• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.459-461
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• 1991

This paper proposes a novel AC voltage regulator topology. The output voltage is varied by controlling voltage drop of the transformer which is connected with load in series. The waveform of output voltage is clamped sinusoidal, then harmonic components are remarkably decreased compared with conventional phase control method. The feasibility of proposed topology is verified experimentally.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.379-381
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• 1994

This paper is concerned with a zero-voltage soft-switching PWM DC-DC high-pelter converter using IGBTs, which Bakes the most of the parastic LC parameters of high-voltage transformer link, for diagnostic X-Ray power generator. The converter circuit basically utilizes phase-shift pulse width modulated series resonant full-bridge PWM DC-DC high-Power converter operating at a constant frequency:20kHz. This technique brings about dramatic decreases in the switching losses of power devices and their electrical stresses as compared with the commonly-used hard-switching PWM DC-DC power converter. The high-frequency switching operation of the converters has some effective advantages, which consist in the physical reduction in size and weight and lowered acoustic noise.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.385-388
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• 1994

This paper presents a new configure rectifier which has improved input power factor and efficiency for DC arc weldings. Two rectifiers are series connected and they are single-phase full-wave phase controlled rectifiers that use a transformer with two center-tapped secondary. The input power factor can be improved by controlling the each phase of rectifiers sequentially, and then the efficiency can be also improved because the reactive component currents will be reduced. It is confirmed that the proposed rectifiers has about 80% of input power factor and efficiency with the experimental results which are carried out at the output ranges of 100A to 300A.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.432-434
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• 1994

This paper describes a phase-shifter which can flexibly adjust the active and reactive power flow through an ac transmission line. The phase-shifter has two voltage-source converters sharing an energy storage capacitor. The magnitude of the injected voltage is controlled by the converter I connected in parallel with the sending terminal, while that of phase angle by the converter II in series with the line through the coupling transformer. In order to analyze the whole system operation, an equivalent circuit model was developed and verified by a computer simulation with EMTP code.

• Proceedings of the KIEE Conference
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• 2007.11b
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• pp.87-88
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• 2007

We investigated the current limiting characteristics of flux-lock type superconducting fault current limiter using YBCO films University, Gwangju health college. The flux-lock type SFCL consisted of the transformer with a primary winding and a secondary winding connected in parallel, and the superconducting element was connected with secondary winding in series or parallel. Serial and parallel connections of superconducting elements are necessary for the increase of voltage and current capacities when we intend to apply the flux-lock type SFCL.

• Journal of Electrical Engineering and Technology
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• v.6 no.4
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• pp.459-465
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• 2011

A phasor estimation algorithm based on the least square curve fitting technique for the distorted secondary current due to current transformer (CT) saturation is proposed. The mathematical form of the secondary current during CT saturation is represented as the scaled primary current with magnetizing current. The information on the scaled primary current is estimated using the least square technique, with the measured secondary current in the saturated section. The proposed method can estimate the phasor of a fundamental frequency component during the saturated period. The performance of the algorithm is validated under various fault and CT conditions using a C400 CT model. A series of performance evaluations shows that the proposed phasor estimation algorithm can estimate the phasor of the fundamental frequency component with high accuracy, regardless of fault conditions and CT characteristics.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.11a
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• pp.287-292
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• 2004

The increasing use of nonlinear loads has resulted in an increase in the harmonic content of the load current for power transformers. Transformers subject to harmonic currents have higher losses and need to be derated. This paper presents a simple method for determining the capability of transformers to supply harmonic load currents and shows that the application of capacitor banks with a series connected reactor and harmonic filters will geatly increase the capability of transformers. The EDSA program was used as a simulation tool for the carse study.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.29-32
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• 2003

The UWB UHF coupler for GIS PD detection needs a balun(balance to unbalance transformer) to show its inherent UWB characteristics. In order to reduce the size of the balun and to make it practical in the conventional GIS, a novel tapered coaxial balun with a dielectric was proposed for the UWB UEIF coupler. The performance of the proposed balun was verified through a series of simulations, measurement and experiments. As results, both the conventional balun and the proposed balun of which length is one third of that of the conventional one showed good S11 characteristics, whereas the efficiency of the proposed balun increased as much as about 30% in comparison with the conventional one.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.965_966
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• 2009

In this paper, a new soft-switching Two-switch Forward converter topology has been proposed. Compared with conventional two-switch forward converter, the proposed converter employs an auxiliary switch and a clamp capacitor to instead of two reset diodes, not only its duty cycle can exceed 0.5 to achieve wide range input voltage, but also soft switching can be achieved for all switches. Especially, voltage stress across main switches can be clamped at $1/2V_{in}$, voltage stress across auxiliary switch can be clamped at $V_{in}$. In addition, due to clamp capacitor series with the transformer, duty ratio can be extended with equation $V_o=\frac{V_{in}(1-D}D{N}$. Therefore, as a kind of better cost-effective approach, it is very attractive for high input, wide range and high efficiency application.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.12
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• pp.80-86
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• 2012

The high-voltage pulse generator is consist of transformers of fundamental wave and harmonic waves, and shunt capacitances. The pulse has the fundamental wave and the harmonic waves that have been increased as a series circuit by the transformers to make high voltage pulse. This paper shows the high-voltage pulse generator simulation using a circuit program with experiment data. In the equivalent circuit, magnetized inductances and loss resistances which affect output voltage, have been obtained. The output capacitor circuits have characteristics of band pass. The output voltages of the pulse width 50% and 25%(PWM) were obtained. The output of the high-voltage pulse generator is 2.5kHz, 1.8kV.