• Journal of Power Electronics
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• 제17권4호
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• pp.1004-1013
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• 2017

This paper presents an interleaving scheme for parallel-connected power systems to reduce the DC-link current ripple. A paralleled generator system generates current ripple by the Pulse Width Modulation (PWM) of each generator side converter. The current ripple in the DC-link degrades the efficiency of the whole generator system and decreases the lifetime of the DC-link capacitors. To mitigate these issues, the expression of the DC-link current is derived by a double-integral Fourier analysis while considering the modulation schemes. Optimized interleaving angles for the parallel generator system are obtained based on an analysis to minimize the dominant current harmonics component. Finally, the proposed interleaving scheme reduces the RMS value of the DC-link current ripple. Simulation and experimental results verify the effectiveness of the proposed interleaving scheme.

• 한국의학물리학회지:의학물리
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• 제27권3호
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• pp.125-130
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• 2016

Dual energy computed tomography (DECT) is used to classify two materials and quantify the mass density of each material in the human body. An energy modulation filter based DECT could acquire two images, which are generated by the low- and high-energy photon spectra, in one scan, with one tube and detector. In the case of DECT using the energy modulation filter, the filter should perform the optimization process for the type of materials and thicknesses for generating two photon spectra. In this study, Geant4 Monte-Carlo simulation toolkit was used to execute the optimization process for determining the property of the energy modulation filter. In the process, various materials used for the energy modulation filter are copper (Cu, $8.96g/cm^3$), niobium (Nb, $8.57g/cm^3$), stannum (Sn, $7.31g/cm^3$), gold (Au, $19.32g/cm^3$), and lead (Pb, $11.34g/cm^3$). The thickness of the modulation filter varied from 0.1 mm to 1.0 mm. To evaluate the overlap region of the low- and high-energy spectrum, Geant4 Monte-Carlo simulation is used. The variation of the photon flux and the mean energy of photon spectrum that passes through the energy modulation filter are evaluated. In the primary photon spectrum of 80 kVp, the optimal modulation filter is a 0.1 mm lead filter that can acquire the same mean energy of 140 kVp photon spectrum. The lead filter of 0.1 mm based dual energy CBCT is required to increase the tube current 4.37 times than the original tube current owing to the 77.1% attenuation in the filter.

• 해양환경안전학회지
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• 제25권4호
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• pp.498-503
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• 2019

해양산업분야에서는 극심한 대기오염으로 인하여 전기추진선박에 대한 관심이 높아지고 있다. 이로 인해 선내 전력품질의 저하를 개선하기 위한 연구가 활발히 진행되고 있다. 기존 DFE 정류기의 입력전류 고조파 함유량을 완화시키기 위해 수동형필터, 노치필터, 능동형필터 등을 이용한 다양한 방법이 등장하였다. 그 중에서도 능동필터의 일종인 AFE(Active Front End) 정류장치가 우수한 기술로써 평가받고 있다. 본 논문에서는 공간벡터변조에 의한 AFE정류장치의 전류제어방식을 제안하였다. 기존의 히스테리시스 방식, 삼각파 변조방식 및 공간벡터변조방식을 PSIM을 사용해 시뮬레이션을 수행하여 비교, 분석하였고, 그 결과 공간벡터변조방식이 구조가 간단하고 성능이 가장 우수함을 확인하였다.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.83-86
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• 1999

We have fabricated $_2Cu_3O_7$ step-edge junctions with different step orientations and studied their transition properties. Steps with different orientations were prepared on the substrate. Josephson junctions were made on a single substrate with step orientations ranging from 0$^{\circ}$ to 165$^{\circ}$ at 15$^{\circ}$ interval. We measured current-voltage characteristics, the critical current, and the superconducting transition temperature as a function of the angle. The critical current showed a modulation that has a maximum near 0$^{\circ}$ or 90$^{\circ}$ and a minimum near 45$^{\circ}$ and 135$^{\circ}$. We believe that the critical current modulation with the step orientation could be associated with the symmetry of high T$_c$ superconductor.

• 한국콘텐츠학회논문지
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• 제7권1호
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• pp.116-123
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• 2007

본 논문은 OLED 패널 소스 구동회로에서 구동 전류의 크기와 폭을 조절하는 새로운 amplitude width modulation(AWM) 방식을 제안하였다. 기존의 소스 구동회로에서 pulse amplitude modulation(PAM) 방식은 DAC 회로 추가로 인해 크기가 커진다는 단점이 있고, pulse width modulation(PWM) 방식은 낮은 그레이 신호 레벨에서 발광 효율이 나쁜 단점이 있다. 이와 같은 단점을 개선하기 위해 본 논문에는 색상 데이터 비트의 MSB를 이용하여 구동 전류의 레벨을 제어하고, 데이터 비트의 LSB를 이용하여 구동 전류의 폭을 조정하는 구동방식을 제안하였다. 제안된 구동 방식은 $0.35-{\mu}m$ 3-poly 4-metal CMOS high voltage 공정을 사용하여 구현하였다. 시뮬레이션 결과는 제안된 AWM 구동 회로가 PAM 방식에 비해 회로 크기를 줄였고 신호 레벨이 낮은 영역에서 PAM과 거의 동일한 발광 효율을 얻었다.

• 대한전자공학회논문지
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• 제17권2호
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• pp.10-14
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• 1980

본 논문에서는 DH-laser diode의 threshold current를 계산하기 위하여 2차고조파 왜곡 (se cond harmonic distortion)에 대해 Rate 방정식 (Rate-equation)을 동적상태와 정적상태 방정식으로 연릴하여 계산하였다. 특히 고조파 왜곡 ( )을 계산하는데 바이어스 전류 에 대하여 변조 전류 을 변조계수 m으로 놓고 (Jm=mJo)계산하여 주입전류 J가 Jth에서 2차 고조파 왜곡이 최대치를 가짐을 보여 ,이제까지 알려진 Jth조사 방법보다 간편하고 정확하게 조사할 수 있음을 제시하였다.

• Journal of Power Electronics
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• 제1권2호
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• pp.71-77
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• 2001

This paper proposes a new zero-current switching (ZCS) pulse-width modulation (PWM) switch cell that has no additional conduction loss of the main switch. In this cell, the main switch and the auxiliary switch turn on and turn off under zero current condition. The diodes commutate softly and the reverse recovery problems are alleviated. The conduction loss and the current stress of the main switch are minimized, since the resonating current stress of the main switch are minimized, since the resonating current for the soft switching does not flow through the main switch. Based on the proposed ZCS PWM switch cell, a new family of DC to DC PWM converters is derived. The new family of ZCS PWM converters is suitable for the high power applications employing IGBTs. Among the new family of DC to DB PWM converters, a boost converter was taken as an example and has been analyzed. Design guidelines with a design example are described and verified by experimental results from the 2.5 kW prototype converter operating at 40 kHz.

• Journal of Power Electronics
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• 제10권2호
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• pp.146-154
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• 2010

In this paper two dual output current-type inverters are proposed. These inverters have been called a current source nines-witch inverter and a current-type z-source nine-switch inverter by the authors. The proposed inverters have two independent current source outputs. Compared to two independent current source inverters, the proposed converters are implemented with fewer semiconductor switches. Space vector modulation (SVM) is proposed for these converters. Simulation results show the validity and performance of the proposed inverters.

• 전력전자학회논문지
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• 제23권1호
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• pp.9-15
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• 2018

This study investigates a bidirectional quasi-Z-source inverter (Bq-ZSI) system with bidirectional power transfer capability and a modified space vector modulation scheme for reducing the ripple of the inductor current. By replacing the diode in the impedance network with an active switch, the power flow can be bidirectional. The average inductor current of the Bq-ZSI network is negative in the regenerative braking mode, thereby regenerating the power. In addition, modified space vector modulation scheme is applied to the Bq-ZSI to control shoot-through time effectively. A 5 kW prototype is built and tested to implement the proposed system. Experimental results show that the Bq-ZSI system is capable of regenerative braking of the induction motor and that the modified space vector modulation method is efficient.

• 대한전자공학회논문지SD
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• 제41권10호
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• pp.17-22
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• 2004

본 논문에서는 진폭 변조와 펄스 폭 변조를 모두 사용하는 새로운 AMOLED 디스플레이 구동 방식을 개발하였다. 펄스 폭 변조를 위해서 다섯 개의 서브 프레임으로 화상 프레임을 나누었고 진폭 변조를 위해 TFT 게이트 전압에 의해 제어되는 3가지의 OLED 휘도(전류) 레벨을 사용하였다. 이 두 종류의 변조를 조합하여 35(=243) 계조를 얻었다. 그리고 DAC를 사용하지 않고 2개의 쉬프트 레지스터를 갖는 새로운 데이터 전극 구동 회로를 설계하였다. 회로 동작은 6㎛ 채널 길이 다결정 TFT의 전류-전압 특성에서 추출된 TFT 파라미터를 이용한 HSpice 시뮬레이션을 통하여 검증하였다. 시뮬레이션 결과로부터 320×240, 이중 스캔, 243 계조 AMOLED 디스플레이를 구현할 수 있음을 확인하였다.