• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.10
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• pp.542-549
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• 2004

The conventional fault location algorithms based on the travelling waves have an inherent problem. In cases of the close-up faults occurring near the relaying point and of the faults having zero degree inception angle of voltage signals, the conventional algorithms can not estimate an accurate fault distance. It is because the shapes of travelling waves are near sinusoidal in those cases. A new method solving this problem is presented in this paper. An FIR(Finite Impulse response) filter which makes high frequency components prominent and makes the power frequency component and dc-offset attenuated is used. With this method, the cross-correlation peak is to be very clear when a close-up fault or a fault having near zero-degree inception angle occurs. The cross-correlation peaks can be clearly distinguished and accurate fault location is practically possible consequently. A series of simulation studies using EMTP(Electromagnetic Transients Program) show that the proposed algorithm can calculate an accurate fault distance having maximum 2% or less error.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.10
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• pp.1215-1221
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• 1999

A high speed digital distance relaying algorithm based on a Wavelet Transformation is proposed. To obtain stable phasor values very quickly, first, a lowpass filter which has low cutoff frequency is used. Secondly, db2(Daubechies 2) Wavelet which has the data window of 4 samples is used. A FIR filter which removes the DC-offset component in current relaying signals is applied. In accordance with a series of tests, the operation time of the relaying algorithm is less than 3/4 cycles after faults in a 80 [km], 154[kV], 60[Hz] over-head transmission line system.

• Proceedings of the IEEK Conference
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• 2000.11b
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• pp.9-12
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• 2000

InP/lnGaAs heterojunciton phototransistors (HPTs) with transparent emitter contacts were fabricated and characterized. Indium Tin Oxide was RF sputtered for the emitter contacts. By comparison with InP/InGaAs HBTs, the dc characteristics of InP/lnGaAs HPTs demonstrated offset voltage due to ITO emitter contacts and similar common emitter current gain. The model parameters were extracted and a simple SPICE simulations were performed.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.987-990
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• 2003

This paper presents a cross-coupled RF VCO with high-Q MEMS-based spiral inductors. Since the use of high-Q inductors is critical to VCO design, MEMS-based spiral inductors with the Q-factor of nearly 22 are used for the RF VCO with an active cascode current source. The RF VCO circuits including spiral inductors have been designed and simulated in GaAs MMIC-MEMS process. The simulation results of the VCO circuits showed the phase noise of -180dBc/Hz at an offset frequency of 500KHz. The RF VCO circuit simulatinon used 2mA DC current and 3.3V supply.

• Journal of Industrial Technology
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• v.21 no.A
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• pp.51-57
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• 2001

In this paper, a novel overmodulation strategy for space-rector PWM(SYPWM) inverters to utilize dc link voltage fully is presented. The proposed strategy uses the concept of SVPWM based on the zero sequence signal(offset voltage) injection principle. So, by modifying the pole voltage simply, the linear control of inverter output voltage over the whole overmodulation range can be achieved easily. The proposed strategy is so simple that its practical implementation is easy. The validity of the proposed strategy is confirmed by the experimental results.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.270-273
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• 2003

The design, fabrication, and measured result of a 4.7 GHz differential VCO (Voltage Controlled Oscillator) for a 5.2 GHz WLAN (Wireless Local Area Network) applications is presented. The circuit is designed in a 0.35 mm technology employing three metal layers. The design is based on a fully integrated LC tank using spiral inductors. Measured tuning range is 10% of oscillation frequency with a control voltage from 0 to 3.0 V. Oscillation power of $\square$ 2.3 dBm at 4.63 GHz is measured with 21 mA DC current at 3V supply. The phase noise is $\square$ 104.17 dBc/Hz at 1 MHz offset.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.547-548
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• 2015

In order to reduce error of the distance relay, we propose an improved fault locating scheme using DC offset removal filter. We were modeled 154 kV transmission system using ATP software in order to demonstrate the usefulness of proposed scheme, and applied to the proposed scheme using collected voltage signal and current signal by line-to-ground fault.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.25-27
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• 2006

This paper proposes a new full ZVS-range asymmetrical half bridge converter. It uses the variable transient current build-up technique with the load variations. The current build-up is accomplished by using the secondary synchronous switch control. Due to the blocking capacitor in secondary side, the voltage applied to leakage inductor varies with the load variations during current build-up period. Therefore, the unnecessary current build-up of leakage inductor current in heavy load condition is prevented and more current build-up in medium and light load condition is achieved for ZVS operation. That is, the variant current build-up with the load variation is accomplished for the ZVS operation. Furthermore, the DC offset of the transformer magnetizing current is also eliminated and the utilization of magnetic core is maximized.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.428-431
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• 2006

Matching transformer in Dynamic Voltage Compensator is needed for grid connection and isolation. Flux saturation in transformer will be occurred by voltage of transformer from inverter and DC offset voltage and flux saturation makes over current in transformer. In this paper, mathematical modeling of matching transformer is proposed for flux saturation simulation of Dynamic Voltage Compensator.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.447-454
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• 1998

This paper describes a modeling and current control techniques of Distribution static condenser (D-STATCON) for power factor compensation. The current control is based on the predictive and the space vector PWM scheme. The predictive current controlled PWM D-STATCON can maintain its performance with power factor compensation and fixed switching frequency. By using the space vector control low ripple and offset in the current and the voltage as well as fast dynamic responses are achieved with a small DC link capacitance employed.