• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05b
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• pp.19-22
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• 2004

The resonant planar transformer, which had power capacity of 300 W, input voltage of 220 V, output voltage of 15 V, and switching frequency of 500 kHz, was designed and manufactured by using the planar core with large effective area and the flat copper lead frames for miniaturization and high efficiency of the switching mode power supply (SMPS). As well as, a resonant converter equipped with the above mentioned planar transformer was manufactured and electromagnetic characteristics were investigated. The numerical value of turns for 1st and 2nd winding were 12 and 2 respectively. The self inductance of 1st winding was 33.2 ${\mu}H$, very low leakage inductance of 1.27 ${\mu}H$, and the coupling factor of 0.98 were obtained at switching frequency of 300 kHz. The high efficiency of 88.21 % for the SMPS equipped with planar transformer was obtained at power capacity of 300 W.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.1 no.2
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• pp.27-32
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• 2008

A current research basically diverted towards an increase in the operational output with the minimization of the materials used, which ultimately scaled down the dimensions of ceramic electronic components. In this direction the nano-technology pave the revolutionary changes in particular the electronic industries. The applications of nano-sized particles or nano-sized materials are hence, playing a significant role for various purposes. The PZT(lead, zirconium, titanium) based ceramics which, are reported to be ferroelectric materials have their important applications in the areas of surface acoustic waves (SAW), filters, infrared detectors, actuators, ferroelectric random access memory, speakers, electronic switches etc. Moreover, these PZT materials possess the large electro mechanical coupling factor, large spontaneous polarization, low dielectric loss and low internal stress etc. Hence, keeping in view the unique properties of PZT piezoelectric ceramics we also tried to synthesize indigenously the small sized PZT ceramic powder in the laboratory by using the modified sol-gel approach. In this paper, propyl alcohol based sol-gel method was used for preparation of PZT piezoelectric ceramic. The powder obtained by this sol-gel process was calcined and sintering to reach a pyrochlore-free crystal phase. The characterization of synthesized material was carried out by the XRD analysis and the surface morphology was determined by high resolution scanning electron microscopy.

• Journal of Power Electronics
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• v.15 no.2
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• pp.366-377
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• 2015

In order to minimize switching losses for high power applications, a boost PFC rectifier with a novel passive lossless snubber circuit is proposed. The proposed lossless snubber is composed of coupled inductors merged into a boost inductor. This method compared with conventional methods does not need additional inductor cores and it reduces extra costs to implement a soft switching circuit. Especially, the proposed circuit can reduce the reverse recovery current of output diode rectifiers due to the coupling effect of the inductor. During turn-on and turn-off operating modes, the proposed PFC converter operates under soft switching conditions with high power conversion efficiency. In addition, the performance improvement and analysis of the operating effects of the coupled inductors were also presented and verified with a 3.3 kW prototype rectifier.

• Journal of Power Electronics
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• v.15 no.4
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• pp.1006-1017
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• 2015

This paper presents a finite control set model predictive control (FCS-MPC) strategy for the AC/DC matrix converter used in grid-connected battery energy storage system (BESS). First, to control the grid current properly, the DC current is also included in the cost function because of input and output direct coupling. The DC current reference is generated based on the dynamic relationship of the two currents, so the grid current gains improved transient state performance. Furthermore, the steady state error is reduced by adding a closed-loop. Second, a Luenberger observer is adopted to detect the AC input voltage instead of sensors, so the cost is reduced and the reliability can be enhanced. Third, a switching state pre-selection method that only needs to evaluate half of the active switching states is presented, with the advantages of shorter calculation time, no high dv/dt at the DC terminal, and less switching loss. The robustness under grid voltage distortion and parameter sensibility are discussed as well. Simulation and experimental results confirm the good performance of the proposed scheme for battery charging and discharging control.

• Journal of Power Electronics
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• v.18 no.1
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• pp.289-299
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• 2018

Electric-field coupled power transfer (ECPT) systems employ a high frequency electric field as an energy medium to transfer power wirelessly. Existing ECPT systems have made great progress in terms of increasing the transfer distance. However, the topologies of these systems are complex, and the transfer characteristics are very sensitive to variations in the circuit parameters. This paper proposes an ECPT system with a double-sided LC network, which employs a parallel LC network on the primary side and a series LC network on the secondary side. With the same transfer distance and output power, the proposed system is simpler and less sensitive than existing systems. The expression of the optimal driving voltage for the coupling structure and the characteristics of the LC networks are also analyzed, including the transfer efficiency, parameter sensitivity and total harmonic distortion. Then, a design method for the system parameters is provided according to these characteristics. Simulations and experiments have been carried out to verify the system properties and the design method.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1377-1379
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• 2005

독립형 태양광 발전시스템은 태양전지, 배터리, 충 방전 제어기, 컨버터, 부하로 나눌 수 있다. 태양광 발전은 비선형 전압전류 특성을 가지고 있기 때문에 발전효율을 최대한 높이기 위해 최대전력추종제어(MPPT)를 하게된다. 또한 부하가 여러 개일 경우에는 다양한 출력이 요구되는데, 이를 위해 강압 및 승압이 가능한 컨버터가 필요하게 된다. 그러나 다중부하에는 다수의 컨버터와 각각의 컨버터를 제어하기 위한 제어기가 필요하게 되므로 cost가 증가요인이 된다. 따라서 본 논문에서는 승 강압에 의한 다중출력을 갖는 병렬구조의 DC-DC컨버터를 제안하고자 한다. 제안된 컨버터는 입력전압을 승 강압하여 두 개의 출력전압을 갖는다. 강압동작은 일반적인 buck형 컨버터에 커패시터를 추가하여 구성하였고, 승압을 위해서는 리플율이 적은 Coupling inductor를 이용하고 커패시터를 추가하여 두 개의 컨버터를 병렬로 구성하였다. 컨버터의 병렬제어를 위해 제어기를 설계하고 이를 시뮬레이션 하였다.

• Journal of Radiation Protection and Research
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• v.8 no.2
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• pp.41-46
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• 1983

Annual collective dose within 50 miles radius of Ko-ri I reactor site due to normal airborne effluent discharges in 1979 has been estimated by AIRDOS-EPA computer code. Gaussian plume equation is used for estimation of both horizontal and vertical dispersion of radionuclide release into the atmosphere. Also, radionuclide concentrations in meat, milk, and fresh produce consumed by near-by population are estimated by coupling the output of the atmospheric transport models with the USNRC terrestrial food chain models. Annual collective doses are found to be $3.348{\times}10^{-1}$ whole body manrem and 84.95 thyroid manrem. Whole body manrem calculated by AIRDOS-EPA computer code do not differ greatly from that calculated by GASPAR computer code, but value for thyroid manrem have been estimated lower than that calculated by GASPAR computer code.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.158-158
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• 2019

Recent studies show the possibility of more frequent extreme events as a result of the changing climate. These weather extremes, such as excessive rainfall, result to debris flow, river overflow and urban flooding, which post a substantial threat to the community. Therefore, an effective flood model is a crucial tool in flood disaster mitigation. In recent years, a number of flood models has been established; however, the major challenge in developing effective and accurate inundation models is the inconvenience of running multiple models for separate conditions. Among the solutions in recent researches is the development of the combined 1D-2D flood modeling. The coupled 1D-2D river flood modeling allows channel flows to be represented in 1D and the overbank flow to be modeled over two-dimension. To test the efficiency of this approach, this research aims to assess the capability of HEC-RAS model's implementation of the combined 1D-2D hydraulic simulation of river overflow inundation, and compare with the results of GERIS and FLUMENS 2D flood model. Results show similar output to the flood models that had used different methods. This proves the applicability of the HEC-RAS 1D-2D coupling method as a powerful tool in simulating accurate inundation for flood events.

• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.63-67
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• 2013

We perform an optical vestigial sideband (VSB) filtering using a pair of Fabry-Perot (FP) filters. The transmittance curve of each FP filter is made to have sharp skirts using an offset between input and output coupling fibers. Moreover, the accurate periodicity of FP filters in the optical frequency domain enables the simultaneous VSB filtering of a large number of optical channels. With this VSB filtering technique, we transmit 12.5-GHz spaced $64{\times}12.4-Gb/s$ wavelength-division-multiplexing channels over a single-mode fiber up to 150 km without any dispersion compensations. When the channel spacing is reduced to 10 GHz, we achieve the spectral efficiency of 1 bit/s/Hz in conventional optical intensity modulation systems up to 125 km.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.4
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• pp.286-289
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• 2019

In this paper, we proposed a method to control input powers and receiver loads for maximum efficiency in multiple-input multiple-output(MIMO) wireless power transfer(WPT) systems. The input voltage ratio between transmitters and receiver loads for maximum transfer efficiency is derived in terms of figure of merits. The theoretically derived input voltages for the transmitters and optimum loads for the receivers were found to be similar to those obtained by a genetic algorithm. We demonstrate the effectiveness of the theory using a few design examples. Using the results obtained from this study, effective and simplified designs of MIMO WPT systems will be possible.