• Progress in Superconductivity and Cryogenics
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• v.2 no.2
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• pp.11-14
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• 2000

We fabricated a resistive superconducting fault current limiter (SFCL) of meander type based on a YBCO film. In order to disperse the heat generated at hot spots in the YBCO film the film was coated with a gold shunt layer. When diodes were inserted in the parallel circuit to restrict the temperature increase in the SFCL element by reducing power supply cycles, the voltage could be increased to $\sqrt{2}$ times with the same quench resistance at a half and full cycles.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.91-94
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• 2000

We fabricated resistive super- conducting fault current limiters (SFCL) based on YBCO thin films grown on 2" diameter $Al_{2}O_{3}$ substrates. Two SFCLs with nearly identical properties. two SFCLs with nearly identical properties were connected in series to investigate simultaneous quenching. There was a difference of several half cycles in their quench starting time, although the difference was not more than 0.1 msec when they were operated separately. This imbalance was removed by connecting a shunt resistor to an SFCL in parallel. Increased power input at high voltages also reduced the initial imbalance in power dissipation. Further efforts on the simultaneous quench in SFCLs connected in series are on the way through methods such as the artificial control of quench speed.peed.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.436-439
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• 1999

This paper present a study on the interference levels on the communication lines, which are parallel to the electrified rails. The interference study is carried out using a circuit model approach. First, the self and shunt impedances of all the conductors in the rail system and the mutual impedances between different conductors are computed. Several different scenarios are analyzed, including the load condition and a few fault conditions with different fault locations. The induced potentials on the communication cables are computed. The effect of the buried ground wires is also analyzed by comparing the results with and without the presence of the ground wires. The results presented in the paper can be used as a reference for estimating interference levels in similar rail systems.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.925-927
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• 2000

We fabricated a resistive superconducting fault current limiter of meander type based on a YBCO film. In order to disperse the heat generated at hot spots in the YBCO film the film was coated with a gold shunt layer. When diodes were inserted in the parallel circuit to restrict the temperature increase in the SFCL element by reducing power supply cycles, the voltage could be increased to $\sqrt{2}$ times with the same quench resistance at a half and full cycles.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.26 no.10
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• pp.102-110
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• 2012

This paper propose the advanced topology of UPQC, its DC link is connected with Lithium battery, to compensate the momentary interruptions. The proposed system can be operated as UPS mode using the parallel inverter, which control the charge or discharge of battery, in case of the interruption. We dvelop 100kVA UPQC using the proposed topology to rise the power quality and the reliability of Microgrid. We verify its usefulness through voltage compensation test, UPS operation test and etc. using Microgrid test facility.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1553-1562
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• 2017

For the purpose of enhancing the performance of the shunt active power filter (APF), this paper presents a novel Fast Weighted Compound Control (FWCC) strategy based on the synchronous frame. In this control strategy, the proposed new repetitive controller can work faster and more stably by reducing the internal model cycle and introducing a damping coefficient. In addition, the harmonic detector can be removed to simplify the structure of the APF owing to the improvements. Furthermore, a proportional-integral (PI) controller is added to work in parallel with the repetitive controller by using a weighted ratio. Then, a convergence speed analysis and design algorithm are given in detail. Simulation and experimental results show that the harmonic distortion is reduced from 2.91% to 1.89%. In addition, the content for each of the characteristic harmonic orders has decreased by more than three times.

• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.244-260
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• 2018

Issues in the electrical characterization of semiconducting photoanodes in a photoelectrochemical (PEC) cell, such as the cell geometry dependence, scan rate dependence in DC measurements, and the frequency dependence in AC measurements, are addressed, using the example of a $TiO_2$ photoanode. Contrary to conventional constant phase element (CPE) modeling, the capacitive behavior associated with Mott-Schottky (MS) response was successfully modeled by a Havriliak-Negami (HN) capacitance function-which allowed the determination of frequency-independent Schottky capacitance parameters to be explained by a trapping mechanism. Additional polarization can be successfully described by the parallel connection of a Bisquert transmission line (TL) model for the diffusion-recombination process in the nanostructured $TiO_2$ electrode. Instead of shunt CPEs generally employed for the non-ideal TL feature, TL models with ideal shunt capacitors can describe the experimental data in the presence of an infinite-length Warburg element as internal interfacial impedance - a characteristic suggested to be a generic feature of many electrochemical cells. Fully parametrized impedance spectra finally allow in-depth physicochemical interpretations.

• Progress in Superconductivity
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• v.3 no.2
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• pp.241-246
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• 2002

We have performed the current and voltage loading tests of resistive superconducting fault current limiters (SFCLS) based on $YBa_2$$Cu_3$$O_{7}$(YBCO) films with the diameter of 2 inch. The SFCL consists of meander-type YBCO stripes covered with 200 nm Au layer grown in situ for current shunt and heat dispersion at hot spots. The minimum quench current of an SFCL unit was about 25 Apeak. Seven SFCL units were connected in parallel fur the current load ing tests at power source of 100 $V_{rms}$ $/2,000A_{rms}$. This SFCL units had maximum limiting current of 170 Apeak during the fault instant and then successfully controlled the fault current below 100 Apeak within 1~2 msec after short circuit. Increased short current also reduced the quench completion time with little change of current limiting characterization. We connected six SFCL units in series fur the voltage loading tests at power source of $1,200 V_{rms}$/170 $A_{rms}$ at this time. The shunt resistors were inserted into each SFCL unit to eliminate power imbalance originated from serial connection of SFCL units. Each SFCL unit was quenched simultaneously during the fault condition. The current increased up to 40 $A_{peak}$ and decreased to 14 $A_{peak}$ after 3 cycles. Quench was completed within 1 msec after the fault. We confirmed operating characteristics of 140 kVA($120 A_{rms}$ $\times$ 1,200 $V_{rms}$) SFCL and presented the manufacturing possibility of 3.3 kV SFCL using 4 inch YBCO films.BCO films.lms.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.5.1-5.1
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• 2009

Organic photovoltaic (OPV)cells have attracted considerable attention due to their potential for flexible, lightweight, and low-cost application of solar energy conversion. Since a 1% power conversion efficiency (PCE) OPV based on a single donor-acceptor heterojunction was reported by Tang, the PCE has steadily improved around 5%. It is well known that a high parallel (shunt)resistance and a low series resistance are required simultaneously to achieve ideal photovoltaic devices. The device should be free of leakage current through the device to maximize the parallel resistance. The series resistance is attributed to the ohmic loss in the whole device, which includes the bulk resistance and the contact resistance. The bulk resistance originated from the bulk resistance of the organic layer and the electrodes; the contact resistance comes from the interface between the electrodes and the active layer. Furthermore, it has been reported that the bulk resistance of the indium tin oxide (ITO) of the devices dominates the series resistance of OPVs for a large area more than $0.01\;cm^2$. Therefore, in practical application, the large area of ITO may significantly reduce the device performance. In this work, we investigated the effect of sheet resistance ($R_{sh}$) of deposited ITO on the performance of OPVs. It was found that the device performance of polythiophene-fullerene (P3HT:PCBM) bulk heterojunction OPVs was critically dependent on Rsh of the ITO electrode. With decreasing $R_{sh}$ of the ITO from 39 to $8.5\;{\Omega}/{\square}$, the fill factor (FF) of OPVs was dramatically improved from 0.407 to 0.580, resulting in improvement of PCE from $1.63{\pm}0.2$ to $2.5{\pm}0.1%$ underan AM1.5 simulated solar intensity of $100\;mW/cm^2$.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.2
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• pp.133-138
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• 2014

This paper proposes a low power-loss averaging current mode control using a resistor and bypass switch. Generally, current sensing method using a resistor has a disadvantage of power loss which degrades the efficiency of the entire systems. On the other hand, proposed measurement technique operating with bypass-switch connected in parallel with sensing resistor can reduce power loss significantly the current sensor. An analog-circuited bypass driver is implemented and used along with an average-circuit mode controller. The bypass switch bypasses the sensing current with a small amount of power loss. In this paper, a 50[W] prototype average current mode boost converter has been implemented for the experimental verification.