• 전력전자학회논문지
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• 제22권4호
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• pp.345-352
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• 2017

In this paper, a non-dissipative snubber for reducing the switching losses in the step down converter is proposed. The conventional step down converter, e.g., buck converter, suffers from serious switching losses and consequentially heat generation because of its hard switching. Thus, it is unsuitable for high switching frequency operation. Reduction of the reactive components' size, such as an output inductor and capacitor, is difficult. The proposed snubber can slow down the increasing current slopes and switch voltage at turn-on and turn-off transients, thereby significantly reducing the switching loses. Additionally, the slowly increasing current during switch turn-on transition, can effectively solve the output rectifier diode reverse recovery problem. Therefore, the proposed non-dissipative snubber not only leads to the efficiency of converter operation at high switching frequency but also reduces the reactive components size in proportion to the switching frequency. To confirm the validity of the proposed circuit, theoretical analysis and experimental results from a 150 W, 1 MHz prototype are presented.

• 전력전자학회논문지
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• 제22권6호
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• pp.476-483
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• 2017

In this paper, a voltage-based model predictive control (MPC) scheme for a modular multilevel converter is used to reduce switching loss. The proposed method calculates an offset voltage that clamps the switching operation of submodules in which the current greatly flows at every sampling period by using the reference phase voltage and the reference phase current. To use the offset voltage, the proposed method converts the current-based MPC to the voltage-based MPC. The proposed voltage-based MPC then generates a new reference pole voltage that clamps the switching of submodules by applying the calculated offset voltage to the phase voltage. Therefore, the proposed method can reduce the switching loss by stopping the switching operation of submodules in which the current greatly flows. The switching loss reduction effect of the proposed method is verified by comparing its loss data with those of the conventional MPC method.

• 전력전자학회논문지
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• 제4권1호
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• pp.19-25
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• 1999

본 연구는 새로운 영전압, 영전류 스위칭 Forward 컨버터에 관한 것으로 종래의 하드 스위칭(Hard-Switching) Forward 컨버터에 있어서 Turn-off 및 Turn-off시 발생되는 스위칭 손실 및 출력 다이오드 역회복 특성에 따른 손실증가와 스위칭시 발생되는 기생진동을 Forward 컨버터에 있어서 1차측 주 스위칭소자 및 2차측 출력 정류다이오드와 병렬로 무손실 스너버를 적용함으로써 Forward 컨버터의 1차측 스위칭 소자의 Turn-off 및 Turn-on시 영전압, 영전류 스위칭을 이룰 수 있고, 출력 정류다이오드도 영전압, 영전류 스위칭 됨으로 다이오드의 역회복손실 및 기생 진동에 따른 EMI(Electro-Magnetic Interference)를 줄일 수 있는 무손실 스너버 적용 영전압, 영전류 스위칭 Forward 컨버터에 관한 것이다.

• 전력전자학회논문지
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• 제21권2호
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• pp.117-125
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• 2016

In this paper, the inverter switch losses of BLDC motor for three types of PWM methods and power devices were analyzed. When the BLDC motor is driven at low currents, the inverter switch losses for MOSFET are low because MOSFET operates like resistance. However, the inverter switch losses for IGBT are higher than MOSFET due to its large turn-off losses. Moreover, synchronous rectification switching method is adaptable because MOSFET has 2-channel. So, MOSFET can be driven with more low impedance and losses. For low power inverter with MOSFET, the power losses of unified PWM are lower than that of unipolar and bipolar PWM. Proposed method and losses analysis results are verified by examination and simulation using Matlab/Simulink.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 전력전자학술대회 논문집
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• pp.520-524
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• 2001

Recently, the demand of large capacity SMPS for industrial area is increasing. Full-bridge dc-dc converter with IGBT is most widely used for large capacity SMPS because IGBT has a low-conduction loss and large current capacity, But most large capacity Full-bridge do-dc converter using IGBT has low operating frequency because of switching loss at IGBT especially at turn-off by current tail and it's cause of relatively big converter size. MOSFET has low switching losses has been widely used for high frequency SMPS but it has a problem to apply to large capacity SMPS because it has large conduction resistance causing large on-time losses. In this paper, for reduction losses at switching device, MOSFET is applied at parallel with IGBT in full-bridge dc/dc converter.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권5호
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• pp.269-277
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• 1999

In this paper, a novel dead time minimization algorithm is proposed for improving the output waveform of an inverter. The adverse effects of the dead time are mainly described by the voltage drop and the distortion factor of waveforms. The principle of the proposed algorithm is organized with forbidding unnecessary firings fo the inverter switches which are not conducted even though the gate signal is impressed. The proposed methods are explained with the conduction mode of output currents. The H/W and S/W implementation method of the proposed algorithm are also presented. The validity of the proposed algorithm is verified by comparing the simulation and experimental results with conventional methods. It can be concluded from the results that the proposed algorithm has the advantage which is able to reduce the harmonics in the output voltages and which the output voltage can nearly be equal to the reference value. Another advantage of the proposed method is the reduction of total numbers of switching so that the switching losses of inverter drives can be minimized.

• 전력전자학회논문지
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• 제24권4호
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• pp.259-267
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• 2019

An active clamp flyback (ACF) converter applies a clamp circuit and circulates the energy of leakage inductance to the input side, thereby achieving a zero-voltage switching (ZVS) operation and greatly reducing switching losses. The switching losses are further reduced by applying a gallium nitride field effect transistor (GaN-FET) with excellent switching characteristics, and ZVS operation can be accomplished under light load with boundary conduction mode (BCM) operation. Optimal design is performed on the basis of loss analysis by selecting magnetization inductance based on BCM operation and a clamp capacitor for loss reduction. Therefore, the size of the reactive element can be reduced through high-frequency operation, and a high-efficiency and high-power-density converter can be achieved. This study proposes an optimal design for a high-efficiency and high-power-density BCM ACF converter based on GaN-FETs and verifies it through experimental results of a 65 W-rated prototype.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2008년도 하계학술대회 논문집
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• pp.28-30
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• 2008

This paper proposes soft switching boost converter operating in zero current switching(ZCS) mode for photovoltaic and fuel cell power generation. The proposed topology is capable of reducing the size, and capability of passive element by using soft switching, and it allows for reduction of IGBT switching losses, for the increased of switching frequency. A detail mode analysis of operating in presented. We present the converter topology, principle of operation and simulation results obtained from the PSIM simulator. The performance of the proposed technique in evaluation on 1kW(380V,2.6A) experimental prototype circuit operating at 30kHz.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 A
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• pp.379-381
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• 1994

This paper is concerned with a zero-voltage soft-switching PWM DC-DC high-pelter converter using IGBTs, which Bakes the most of the parastic LC parameters of high-voltage transformer link, for diagnostic X-Ray power generator. The converter circuit basically utilizes phase-shift pulse width modulated series resonant full-bridge PWM DC-DC high-Power converter operating at a constant frequency:20kHz. This technique brings about dramatic decreases in the switching losses of power devices and their electrical stresses as compared with the commonly-used hard-switching PWM DC-DC power converter. The high-frequency switching operation of the converters has some effective advantages, which consist in the physical reduction in size and weight and lowered acoustic noise.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.264-269
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• 1998

A proposed soft-switching buck-boost PWM converter has a lot of advantages, Viz., electric isolation, a high power factor, low switching losses, low EMI noise, reduction of the voltage and current stresses, etc. In a new PFC converter, the switching device is replaced by the loss-less snubber circuit to achieve the zero voltage switching (ZVS) at the maximum current. However, the charging current of the capacitor in the loss-less snubber circuit distorts the input current waveforms. To improve the input current waveform, a new duty factor control method is proposed in this paper.