• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.4
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• pp.668-675
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• 2001

Recently, the performance of the commercial PCS(Personal Communication Service) system has been improved to the uppermost limit and ultimately the next generation mobile communication is to be realized by IMT-2000 (International Mobile Communication-2000) to provide multimedia services. Therefore, the new type receiving system is researched actively and one of the most important part in a receiver is direct conversion method. The direct conversion method is suitable for low power consumption, small size, MMIC, and low price, which is to be adopted to the next generation mobile communication systems. In this case, however, several problems occur due to DC-offset. The DC-offset suppresses amplification of the required signal because of the leakage signal of frequency synthesizer in the system. In this thesis, the removing method of DC-offset was considered. There are four removing techniques of DC-offset, which are AC-coupling, large capacitor, DC-feedback loop, and DC-free coding. Among these, the AC-coupling method is the most simplest method and the DC-feedback loop method has the best performance. Then, the performance of the AC-coupling method and DC-feedback loop method are evaluated by HP's ADS simulation tool. As a result, the AC-coupling method cannot be used to the digital communication systems due to data loss. On the other hand, it was confirmed that the DC-feedback loop method is suitable for the direct conversion receiver.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.61 no.4
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• pp.192-198
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• 2012

Switch losses directly affect the efficiency of power conversion systems and those have big differences according to the power consumed by load systems and the structures of power conversion circuits. In this paper, analyses for switch losses in DC link converter are performed based on the circuit structures of the DC/DC converter in photovoltaic generation system whose output power is varied according to the amount of solar radiation, temperature and partial shade on the solar modules. Boost converter is adopted as a DC link converter topology of the photovoltaic generation system and the loss analyses for the switches used in the boost converters are performed according to the circuit structures. Analyses like the things performed in this paper will be a prerequisite to designing the photovoltaic generation system whose output power is changed according to the environmental variations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.16-21
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• 2012

The growth in IT industry has brought a corresponding rise in the number of connected digital devices in the distribution network. These digital loads lead to AC to DC conversion losses in order to supply power to them. The more the renewable energies and plug-in electrical vehicles penetrated our lives, the more the electrical losses are caused by AC to DC conversion process. Hence, this paper suggests the methodology for evaluating the amount of power supplied according to the ratio of DC power supply and performs an economic analysis of DC distribution system considering grid parity. In here, the cost of carbon emission reduced by renewable energy is also concerned.

• Journal of Power Electronics
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• v.3 no.4
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• pp.249-258
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• 2003

This paper presents a high-efficient and cost effective three-phase AC/DC-DC/AC power conversion system with a single two-switch type active Auxiliary Resonant DC Link (ARDCL) snubber circuit, which can minimize the total power dissipation. The active ARDCL snubber circuit is proposed in this paper and its unique features are described. Its operation principle in steady-state is discussed for the three phase AC/DC-DC/AC converter, which is composed of PWM rectifier as power factor correction (PFC) converter, sinewave PWM inverter. In the presented power converter system not only three-phase AC/DC PWM rectifier but also three-phase DC/AC inverter can achieve the stable ZVS commutation for all the power semiconductor devices. It is proved that the proposed three-phase AC/DC-DC/AC converter system is more effective and acceptable than the previous from the cost viewpoint and high efficient consideration. In addition, the proposed two-switch type active auxiliary ARDCL snubber circuit can reduce the peak value of the resonant inductor injection current in order to maximize total system actual efficiency by using the improved DSP based control scheme. Moreover the proposed active auxiliary two-switch ARDCL snubber circuit has the merit so that there is no need to use any sensing devices to detect the voltage and current in the ARDCL sunbber circuit for realizing soft-switching operation. This three-phase AC/DC-DC/AC converter system developed for UPS can achieve the 1.8% higher efficiency and 20dB lower conduction noise than those of the conventional three-phase hard-switching PWM AC/DC-DC/AC converter system. It is proved that actual efficiency of the proposed three-phase AC/DC-DC/AC converter system operating under a condition of soft switching is 88.7% under 10kw output power.

• Journal of Power Electronics
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• v.5 no.3
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• pp.233-239
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• 2005

In this paper, a new conceptual circuit configuration of a 3-phase voltage source, soft switching AC-DC-AC converter using an IGBT module, which has one ARCPL circuit and one ARDCL circuit, is presented. In actuality, the ARCPL circuit is applied in the 3-phase voltage source rectifier side, and the ARDCL circuit is in the inverter side. And more, each power semiconductor device has a novel clamp snubber circuit, which can save the power semiconductor device from voltage and current across each power device. The proposed soft switching circuits have only two active power semiconductor devices. These ARCPL and ARDCL circuits consist of fewer parts than the conventional soft switching circuit. Furthermore, the proposed 3-phase voltage source soft switching AC-DC-AC power conversion system needs no additional sensor for complete soft switching as compared with the conventional 3-phase voltage source AC-DC-AC power conversion system. In addition to this, these soft switching circuits operate only once in one sampling term. Therefore, the power conversion efficiency of the proposed AC-DC-AC converter system will get higher than a conventional soft switching converter system because of the reduced ARCPL and ARDCL circuit losses. The operation timing and terms for ARDCL and ARCPL circuits are calculated and controlled by the smoothing DC capacitor voltage and the output AC current. Using this control, the loss of the soft switching circuits are reduced owing to reduced resonant inductor current in ARCPL and ARDCL circuits as compared with the conventional controlled soft switching power conversion system. The operating performances of proposed soft switching AC-DC-AC converter treated here are evaluated on the basis of experimental results in a 50kVA setup in this paper. As a result of experiment on the 50kVA system, it was confirmed that the proposed circuit could reduce conduction noise below 10 MHz and improve the conversion efficiency from 88. 5% to 90.5%, when compared with the hard switching circuit.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.6
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• pp.43-48
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• 2006

In this paper, the rectenna converting 2.45[GHz] microwave into DC power is designed and fabricated for wireless power transmission using microwave and the methode for impedance matching and tuning are proposed in order to maximize RF-DC conversion efficiency. The fabricated rectenna can be easily tuned by using a broad open stub and has the RF-DC conversion efficiency up to 59[%] when the 5[dBm] input power is applied. The 2.2[V], 1.5[mW] DC level, in the 1[m] distance between the transmitter and the receiver can be obtained and this value is avaliable in the small power digital system.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1146-1147
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• 2008

PV Power Conditioning System (PCS) must have high conversion and low cost. Generally, PV PCS uses either a single converter or multilevel module integrated converter (MIC). Each of these approaches has both advantage and disadvantage. For a high conversion efficiency and low cost of PV module, this paper proposes series connection of module integrated DC-DC converter's output with PV panel. Output voltage of PV panel is connected to the output capacitor of flyback converter. Thus, converter's output voltage is added to the output voltage of PV panel. Isolated DC-DC converter generates only the difference voltage between the PV panel voltage and the required total output voltage. This method reduces power level of DC-DC converter and enhances the energy conversion efficiency compared with conventional DC-DC converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.336-344
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• 2017

This paper presents the three-port DC-DC converter modeling and controller design procedure, which is part of the solid-state transformer (SST) to interface medium voltage AC grid to bipolar DC distribution network. Due to the high primary side DC link voltage, the proposed converter employs the three-level neutral point clamped (NPC) topology at the primary side and 2-two level half bridge circuits for each DC distribution network. For the proposed converter particular structure, this paper conducts modeling the three winding transformer and the power transfer between each port. A decoupling method is adopted to simplify the power transfer model. The voltage controller design procedure is presented. In addition, the output current sharing controller is employed for current balancing between the parallel-connected secondary output ports. The proposed circuit and controller performance are verified by experimental results using a 30 kW prototype SST system.

• Journal of information and communication convergence engineering
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• v.5 no.4
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• pp.358-361
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• 2007

We report on a new type dc-dc converter design that combines the advantage of dc ripple noise elimination and high efficiency. As potential low cost solar cells, DSC module and the panel's system efficiency and stability are still critical problems to the way of marketing. In this study, a new three-step dc-dc converter scheme with the phase-shift-carrier technology is proposed to apply for solar power system. We have achieved power conversion efficiency around 94.88%.

• Journal of IKEEE
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• v.25 no.1
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• pp.218-228
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• 2021

This paper presents the high-efficiency DC-DC converter using the multi-resonant-circuit. The proposed converter has the power topology of half-bridge and utilizes the multi-resonant-circuit that is composed of 2 inductors (LL) and 1 capacitor (C) to achieve high-efficiency. The multi-resonant-circuit forms each resonant circuit of series circuit type with each resonant frequency, according to the operation modes. This paper first describes the operation pirinciples of proposed converter by the operation modes and steady-state fundamental approximation modelling. Then it shows a design example of the proposed converter based on the principles. And it is validated that the proposed converter has the operation characteristics of high-efficiency DC-DC power conversion through the experimental results of prototype converter implemented by the designed circuit parameters.