• Journal of Electrical Engineering and Technology
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• 제3권3호
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• pp.391-400
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• 2008

Multi-pulse topology of converters using elementary six-pulse GTO - VSC (gate turn off based voltage source converter) operated under fundamental frequency switching (FFS) control is widely adopted in high power rating static synchronous compensators (STATCOM). Practically, a 48-pulse ($6{\times}8$ pulse) configuration is used with the phase angle control algorithm employing proportional and integral (PI) control methodology. These kinds of controllers, for example the ${\pm}80MVAR$ compensator at Inuyama switching station, KEPCO, Japan, employs two stages of magnetics viz. intermediate transformers (as many as VSCs) and a main coupling transformer to minimize harmonics distortion in the line and to achieve a desired operational efficiency. The magnetic circuit needs altogether nine transformers of which eight are phase shifting transformers (PST) used in the intermediate stage, each rating equal to or more than one eighth of the compensator rating, and the other one is the main coupling transformer having a power rating equal to that of the compensator. In this paper, a two-level 48-pulse ${\pm}100MVAR$ STATCOM is proposed where eight, six-pulse GTO-VSC are employed and magnetics is simplified to single-stage using four transformers of which three are PSTs and the other is a normal transformer. Thus, it reduces the magnetics to half of the value needed in the commercially available compensator. By adopting the simple PI-controllers, the model is simulated in a MATLAB environment by SimPowerSystems toolbox for voltage regulation in the transmission system. The simulation results show that the THD levels in line voltage and current are well below the limiting values specified in the IEEE Std 519-1992 for harmonic control in electrical power systems. The controller performance is observed reasonably well during capacitive and inductive modes of operation.

• 전력전자학회논문지
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• 제14권3호
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• pp.243-250
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• 2009

본 논문은 조명용 LED 구동 장치를 위한 새로운 방식의 Two-stage LED 구동 회로를 제안한다. 제안된 회로는 PFC flyback 회로의 다중 출력을 이용하여 LED 양단에 전압을 인가하여 LED 구동 회로의 출력 전압을 획기적으로 낮출 수 있어 LED 구동 회로에 사용되는 반도체 소자의 전압 스트레스를 크게 줄일 수 있다. 제안된 회로는Universal input에서 25 [W] 이상 조명 장치에 적용되는 IEC 61000-3-2 class C 규제를 만족하고, PWM 디밍을 사용하여 넓은 범위의 휘도 조절이 가능하다. 본 논문에서는 제안 회로의 동작 원리를 설명하고, 시뮬레이션 및 LED에 실제 적용 실험하여 제안 회로의 유용성을 입증하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.928-929
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• 2008

A dc/dc power conversion system using multi stage capacitor is proposed in this paper. The proposed new type converter is designed from high efficiency dc/dc converter with fixed boost ratio and variable voltage converter. The tests have been done using PSIM computer simulation to confirm the analysis and control concept.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 기술교육위원회 창립총회 및 학술대회 의료기기전시회
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• pp.19-22
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• 2001

For stabilization and improving power factor in the power lines, various Static Var Compensators(SVC) have been considered to be installed and partly applicated already. With all these merits of the SVC, it stil has demerits, principally evoking harmonic problems. So far, many harmonic reduction type inverters have been used in various parts. In this paper, the reactive power is controlled by amplitude of the output voltage. This paper propose that the multiple voltage source inverter have controllable power factor made by load vary at receive-stage as lagging and leakage control. The theoretical analysis on this system was confirmed through the computer simulation and the experiments.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 A
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• pp.403-406
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• 1995

In general, the reactive power is controlled by amplitude of the output voltage. This paper propose that the multiple voltage source inverter have controllable power factor made by load vary at receive-stage as lagging and leakage control.

• 한국정밀공학회지
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• 제21권6호
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• pp.167-171
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• 2004

In this paper, we proposed a new method to control the length of carbon nanotube using electrochemical etching. We made a nano probe that was composed of the tungsten tip and multi-wall carbon nanotube. The nano probe was placed on the nano stage and the carbon nanotube on the nano probe was etched in the electrolyte solution with the applied voltage. The overall procedures were done under optical microscope and can be monitored. We can obtain a nano probe with proper length through this procedure.

• Journal of Power Electronics
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• 제14권6호
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• pp.1166-1177
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• 2014

A new type of topology with medium-frequency-transformer (MFT) isolation for medium voltage wind power generation systems is proposed in this paper. This type of converter is a high density power conversion system, with high performance features suitable for next generation wind power systems in either on-shore or off-shore applications. The proposed topology employs single-phase cascaded multi-level AC-AC converters on the grid side and three phase matrix converters on the generator side, which are interfaced by medium frequency transformers. This avoids DC-Link electrolytic capacitors and/or resonant L-C components in the power flow path thereby improving the power density and system reliability. Several configurations are given to fit different applications. The modulation and control strategy has been detailed. As two important part of the whole system, a novel single phase AC-AC converter topology with its reliable six-step switching technique and a novel symmetrical 11-segment modulation strategy for two stage matrix converter (TSMC) is proposed at the special situation of medium frequency chopping. The validity of the proposed concept has been verified by simulation results and experiment waveforms from a scaled down laboratory prototype.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.395-399
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• 1996

The Clamp Mode(CM) Forward Zero Voltage Switching Multi Resonant Converter(ZVS-MRC) with self-driven synchronous rectifier in studied. The loss at the synchronous rectification stage of the converter is analyzed using MOSFET linear model and is compared with the loss at the conventional schottky diode rectification stage of the converter. From the results of the analysis, it is known that the use of MOSFETs as a synchronous rectifier reduces the loss at the rectification stage over the whole load range comparing the use of schottky diodes as a conventional rectifier in the converter. In order to verify the validity of the analysis, we have built a 33W(3.3V/10A) CM Forward ZVS-MRC with self-driven synchronous rectifier, in which switching frequency is 1MHz, and tested. From the experimental results, it is known that the synchronous rectification achieved about 1W improvement in the loss at the rectification stage and about 3% in the efficiency at the converter as compared with the conventional schottky diode rectification.

• 전력전자학회논문지
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• 제4권4호
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• pp.384-394
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• 1999

This paper deals with a fixed frequency full-bridge inverter type DC-DC high-power converter with high frequency high voltage(HFHV) transformer-coupled stage, which operates under quasi-resonant ZVS transition priciple in spite of a wide PWM-based voltage regulation processing and largely-changed load conditions. This multi-resonant(MR) converter topology is composed of a series capacitor-connected parallel resonant tank which makes the most of parasitic circuit reactive components of HFHV transformer and two additional quasi-resonant pole circuits incorporated into the bridge legs. The soft-switching operation and practical efficacy of this new converter circuit using the latest IGBTs are actually ascertained through 50kV trially-produced converter system operating using 20kHz/30kHz high voltage(HV) transformers which is applied for driving the diagnostic HV X-ray tube load in medical equipments. It is proved from a practical point of view that the switching losses of IGBTs and their electrical dynamic stresses relating to EMI noise can be considerably reduced under a high frequency(HF) switching-based phase-shift PWM control process for a load setting requirements.

• 한국안전학회지
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• 제11권2호
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• pp.150-159
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• 1996

본 연구에서는 하부구조적 결함을 갖는 전력계통의 정태 안전성 평가를 고려한 무효전력 제어 문제를 해결하기 위하여 A-team(Asynchronous team) 이론을 이용한 접근법을 제시한다. QVC는 무효전력 발전량, 전압치, 선로조류 및 다른 무효전력장치에 대한 제약조건하에서 최적의 전압을 유지하는 문제로써, 해의 정확도를 크게 해치지 않는 범위내에서 혼합정수계획법(MILP) 문제로 수식화 하였다. 안전성 평가는 계통의 모니터링을 통하여 얻어진 현재의 자료를 평가하여 상대적 강인성을 추정하는 것으로 교류 전력조류법에 기반을 둔 결정론적인 방법에 의해 계통안전성, 특히 전압안전성을 평가하였으며, 이진치 대신에 다수의 이산치를 제공하는 안전성 계량을 사용하였다. 계통의 효율적 운전을 목적으로 위의 두 문제를 통합하여 풀 수 있도록 A-team으로 명명된 새로운 조직기법을 도입하였다. A-team은 자치적(autonomous)이고, 병렬적으로(in parallel) 동작하고, 비동기적으로(asynchronously) 정보교환을 하는 agent들을 위 한 일종의 조직법으로 다수의 프로그램 (computer-based multi agent)을 이 용한 운용시스템의 구성에 적합한 방법으로 알려져 있다. 이 A-team을 이용한 방법은 실계통에 적용하기 위한 초기단계에 머무르고 있으나 대형계통의 여러 복잡한 문제를 해결할 수 있는 가능성을 갖고 있다.