• 전기학회논문지
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• 제58권10호
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• pp.1849-1854
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• 2009

This paper describes the design, evaluation and implementation of a compensating algorithm for an iron-cored measurement current transformer (CT) that removes the effects of the hysteresis characteristics of the iron-core. The exciting current resulting from the hysteresis characteristics of the core causes an error of the CT. The proposed algorithm decomposes the exciting current into the core loss current and the magnetizing current and each of them is estimated. The core loss current is calculated from the secondary voltage and the voltage-core loss current curve. The core flux linkage is calculated and then inserted into the flux-magnetizing current curve to estimate the magnetizing current. The exciting current at every sampling interval is obtained by summing the core loss and magnetizing currents and then added to the measured current to obtain the correct secondary current. The voltage-core loss current curve and flux-magnetizing current curves, which are different from the conventional curves, are derived in this paper. The performance of the proposed algorithm is validated under various conditions using EMTP generated data. The experimental test results of an iron-core type electronic CT, which consists of the iron-core and the compensation board, are also included. The results indicate that the proposed algorithm can improve the accuracy of the measurement CT significantly, and thus reduce the size and the cost of the CT.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 B
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• pp.723-725
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• 2003

The result of design and Partial fabrication of a 1 MVA single phase high temperature superconducting(HTS) transformer for power distributions are presented in this paper. The HTS windings are wound as double pancake windings which have advantages of uniform distribution of high voltage over the windings. the rated primary and secondary voltages are 22.9 kV and 6.6 kV respectively. Four HTS tapes are wound in parallel for secondary windings considering the rated currents of the transformer. The HTS windings will be cooled down to 65 K by natural convection of sub-cooled liquid nitrogen using a single-staged GM-cryocooler in order to make the stability of the HTS windings better. The iron core is designed as shell type and isolated from the liquid nitrogen by an FRP cryostat which have a room temperature bore. After the complete fabrication of the total HTS transformer system, performance test of the transformer will be carried out.

• 조명전기설비학회논문지
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• 제13권3호
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• pp.129-139
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• 1999

본 논문에서는 배전용변압기의 원격감시용 시스템 구축 및 운영기술을 제시하였다. 특히 이 시스템에서 사용하는 통신매체로서는 전력회사의 주요 배전선에 시설되어있는 CATV전송망을 활용하였다. 이 시스템은 배전용 변압기 2차전압, 전류를 측정하는 센서부분, 데이터의 부호와 및 해독을 담당하는 RF모뎀부분, 데이터를 송·수신하는 통신 매체부분, 그리고 모니터링된 계측데이터를 변화하는 서버부분 등 4개 주요요소로 구성되어 있다. 또 한 각 요소의 구성에 대한 기능과 개발과정을 기술하였으며, 중부지점의 실계통에 적용함으로써 본 논문에서는 제안한 시스템의 신뢰성과 효과성을 검증하였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2004년도 전력전자학술대회 논문집(1)
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• pp.341-345
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• 2004

A high efficiency and low device stress voltage and current clamping BVS PWM asymmetrical half bridge converter is proposed in this paper. To achieve the ZVS of power switches along the wide load range, the transformer leakage inductor $L_{Ikg}$ is increased. Then, to solve the problem related to ringing in the secondary rectifier caused by the resonance between $L_{Ikg}$ and rectifier junction capacitors, the proposed converter employs a voltage and current clamping cell, which helps voltages and currents of rectifier diodes to be clamped at the output voltage and output current, respectively. Therefore, no RC-snubber for rectifier diodes is needed and a high efficiency as well as low noise output voltage can be realized. In addition, since all energy stored in $L_{Ikg}$ is transferred to the output side, the circulating energy problem can be effectively solved and duty loss does net exist. The operational principle, theoretical analysis, and design considerations are presented. To confirm the operation, validity, and features of the proposed circuit, experimental results from a 425W, 385-170Vdc prototype are presented.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 Vol.19
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• pp.186-187
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• 2006

The development of SFCL (Superconducting Fault Current Limiter) is getting more important as the power demand is increased rapidly. Up to now, several kinds of SFCL have been proposed and it is expected that they will be applied to appropriate position considering their own properties. Amongst those proposed SFCL, flux-lock type SFCL using the magnetic cancelation for current limiting has the advantages of overcoming the technical difficulties that other types of SFCLs have. In this paper, the integrated three-phase flux-lock type SFCL was fabricated and its operational modes were investigated through the short circuit tests. The operational mode were to divided into four mode according to the variation of the currents flowing into the secondary winding connected the superconducting elements and the speed of the quench generation. It was expected that the improvement of current limiting characteristics of the SFCL could be possible through control of the operational mode.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
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• pp.708-713
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• 1994

A new flux observer based vector control system of an induction motor is constructed by using an observer in which the commanded stator currents are used to estimate the rotor flux. In this system, the flux observer is formulated by using a model of induction motor in a stationary coordinate system. By considering an observer of induction motor in a fixed co-ordinate system located on its secondary flux, a slip frequency controlled type of vector control system is also proposed. From these control schemes, the relation between the conventional slip frequency controlled type system and the observer based one is clarified. The steady-state error of the developed torque which is caused by the parameter change of induction motor is analyzed and discussed for the selection of observer gains. The poles of the observer error dynamics and those of the observer based vector control system are calculated analytically by neglecting the machine parameter change. In order to analyze the robust stability, a linear model of the observer based vector control system is proposed taking into account the machine parameter change. By using this model, the trajectories of the poles and zeros of the torque transfer function are computed and discussed. To test validity of the theoretical analysis, experiments are conducted by using a digital signal processor (TMS320C30) and a current controlled voltage source PWM inverter.

• 전력전자학회논문지
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• 제13권3호
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• pp.229-236
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• 2008

최근 중대용량의 교류전동기 구동에 다단 H-브릿지 인버터의 적용이 늘어나고 있다. 이 인버터의 주된 장점 중의 하나는 입력전류에 고조파성분이 적다는 것으로 이는 2차측이 다중의 위상이동 권선으로 이루어진 변압기를 사용함으로써 이루어진다. 본 논문은 다단 H-브릿지 인버터에 적용되는 위상이동 변압기의 권선 설계의 기본 방안과 입력전류 고조파의 이론적인 해석을 제시하고 있다. I부에서는 먼저 위상이동변압기의 입출력 전압관계식을 유도하고 위상이동과 변압기 설계와의 관련성에 대하여 서술하고 있다.

• 전력전자학회논문지
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• 제13권3호
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• pp.237-245
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• 2008

최근 중대용량의 교류전동기 구동에 다단 H-브릿지 인버터의 적용이 늘어나고 있다. 이 인버터의 주된 장점 중의 하나는 입력전류에 고조파성분이 적다는 것으로 이는 2차측이 다중의 위상이동 권선으로 이루어진 변압기를 사용함으로써 이루어진다. 본 논문은 다단 H-브릿지 인버터에 적용되는 위상이동 변압기의 권선 설계의 기본 방안과 입력전류 고조파의 이론적인 해석을 제시하고 있다. 위상이동 변압기를 다룬 I부에 이어 II부에서는 입력 선전류의 고조파 특성을 해석함으로써 고조파 제거를 위한 등간격 위상차 설정방식의 이론적 근거를 규명하였다.

• Journal of Electrical Engineering and Technology
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• 제11권3호
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• pp.675-682
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• 2016

Sudden voltage drops and outages frequently disturb the operation of sensitive loads for domestic, commercial, and industrial use. In some cases, these events may even impair the functioning of relevant equipment. To maintain power under such conditions, a UPS system is usually installed. Once a disturbance happens at the grid side, the line-interactive UPS system takes over the load to prevent an interruption. But, due to magnetic saturation of the transformer, a significant inrush current may occur for the transformer-coupled loads during this transition. The generation of such transient currents may in turn decrease the line voltage and activates over-current protecting devices of the system. In this work, a cost-effective, line-interactive UPS system is proposed that eliminates the inrush current phenomenon associated with transformer-coupled loads. The strategy was implemented by connecting a standard current-regulated voltage source inverter (CRVSI) to the secondary winding of the load transformer. During any transient condition at the grid side, the load current is monitored and regulated to achieve either seamless compensation of the load current or complete transferal of load from grid to the inverter. Experimental results were obtained for a prototype under all possible operating conditions so as to validate the performance of the proposed topology.

• 대한자원환경지질학회:학술대회논문집
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• 대한자원환경지질학회 1999년도 춘계 공동학술발표회
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• pp.90-93
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• 1999

We present a high frequency electromagnetic (EM) inversion scheme for detecting and characterizing a fracture using single-hole data. At high frequencies, say above tens of mega-hertz, since displacement currents cannot be ignored, electrical permittivity as well as electrical conductivity is to be considered together for analyzing the EM scattering data. In this paper, we have developed a three-step inversion scheme to map the fracture and to evaluate its electrical conductivity and permittivity. We performed EM profiling along the z-axis using three-component receivers for each source. The model was excited by a vertical magnetic dipole and the resistant magnetic fields were inverted using the non-linear least-squares method. Background resistivity and permittivity were easily obtained using vertical magnetic fields below 1 MHz and above 10 MHz, respectively. Both the vertical and dipping sheets were successfully mapped using the phase difference between 40 and 41 MHz. The electrical property of the sheet was well resolved using the information obtained in the previous two steps and secondary magnetic fields. Our study shows the potential of imaging the fracture in single-hole survey environment using the high frequency EM method.