• Proceedings of the KIEE Conference
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• 1999.07f
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• pp.2691-2694
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• 1999

The multi-resonant converter(MRC) can reduce the switching losses exiting in a converter, so it is capable of operating at a high frequency. Such a few MHz high frequency application provides a high power density [$W/inch^{3}$]. But the high voltage stress across a switch of the resonant circuit is about 4$\sim$5 times the input voltage, it causes increasing of the conduction loss in MRC. In this paper, the mode analysis for the suggested AT Forward MRC with low voltage stress is discussed. The operational modes of the AT Forward MRC are divided to 8 equivalent modes according to the two switching sequences, Each mode is analyzed over all of the paper.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2000.11a
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• pp.188-192
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• 2000

This paper presents a novel prototype of soft-switching PWM Full-bridge converter which incorporates active power switches in series with each rectifier diode in transformer secondary side. Switching and conduction losses of all the switches and devices are reduced as well as commutating current and circulating current flowing through transformer as compared with conventional converter. And duty ratio of primary switches is constant for maximum voltage conversion ratio. But this converter can be varied output by duty ratio of secondary switches. Operation principles basically the same as that of the PWM Full-bridge converter published previously. The operating characteristics of this converter are illustrate and discussed including the simulated analysis.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.589-592
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• 2002

The CCM (Continuous Conduction Mode) boost topology is generally used in the PFC (Power Factor Correction) regulator of household air-conditioning systems. There are three kinds of power devices-bridge rectifier diodes, FRDs (Fast Recovery Diodes), and IGBTs (or MOSFETs) - used In a boost PFC regulator. Selecting the appropriate device is very cumbersome work, specially, in the case of FRDs and IGBTs, because there are several considerations as described below: 1) High frequency leakage current regulation (conducted and radiated EMI regulation) 2) Power losses and thermal design 3) Device cost. It should be noted that there are trade-offs between the power loss characteristic of 2) and the other characteristics of 1) and 3). This paper presents a detailed evaluation by using several types of power devices, which can be unintentionally used, to show that optimal selection can be achieved. Based on the given thermal resistances, thermal analysis and design procedures are also described from a practical viewpoint.

• Proceedings of the KIPE Conference
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• 2003.07b
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• pp.777-780
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• 2003

In this paper, an improved full wave mode ZVT-PWM DC-DC Converter is presented to maximize the regeneration ratio of resonant energy by only putting an additional diode in series with auxiliary switch. The operation of auxiliary switch in a half wave mode makes possible the soft switching condition of all switches. Furthermore, the increase of the regeneration ratio to resonant energy results in low conduction losses and minimum voltage and current stresses. The operation principles of the proposed converters are analyzed using the PWM boost converter topology as an example. Theoretically analysis and experimental results verify the validity of the boost converter topology with the proposed full wave mode ZVT-PWM converters

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.518-523
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• 1998

In this paper, a noble dead time minimization algorithm is presented for developing the outputs of inverters. The adverse effects of the dead time are examined. The principle of the proposed algorithm is explained with the conduction modes of the output currents. The H/W and the S/W construction method of the proposed algorithm are also presented. The validity of the proposed algorithm is verified by comparing simulation and experimental results with those of the conventional methods. It can be concluded from the results that the proposed algorithm have the virtue which is able to ruduce the numbers of inverter switching and the harmonics in the output voltages, and which make the output voltage equal to the reference value.

• Journal of Electrical Engineering and Technology
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• v.5 no.3
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• pp.477-483
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• 2010

This paper is studied on a novel buck-boost isolated converter for high efficiency and high power factor. The switching devices in the proposed converter are operated by soft switching technique using a new quasi-resonant circuit, and are driven with discontinuous conduction mode (DCM) according to pulse width modulation (PWM). The quasi-resonant circuit makes use of a step up-down inductor and a loss-less snubber capacitor. The proposed converter with DCM also simplifies the requirement of control circuit and reduces a number of control components. The input ac current waveform in the proposed converter becomes a quasi sinusoidal waveform in proportion to the magnitude of input ac voltage under constant switching frequency. As a result, it is obtained by the proposed converter that the switching power losses are low, the efficiency of the converter is high, and the input power factor is nearly unity. The validity of analytical results is confirmed by some simulation results on computer and experimental results.

• Proceedings of the KIEE Conference
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• 2002.04a
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• pp.213-215
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• 2002

This paper presents grid connected photovoltaic inverter system using a new Zero-Current-Transition(ZCT) technique. The main switches of the proposed grid connected inverter are turned off under the zero current condition by operating the auxiliary circuit and also all semiconductor devices, switches and diodes, are applied to low rated voltage regardless of the load condition. In additionally, the proposed ZCT scheme has advantages, which are without the additional current stresses and the conduction losses on the main switches during the resonance period of the auxiliary circuit. The simulation was performed to verify the validity of the proposed grid connected photovoltaic ZCT inverter system.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.8
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• pp.423-429
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• 2006

Recently, the high frequency isolated boost DC/DC converter has been widely used for the PCS (Power Conditioning System) system because of its small size and low cost. However, the high frequency isolated boost DC/DC converters applied the conventional voltage-fed converter and current-fed converter have the problems such as the high conduction losses and the surge voltage due to the high circulating current and the leakage inductance, respectively. To overcome this problems, in this paper the secondary LLC resonant converter is proposed, and the experimental results of the secondary LLC series resonant converter for boost DC/DC converter are verified on the simulation based on the theoretical analysis and the 700W experimental prototype.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1065-1066
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• 2006

The multi-resonant converter minimizes the parasitic oscillations using the resonant tank circuit absorbed parasitic reactances in a converter. So the converter can be operated at a high frequency and it provides a high efficiency because the switching power losses are reduced effectively. However, the high resonant voltage stress of semiconductors leads to the conduction loss. In this paper, it is proposed the novel flyback multi-resonant converter. The converter input is divided by two series input capacitors. And also the resonant stress is reduced to 2-3 times input voltage without any complexity and it provides the various circuit schemes in lots of applications. The proposed converters are verified through simulation and experiment.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1010-1011
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• 2006

A new soft switched active snubber circuit is proposed to achieve zero voltage and zero current switching for all the switching devices in PWM DC-DC converters. The unique location of the snubber capacitor and inductor ensures low current/voltage stresses and commutation losses. With a saturable reactor, the conduction loss of the auxiliary switch could be further minimized. A boost converter adopting this technique is presented as an example, to illuminate its operation principles and derive the design procedures. Simulation and hardware implementation have been made to validate its performance. Some other basic PWM DC-DC topologies using the proposed snubber have also been given.