• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.71-72
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• 2011

This paper presents a novel and direct dead time compensation method of the 3 phase inverter using space vector pulse width modulation(SVPWM) topology. In the turn on time calculation of the effective voltage, the dead time effect is directly compensated according to the current direction of the midium voltage reference. Since the turn on time of the effective voltage vector is affected by the dead time, the loss time is compensated to turn on time of the effective voltage vector. And the dead time is added to the calculated voltage vector switching times according to the current direction. For the more effective compensation, the direction of the midium phase current is considered by the practical direction and voltage drops in the power devices. The proposed method can compensate the dead time which is considered feedback error or direction of middle phase current without coordinate transform in added controller. The proposed dead time compensation scheme is verified by the computer simulation and experiments of 3 phase R L load.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.4
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• pp.329-332
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• 2020

A back-electromotive force (back-EMF) estimator for a permanent magnet synchronous motor (PMSM) uses the three-phase voltage references of a current controller to estimate rotor position. However, owing to voltage drops caused by the nonlinear characteristics of switches and passive components, the actual voltage in the motor and the three-phase voltage reference may not match. This study proposes a sensorless control method using a sine-wave output filter applied between the motor drive system and PMSM. The precise voltage in the motor can be measured with the sine-wave output filter and applied to the input of the estimator. Moreover, given that the voltage in the motor can be measured precisely at extremely low speeds, the stable operation range of the back-EMF estimator can be secured. Experimental results show that the proposed sensorless control method has stable operation at extremely low speeds compared with conventional sensorless control.

• Journal of Environmental Science International
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• v.10 no.5
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• pp.351-358
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• 2001

The main purpose of this study was to investigate the characteristics of cylindrical electrostatic precipitator with centrifugal effect in viewpoints of pressure drip and collection efficiency, experimentally. The experiment was carried out for the analysis of current-voltage, pressure drop and collection efficiency with various experimental parameters such as the applied voltage, inlet velocity, inlet size and inlet type(upper and bottom), etc. In the results, the pressure drops were estimated as 27~54, $34~63mmH_2O$ for inlet size $15mm{\tiems}30mm$ and $30mm{\tiems}60mm$, respectively. The collection effeciencies were shown over 90% with the small inlet size($15mm{\tiems}30mm$) for the applied voltage 40kV, inlet velocity(15~21m/s), and 51~89% with the large inlet size ($30mm{\tiems}60mm$). Moreover, in the applied voltage 0kV and inlet size $15mm{\tiems}30mm$, the collection efficiency induced by centrifugal force was represented as about 35% with inlet velocity 15 - 21m/s.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1689-1696
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• 2017

In recent academic and industrial circles of the Republic of Korea, the securement of available reactive power reserve against the line faults is at issue. Thus, simulations have been performed for the securing of effective reactive power reserve (effective Q) to prepare for the line faults and improve reactive power monitoring and control methods. That is, a research has been conducted for the fast-decoupled Newton-Raphson method. In this study, a method that distinguishes source and sink regions to carry out faster provision of information in the event of line fault has been proposed. This method can perform quantification with the formula that calculates voltage variations in the line flow. The line flow and voltage changes can be easily induced by the power flow calculation performed every second in the operation system. It is expected that the proposed method will be able to contribute to securement of power system stability by securing efficient reactive power. Also, the proposed method will be able to contribute to prepare against contingencies effectively. It is not easy to prepare quickly for the situation where voltage drops rapidly due to the exhaustion of reactive power source by observing voltage information only. This paper's simulation was performed on the large scale Korean power system in steady state.

• Journal of Power Electronics
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• v.16 no.1
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• pp.38-47
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• 2016

This paper presents DG based droop controlled parallel inverter systems with virtual impedance considering the unequal resistive-inductive combined line impedance condition. This causes a reactive power sharing error and dynamic performance degradation. Each of these drawbacks can be solved by adding the feedforward term of each line impedance voltage drop or injecting the virtual inductor. However, if the line impedances are high enough because of the long distance between the DG and the PCC or if the capacity of the system is large so that the output current is very large, this leads to a high virtual inductor voltage drop which causes reductions of the output voltage and power. Therefore, the line impedance voltage drops and the virtual inductor and resistor voltage drop compensation methods have been considered to solve these problems. The proposed method has been verified in comparison with the conventional droop method through PSIM simulation and low-scale experimental results.

• Journal of Electrical Engineering and Technology
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• v.5 no.1
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• pp.156-162
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• 2010

This paper describes electrical and optical characteristics of discharge developments in water under inhomogeneous fields caused by impulse voltages. Predischarge current and discharge light images were observed for different water resistivities and applied voltages between the hemispherical water tank and the needle electrode. The electrical parameters characterizing discharge developments are analyzed based on the discharge light images and voltage-current (V-I) curves, and electrical resistances derived by voltage and current waveforms. As a result, when the streamer corona is initiated at the tip of the needle electrode, the transient resistance suddenly drops and V-I curves form a 'loop'. The length of streamer propagation is increased with increasing peak value of the applied voltage, and the streamer corona extension is enlarged with increasing water resistivity. The electrical resistances before streamer corona initiation are rarely changed by different applied voltages. On the other hand, the electrical resistances after streamer corona initiation are found to be inversely proportional to the peak value of the applied voltage, and the decreasing rates for higher water resistivities are much higher than those for lower water resistivities. The time to streamer corona initiation and the time to the second current peak become shorter as the voltage increases. Finally, the calculated resistances after streamer corona initiation are almost the same trace of measured resistances, but they are smaller than the measured values.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.269-270
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• 2016

본 논문에서는 인버터의 정확한 전압 합성을 위해 인버터의 비선형성을 보상하는 기법을 제안한다. 인버터에서 데드타임, 스위칭 소자의 도통손실, 스위칭 지연 등의 성분들은 전압 합성에 비선형성을 유발한다. 제안된 방법은 이러한 요인들을 각 상별로 분석하고, 이를 보상함으로써 보다 정밀한 전압 합성을 가능케 한다. 이 방법의 유효성은 실험을 통하여 입증하였다.

• Journal of the Korean Ceramic Society
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• v.20 no.1
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• pp.31-36
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• 1983

The photoelectrochemical conversion by polycrystalline $TiO_2$ electrodes is effected by applied voltage oxidized $TiO_2$ thickness temperature and concentration of a, P. E. C cell. Anodic current starts at -0.8V in 1N-NaOH solu-tion and photocurrent appears around 420nm frequency. And the emf of the cell drops with the rate of 58.5mV/PH.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.723-727
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• 2004

A new high-performance and low cost single switch energy recovery display driver for an AC plasma display panel (PDP) is proposed. Since it is composed of only one auxiliary power switch, two small inductors, and eight diodes compared with the conventional circuit consisting of four auxiliary power switches, two small inductors, eight power diodes, and two external capacitors, it features a much simpler structure and lower cost. Nevertheless, since the rootmean-square (RMS) value of the inductor current is very small, it also has very desirable advantages such as n low conduction loss and high efficiency. Furthermore, there are no serious voltage-drops caused by the large gas-discharge current with the aid of the discharge current compensation, which can also greatly reduce the current flowing through power switches and maintain the panel to light at n lower sustaining voltage. In addition, all main power switches are turned on under the zero-voltage switching (ZVS) and thus, the proposed circuit has a improved EMI, increased reliability, and high efficiency. Therefore, the proposed circuit will be well suited to the wall hanging PDP TV. To confirm the validity of the proposed circuit, circuit operations, features,and design considerations are presented and verified experimentally on a 6-inch PDP, 50kHz-switching frequency, and sustaining voltage 141V based prototype.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.37-44
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• 2013

In this paper, the characteristics of portable fuel cell system are introduced and the dynamic response of output voltage of fuel cell stack with internal humidifier is analyzed. When the output of the fuel cell (FC) stack is short-circuited for humidification, the output voltage of the FC stack rapidly drops. In order to maintain the load voltage in the required range, dynamic compensation methods are proposed: 1) installing a capacitor behind the output of the FC stack; 2) utilizing the bi-directional converter. Especially, bi-directional converter is used when short of the FC output is detected or predicted by algorithm using data which is measured during previous three cycles. These methods are simulated by PSIM 9.0, then experimental results from the fuel cell system prototype verify the validity of the proposed methods.