• Journal of Power Electronics
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• 제18권3호
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• pp.802-816
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• 2018

A digital direct phase-shift control (DDPSC) method based on the phase-shifted full-bridge LLC (PSFB-LLC) converter is presented. This work combines DDPSC with the conventional linear control to obtain a hybrid control strategy that has the advantages of linear control and DDPSC control. The strategy is easy to realize and has good dynamic responses. The PSFB-LLC circuit structure is simple and works in the fixed frequency mode, which is beneficial to magnetic component design; it can realize the ZVS of the switch and the ZCS of the rectifier diode in a wide load range. In this work, the PSFB-LLC converter resonator is analyzed in detail, and the concrete realization scheme of the hybrid control strategy is provided by analyzing the state-plane trajectory and the time-domain model. Finally, a 3 kW prototype is developed, and the feasibility and effectiveness of the DDPSC controller and the hybrid strategy are verified by experimental results.

• 한국초전도ㆍ저온공학회논문지
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• 제18권2호
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• pp.18-20
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• 2016

The study of superconducting fault current limiter (SFCL) is continuously being studied as a countermeasure for reducing fault-current in the power system. When the fault occurred in the power system, the fault-current was limited by the generated impedance of SFCLs. The operational characteristics of the flux-offset type SFCL according to turn ratios between the primary and the secondary winding of a reactor were compared in this study. We connected the secondary core to a superconductor and a SCR switch in series in the suggested structure. The fault current in the primary and the secondary winding of the reactor and the voltage of the superconductor on the secondary were measured and compared. The results showed that the fault current in the load line was the lowest and the voltage applied at both ends of the superconductor was also low when the secondary winding of the reactor had lower turn ratio than the primary. It was confirmed based on these results that the turn ratio of the secondary winding of the reactor must be designed to be lower than that of the primary winding to reduce the burden of the superconductor and to lower the fault current. Also, the suggested structure could increase the duration of the limited current by limiting the continuous current after the first half cycle from the fault with the fault current limiter.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권3호
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• pp.372-378
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• 2012

This paper deals with a 3-phase voltage disturbance generator for a performance test of custom power devices such as dynamic voltage restorers (DVR), dynamic uninterruptable power supplies (UPS), etc. The operating principle of the proposed circuit is described in each mode of voltage sag, swell, outage, and unbalance. The main components of the proposed disturbance generator are silicone controlled rectifier (SCR) thyristors, variable autotransformers, and transformers. Therefore, the disturbance generator can be implemented with a considerably low cost compared to the conventional pulse width modified (PWM) inverter and converter type generators. Furthermore, it has good features of high reliability with simple structure, high efficiency caused by no PWM switching of the SCR thyristors, and easy control with a wide variation range. To verify the validity of the proposed scheme, simulations and experiments are carried out.

• 조명전기설비학회논문지
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• 제15권2호
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• pp.73-79
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• 2001

본 논문은 심플한 단상 에어컨의 역률 개선회로에 관해 설명한다. 정류기에 역률제어회로를 적용함에 의해서 전원선으로의 고조파 삽입을 줄일 수 있고, 효율을 향상시킬 수 있으며, 기존의 인버터와 비교해서 전체 시스템 가격을 낮출 수 있다. 또한 역률제어회로의 출력전압을 안정화함에 의해서 시스템 성능을 향상시킨다. 다이오드 정류기의 전류 파형을 향상시키기 위해 전압 다이오드 정류기에 대한 새로운 원리를 제안한다. 제안한 회로의 설계방법은 시뮬레이션과 실험에 의해 확인하였다. 그리고 기존의 펄스폭변조 인버터와 반펄스폭변조 인버터를 비교하였으며, 제안된 HPWM 인버터에 의해서 낮은 스위칭 손실과 오버슈팅을 제어할 수 있다.

• 조명전기설비학회논문지
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• 제27권3호
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• pp.55-64
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• 2013

In this paper, a new topology which can add a small reactor in series to a condenser-bank type reactive power compensator to limit current is proposed. And also the proposed topology can add or remove a power condenser safely without any addition of inrush-current suppression resistance. The proposed method tests variable resistance of the drain source of a switching device which is controlled by gate voltage in a two-way switch with a diode rectifier and FET switch. In other words, the proposed method is a inrush-current suppression method with the structure of variable resistance. In particular, the proposed method creates smooth current without any resonance in inrush-current as well as is not limited by the time of switch on and off.

• Journal of Power Electronics
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• 제15권2호
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• pp.309-318
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• 2015

This study proposes a dual-output single-stage bridgeless single-ended primary-inductor converter (DOSSBS) that can completely remove the front-end full-bridge alternating current-direct current rectifier to accomplish power factor correction for universal line input. Without the need for bridge diodes, the proposed converter has the advantages of low component count and simple structure, and can thus significantly reduce power loss. DOSSBS has two uncommon output ports to provide different voltage levels to loads, instead of using two separate power factor correctors or multi-stage configurations in a single stage. Therefore, this proposed converter is cost-effective and compact. A magnetically coupled inductor is introduced in DOSSBS to replace two separate inductors to decrease volume and cost. Energy stored in the leakage inductance of the coupled inductor can be completely recycled. In each line cycle, the two active switches in DOSSBS are operated in either high-frequency pulse-width modulation pattern or low-frequency rectifying mode for switching loss reduction. A prototype for dealing with an $85-265V_{rms}$ universal line is designed, analyzed, and built. Practical measurements demonstrate the feasibility and functionality of the proposed converter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.1480-1482
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• 2005

The major causes of power quality deterioration are harmonic current through semiconductor switching device, due to use of nonlinear loads such as diodes rectifier or thyristor rectifiers. In response to this concerns, this paper presents a new control method of single-phase active power filter(APF) for the compensation of harmonic current components in nonlinear loads. In order to make the complex calculation to be possible, the single-phase system that has two phases was made by constructing a imaginary second-phase giving time delay to load currents. In the conventional method, a imaginary-phase lagged to the load current T/4(here T is the fundamental cycle) was made. But in this proposed method, the new signal, which has the delayed phase through the filter, using the phase-delay property of low-pass filter, was used as the second phase. As this control method is applied to the system of single phase, an instantaneous calculation was done rather by using the rotating reference frames that synchronizes with source-frequency than by applying instantaneous reactive power theory that uses the conventional fixed reference frames.

• 전력전자학회논문지
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• 제26권2호
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• pp.112-119
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• 2021

This study proposes a design method of high-power-density and high-efficiency low-voltage DC-DC converters using SiC MOSFET and the optimized planar transformer design procedure based on the figure-of-merit. The secondary rectifying circuit of the phase-shifted full-bridge converter is compared to achieve high power density and high efficiency, and the phase-shifted full bridge converter with a current-doubler rectifier is selected. The planar transformer is designed by the proposed optimized design procedure and verified by FEA simulation. To validate the proposed design method, experimental results from a 3 kW prototype are provided. The prototype achieved 95.28% maximum efficiency and a power density of 2.98 kW/L.

• 한국철도학회논문집
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• 제19권6호
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• pp.727-735
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• 2016

철도차량용 구동 시스템의 주 변압기를 지능형 변압기로 대체하는 것은 철도차량의 효율을 높이기 위한 효과적인 방법이다. 지능형 변압기는 고전압 입력단을 저전압 직류단으로 변환하는 정류단 모듈과, 변환된 복수의 저전압 직류단 전압을 직/병렬로 연결하여 저전압 직류 출력 전압을 제어하는 Dual Active Bridge (DAB) 컨버터 모듈로 구성된다. DAB 컨버터는 고주파 변압기를 사이에 두고 양 측 Full-Bridge 컨버터의 전압 합성 방법에 따라 전력이 양방향으로 전달될 수 있다. 이 때, 양 측 Full-Bridge 컨버터의 전압 합성 방법에 따라 고주파 변압기로 흐르는 전류의 형태가 달라지게 되며, 이는 효율에 직접적인 영향을 미치게 된다. 본 논문은 중/저 전력 조건에서 DAB 컨버터의 효율을 개선하기 위한 새로운 modulation 방법을 제안한다. 제안하는 modulation 방법은 DAB 컨버터 내에 발생할 수 있는 무효 전력을 0으로 제어하도록 하며, 출력단 컨버터를 다이오드 정류기와 유사한 동작을 하도록 함으로써, 스위칭 손실을 최소화하도록 하였다. 제안된 modulation 방법을 통한 손실 저감은 900Vdc의 직류단 전압을 갖는 DAB 컨버터에 대한 시뮬레이션 결과를 통해 검증하였다.

• 한국철도학회논문집
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• 제19권5호
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• pp.617-628
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• 2016

본 논문은 철도차량의 추진용 유입식 변압기 및 AC/DC 컨버터를 대체하기 위한 지능형 변압기의 구조를 제안한다. 제안된 지능형 변압기는 반도체 스위칭 소자 및 고주파 변압기를 사용한 양방향 전력 변환 컨버터의 형태로써, 기존 변압기에 비해 경량화 되고, 역률 제어 등의 능동적인 제어 성능으로 인해 단상 계통 전원의 효율적인 활용을 가능하게 한다. 제안하는 지능형 변압기는 60Hz 교류 고전압을 직류 고전압으로 변환하기 위한 정류단으로 Neutral point clamped type 의 H-bridge 컨버터를 여러 개 직렬 연결해 구성했다. 직류로 변환된 입력단 전력은 고주파 변압기와 Neutral point clamped type H-bridge 컨버터 2개로 구성된 Dual-Active-Bridge 컨버터를 이용해 출력측에 필요한 저전압을 공급할 수 있도록 했다. 또한, 본 논문에서는 다수의 컨버터 모듈 내부 직류단 전압을 균형제어하며, 단상 교류 전원에서 직류 출력 전원간의 양방향 전력 제어를 가능하게 하는 제어 알고리즘을 제안한다. 제안한 지능형 변압기의 구조 및 제어 시스템은 75kVA 급 3.3kVrms 입력, 750VDC 출력의 지능형 변압기를 설계 및 회로 시뮬레이션 결과를 통해 검증했다.