE Conference
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• 2001.05a
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• pp.34-37
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• 2001

This paper presents some results after comparing the characteristics of 3 algorithms, which are discrete Fourier transform based algorithm, least square method, and modified differential approximation algorithm, used at most distance relays all over the world. In case of the DFT based distance relaying algorithm, the length of the algorithm data window and the cut-off frequency of an anti-aliasing low-pass filter adopted are fixed. On the other hand, the data window lengths are changed according to the corresponding low-pass filters in the rest two algorithms. In series of tests, the apparent impedance estimated by the modified differential approximation algorithm shows faster and more stable characteristics of convergence than the two others.