• Journal of Power Electronics
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• v.10 no.1
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• pp.27-33
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• 2010

This paper presents a bidirectional DC-DC converter suitable for low-voltage super capacitor-based electric energy storage systems. The DC-DC converter presented here consists of a full-bridge circuit and a current-fed push-pull circuit with a high frequency (HF) transformer-link. In order to reduce the device-conduction losses due to the large current of the super capacitor as well as unnecessary ringing, synchronous rectification is employed in the super capacitor-charging mode. A wide range of voltage regulation between the battery and the super capacitor can be realized by employing a Phase-Shifting (PS) Pulse Width Modulation (PWM) scheme in the full-bridge circuit for the super capacitor charging mode as well as the overlapping PWM scheme of the gate signals to the active power devices in the push-pull circuit for the super capacitor discharging mode. Essential performance of the bidirectional DC-DC converter is demonstrated with simulation and experiment results, and the practical effectiveness of the DC-DC converter is discussed.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.505-507
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• 2008

A conventional active-clamp forward (ACF) converter is a favorable candidate in low-to-medium power applications. However, the switches suffer from high voltage stress, i.e., sum of the input voltage and the reset capacitor voltage. Therefore, it is not suitable for high input voltage applications such as a front-end converter of which the input voltage is about 400-$V_{dc}$. To solve this problem, three-switch ACF (TS-ACF) converter, which employs two main switches and one auxiliary switch with low voltage stress, is proposed. Utilizing low-voltage rated switches, the proposed converter is promising for high input voltage applications with high efficiency and low cost.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1277-1287
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• 2016

This study proposes a novel isolated high step-up galvanic converter, which is suitable for renewable energy applications and integrates a boost converter, a coupled inductor, a charge pump capacitor cell, and an LC snubber. The proposed converter comprises an input inductor and thus features a continuous input current, which extends the life of the renewable energy chip. Furthermore, the proposed converter can achieve a high voltage gain without an extremely large duty cycle and turn ratio of the coupled inductor by using the charge pump capacitor cell. The leakage inductance energy can be recycled to the output capacitor of the boost converter via the LC snubber and then transferred to the output load. As a result, the voltage spike can be suppressed to a low voltage level. Finally, the basic operating principles and experimental results are provided to verify the effectiveness of the proposed converter.

• Journal of Electrical Engineering and Technology
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• v.8 no.3
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• pp.428-435
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• 2013

Flexible AC Transmission System (FACTS) application study on enhancing the flexibility of AC power system has continued to make progress. A thyristor-controlled series capacitor (TCSC) is a useful FACTS device that can control the power flow by adjusting line impedances and minimize the loss of power flow and voltage drop in a transmission system by adjusting line impedances. Reduced power flow loss leads to increased loadability, low system loss, and improved stability of the power system. This study proposes the optimal location and compensation rate method for TCSCs, by considering both the power system loss and voltage drop of transmission systems. The proposed method applies a multi-objective function consisting of a minimizing function for power flow loss and voltage drop. The effectiveness of the proposed method is demonstrated using IEEE 14- and a 30-bus system.

• Journal of Power Electronics
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• v.14 no.5
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• pp.834-841
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• 2014

This paper proposes new active switched-capacitor and switched-inductor Z-source inverter (ASC/SL-ZSI) topologies, which can provide a higher boost ability with a small shoot-through time. The proposed ASC/SL-ZSIs inherit all of the advantages of the classical ZSI, and have a stronger voltage boost inversion ability when compared with the classical ZSI. Thus, the output ac voltage quality is significantly improved. In addition, more cells can be cascaded in the impedance network in order to obtain a very high boost ability. The proposed topologies can be applied to photovoltaic or fuel-cell generation systems with low-voltage renewal sources due to their wide range of obtainable voltages. Both simulations and the experimental results are carried out in order to verify performance of the proposed topologies.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1656-1663
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• 2016

A capacitive wireless power transfer (C-WPT) system uses an electric field to transmit power through a physical isolation barrier which forms a pair of ac link capacitors between the metal plates. However, the physical dimension and low dielectric constant of the interface medium severely limit the effective link capacitance to a level comparable to the main switch output capacitance of the transmitting circuit, which thus narrows the soft-switching range in the light load condition. Moreover, by fundamental limit analysis, it can be proved that such a low link capacitance increases operating frequency and capacitor voltage stress in the full load condition. In order to handle these problems, this paper investigates optimal design of double matching transformer networks for C-WPT. Using mathematical analysis with fundamental harmonic approximation, a design guideline is presented to avoid unnecessarily high frequency operation, to suppress the voltage stress on the link capacitors, and to achieve wide ZVS range even with low link capacitance. Simulation and hardware implementation are performed on a 5-W prototype system equipped with a 256-pF link capacitance and a 200-pF switch output capacitance. Results show that the proposed scheme ensures zero-voltage-switching from full load to 10% load, and the switching frequency and the link capacitor voltage stress are kept below 250 kHz and 452 V, respectively, in the full load condition.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.11
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• pp.676-680
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• 2016

This paper describes a low voltage detection circuit used in the semiconductor chips. The circuit was composed of a detection part of the CMOS structure as three stages and two inverters. The output of the low voltage detection circuit become to 'high' from 'low', when the power supply voltage falls below 80%. When the power supply voltage is 5 V, it was detected at 4 V point. The proposed low voltage detection circuit can be easily applied only by changing the resister and the capacitor without structural change in a wide range of power supply voltage.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.819-822
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• 1998

A new active power filter (APF) circuit with a current compesation estimation method is proposed. The current compensation estimation method replaces a current sensor with an estimating circuit and therefore reduces the implementation cost In addition, a simple control scheme, based on the energy balance concept, is adopted to control the voltage of a DC capacitor. Therefore energy change in the DC capacitor can be compensanted in the next cycle. Since a sampling technique is used, a larger DC capacitor voltage ripple can be permissible and a relatively smaller DC capacitor can be used. The proposed method has advantages of the reduction of one current sensor, low implementation cost, and fast transient responses. The theoretical analysis and simulation results are given. The proposed control method is successfully verified by computer simulation.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.102-105
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• 2003

The leakage inductance of the High frequency Transformer(HFT) in the flyback topology can be used an inductor of the Low Pass Filter(LPF) to reduce ripple and ripple noise in the output voltage. But, the values of leakage inductance and magnetizing inductance in the HFT are within $\pm20[{\%}]$). And the operating temperature of the HFT increased by the leakage inductance. Therefore, the leakage inductance of the HFT in the flyback topology has minimum and the LPF has non-polarity ceramic capacitor in the output stage. In this paper, the LPF in the flyback topoBogy takes PCB capacitor using double layer of PCB without non-polarity ceramic capacitor. Its experimental results show the reduced ripple noise and the reduced ripple in the output stage.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.399-402
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• 2002

In this paper, the novel method is proposed to measure the capacitance of the dc link capacitor Advantage of the method is not to separate capacitor from 3-phase AC/DC/AC converters. In the proposed method, a specific low frequency current is injected to oscillate the voltage of dc capacitor at no load condition. The capacitance of dc capacitor is calculated with the effective values of this ripple voltage and current. The validity of the proposed method is confirmed by PSIM simulation.