• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.694-696
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• 2005

Although DC ground resistance is a good index of grounding performance for grounding electrodes, it does not reflect the grounding performance during transient state. Besides, impulse ground impedance, which is defined by a ratio of the peak value of transient ground potential rise to the peak value of impulse current, cannot be an absolute index due to its dependence on impulse current shape. In this paper, ground impedance characteristics of ground electrodes has been measured in frequency domain ranging from 1 Hz to hundreds of kHz. Equivalent circuit models and transfer function models of the ground rod have been identified from the measured values of ground impedance in frequency domain.

• 한국철도학회논문집
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• 제3권3호
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• pp.131-138
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• 2000

The design of current collection system of high speed train requires the fundamental understandings for the dynamic characteristics of catenary system and pantograph. The stiffness of catenary system of high speed train has the varying characteristics for the change of contact point with pantograph, since the supporting pole and hanger make the different boundary conditions for the up-down stiffness of a trolley wire. The variation of stiffness results in Mathiue equation, which characterizes the stability of the system. However, the two-term variation of the stiffness due to span length and hanger distance cannot be solved analytically. In this paper, the stiffness variations are calculated and the physical reasoning of linear model and one term Mathieu equation are reviewed. And the numerical analysis for the two-term variation of the stiffness is done for the several design parameters of pantograph.

• 전력전자학회논문지
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• 제6권2호
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• pp.180-190
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• 2001

본 논문에서는 브러시리스 직류 전동기(BLDCM)의 정류과정에서 발생하는 유도성 상 전류의 위상각 제어에 의한 토크 리플의 감소 방법에 대하여 연구한다. 고정자 코일에서 발생하는 유도성 전이 전류에 대한 위상지연의 크기는 전동기의 회전속도에 따라 달라지므로, 속도에 대한 보상각을 결정하고 테이블 처리에 의하여 실시간 제어한다. 실험으로, AVR 8515 마이크로 프로세서를 이용하여 위상지연을 보상하는 회로를 설계하였으며 4극 3상의 브러시리스 직류 전동기에 대하여 전동기의 모든 운전영역에서 토크 리플이 현저하게 감소함을 확인하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.493-497
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• 1998

In this paper, a three phase voltage source inverter synchronous motor drive is introduced which is capable of producing an approximate to sine-wave currents in the stator windings. Compare to a conventional current forced synchronous machine drive, for the same machine loss, a gain in out put per unit overall volume of 125% at a 50Hz supply frequency has been achieved. In addition, the torque pulsation has been drastically reduced. These improvements are achieved by introducing new rotor windings which are capable of controlling the stator current waveforms an approximate to sine-wave. A computer program has been developed which can be used to predict the dynamic performance of this drive/system. The paper describes the design of rotor windings for cylindrical rotor motor but the theory is equally applicable to salient-pole designs.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.324-328
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• 2001

This paper presents parallel operation and control loop design of ZVT(Zero Voltage Transition) Full Bridge DC/DC Converter. At parallel operation of ZVT Full Bridge Converter, dynamic current shared inductor devides the same current of unit converter and ZVT circuit and aids to high efficiency in the system. Base on the modeling of ZVT. Full Bridge Converter, the control loop is designed using a simple two-pole, one-zero compensation circuit. To show the validity of the design procedures, the small signal analysis of the closed loop system and open loop system is carried out and the superiority of the dynamic characteristics is verified through the experiment with a 2kW, 50kHz prototype converter.

• Transactions on Electrical and Electronic Materials
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• 제7권6호
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• pp.319-323
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• 2006

The problem of the partial discharge (PD) extinction is investigated. The transient process takes place in a small spherical inclusion which is located in the dielectric. Both the losses caused by polarization and ohmic losses as the dielectric parameters are taken into account. From the inclusion standpoint the dielectric is considered as an active two-pole element (equivalent generator) and inclusion represents by own current-voltage curve. PD extinction voltage was shown to depend on the polarization loss tangent.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2000년도 춘계학술대회 논문집
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• pp.598-605
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• 2000

The design of a current collection system of high speed train requires the fundamental understandings fer the dynamic characteristics of a catenary system and pantograph. The stiffness of the catenary system of high speed train has the varying characteristics for the change of the contact point with a pantograph, since the supporting pole and hanger make the different boundary conditions for the updown stiffness of a trolley wire. The variation of stiffness results in Mathiue equation, which characterizes the stability of the system. However, the two terms variation of the stiffness due to span length and hanger distance cannot be solved analytically. In this paper, the stiffness variations are calculated, and the physical reasoning of linear model and one term Mathieu equation are reviewed. And the numerical analysis for the two term variation of the stiffness is done for the several design parameters of the pantograph.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2000년도 International Symposium on Magnetics The 2000 Fall Conference
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• pp.381-388
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• 2000

By applying Current-applied Pressure-Assisted process, we could obtain full dense isotropic and anisotropic NdFeB magnets from rapidly quenched MQP-A powder. The Nd contents are found to play an important role during the CA-press and CA-deformation process. The (BH)$\sub$max/ of CA-pressed and CA-deformed magnets are 131 kJ/㎥(16.5 MGOe) and 352 kJ/㎥(44.2 MGOe), respectively. The texture of CA-deformed anisotropic NdFeB magnets with thickness reduction was investigated by pole figure, and the (006) texture was increase with the increase of thickness reduction. With the increment in thickness reduction from 50%, 60% to 80%, W$\sub$50/ decreases from 76$\^$$^{\circ}$/, 62.5$\^$$^{\circ}$/ to 17$\^$$^{\circ}$/, respectively.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2015년도 전력전자학술대회 논문집
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• pp.177-178
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• 2015

This paper presents a neutral point deviation compensating control algorithm applied to a 3-level NPC converter. The neutral point deviation is analyzed with a focus on the current flowing out of or into the neutral point of the dc link. Based on the zero sequence components of the reference voltages, this paper analyzes the neutral point deviation and balancing control for 3-level NPC converter. An analytical method is proposed to calculate the injected zero sequence voltage for NP balancing based on average neutral current. This paper also proposes a control scheme compensating for the neutral point deviation under generalized unbalanced grid operating conditions. The positive and negative sequence components of the pole voltages and ac input currents are employed to accurately explain the behavior of 3-level NPC converter. Simulation and experimental results for a test set up of 30kW are shown to verify the validity of the proposed algorithm.

• 한국전기전자재료학회논문지
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• 제32권3호
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• pp.234-240
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• 2019

In this work, the magnetic arc reduction phenomena encountered in AC relay contacts were analyzed. To this end, arc duration, instantaneous voltage, and current changes due to changes in the magnetic field were observed. The arc generated at the contact point was affected by the magnitude of the applied magnetic field; the voltage and current waveforms rapidly intersected, resulting in a decrease in arc duration and arc energy. Furthermore, the orientation of the N pole of the magnetic field was found to play a role in the effectiveness of potential arc prevention.