• Journal of Power Electronics
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• 제16권3호
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• pp.823-831
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• 2016

A high-efficiency method is proposed to suppress magnetic core imbalance in phase-shifted full-bridge (PSFB) converters. Compared with conventional solutions, such as controlling peak current mode (PCM) or adding DC blocking capacitance, the proposed method has several advantages, such as lower power loss and smaller size, because the additional current sensor or blocking capacitor is removed. A time domain model of the secondary side is built to analyze the relationship between transformer core imbalance and cathode voltage of secondary side rectifiers. An approximate control algorithm is designed to achieve asymmetric phase control, which reduces the effects of imbalance. A 60 V/15 A prototype is built to verify the proposed method. Experimental results show that the numerical difference of primary side peak currents between two adjacent cycles is suppressed from 2 A to approximately 0 A. Meanwhile, compared with the PCM solution, the efficiency of the PSFB converter is slightly improved from 93% to 93.2%.

• Journal of Power Electronics
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• 제13권3호
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• pp.329-338
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• 2013

In this paper, the charging characteristics of series resonant type high voltage capacitor chargers considering the transformer stray capacitance have been studied. The principles of operation for the four operational modes and the mode changes for the four different switching frequency sections are explained and analyzed in the range of switching frequency below the resonant frequency. It is confirmed that the average charging currents derived from the above analysis results have non-linear characteristics in each of the four modes. The resonant current, resonant voltage, charging current, and charging time of this capacitor charger as variations of the switching frequency, series parallel capacitance ratio ($k=C_p/C_s$), and output voltage are calculated. From the calculation results, the advantages and disadvantages arising from the parallel connection of this stray capacitance are described. Some methods to minimize charging time of this capacitor charger are suggested. In addition, the results of a comparative test using two transformers whose stray capacitances are different are described. A 1.8 kJ/s prototype capacitor charger is assembled with a TI28335 DSP controller and a 40 kJ, 7 kV capacitor. The analysis results are verified by the experiment.

• 전력전자학회논문지
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• 제25권1호
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• pp.37-43
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• 2020

This study proposes a 7kW low-voltage DC-DC converter (LDC) using a coupled inductor (CI) for heavy hydrogen electric transport vehicles. The LDC uses a phase-shift manner for soft switching. SiC-MOSFET is used to reduce the loss of reverse recovery current through the use of a high switching frequency. LDC is require large transformer and inductor because of large output current. The size of transformer and inductor can be reduced by deviding the transformer and inductor into two pieces each. This work presents the experimental results of the proposed circuit.

• 한국산업융합학회 논문집
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• 제25권3호
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• pp.451-459
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• 2022

Recently, in accordance with the demand for a large capacity of a secondary battery according to an increase in the demand for energy storage devices, a modular series battery configuration is essential. Accordingly, various cell balancing techniques have been proposed to prevent high efficiency and performance degradation of the battery. In this paper, propose a battery voltage balancing topology consisting of a flyback DC/DC converter type of a SIMO (Single-Input-Multiple Output) two-switch configuration for a series battery configuration. The proposed topology shows a structure in which a DC/DC converter connected to each module and a battery cell share one transformer. The topology cell balancing operation is a principle in which the voltage balancing converter of the battery converges to the same value through a transformer that shares a magnetic flux with the cells constituting the module through a single high-frequency transformer. In this paper, the dynamic characteristics analysis of the proposed circuit using PSIM was based and it was verified through experiments on one module.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2022년도 추계학술대회
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• pp.97-99
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• 2022

대장암의 조기 발견과 치료를 위해서는 정확한 폴립의 분할이 중요하나 다음과 같은 제약이 따른다. 개별 폴립의 위치, 크기 및 모양이 서로 상이하며, 모션 흐림 및 빛 반사와 같은 특정 상황에서 폴립과 주변 환경 간에 상당한 정도의 유사성이 존재한다. 인코더와 디코더 역할을 하는 Convolutional Neural Networks로 구성된 U-net은 이러한 한계를 극복하기 위해 다양하게 사용된다. 본 연구는 보다 정확한 폴립 분할을 위한 비전트랜스포머가 포함된 U-net 아키텍처를 제안하였고, 그 결과 제안된 방식은 표준 U-net 아키텍처보다 더 나은 성능을 보였음을 확인할 수 있었다.

• 분석과학
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• 제23권3호
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• pp.278-283
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• 2010

본 연구에서는 국제적으로 관심의 대상이 되고 있는 폴리염화비페닐류 함유 액상폐기물의 효율적인 관리를 위해 국내에서 사용되고 있는 L2000DX을 이용한 스크리닝, 신속 GC/ECD 및 기존 GC/ECD 분석방법을 절연유 15건에 적용하였다. 분석 결과 L2000DX을 이용한 경우에는 4.4~182.8 mg/L의 농도 범위로 Aroclor 1242 환산농도가 검출된 반면, 기존 GC/ECD 및 신속 GC/ECD를 이용한 분석 결과 각각 불검출~14.63 mg/L 및 불검출~13.03 mg/L로 나타났다. GC/ECD 분석방법들 간에는 약 4 mg/L이하에서 거의 차이가 없었으나, 국내의 규제농도인 2 mg/L부근의 검출농도에서는 일부 시료의 경우 기존 GC/ECD 분석결과(2.71 mg/L)에 비해 신속 GC/ECD 방법이 다소 낮은(2.49 mg/L) 측정치를 보여 국내 규제기준 2 mg/L부근에서 저평가되는 경향이 있는 것으로 나타났다.

• 전기학회논문지
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• 제63권3호
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• pp.358-366
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• 2014

This paper proposes a quasi Z-source AC-AC converter with the low DC voltage distribution capability operating as a power electronic transformer. The proposed system has configuration that the input terminals of two quasi Z-source AC-AC converters are connected in parallel, also their output terminal are connected in series. Simple control method of duty ratio was proposed for the in phase buck-boost AC voltage mode and the DC output voltage control. DSP based experiment and PSIM simulation were performed. As a result, the PSIM simulation results were same with the measured results. By controlling the duty ratio under the condition of 100 [${\Omega}$] load, quasi Z-source AC-AC converter could buck and boost the AC output voltage in phase with the AC input voltage, and the same time, the constant DC voltage could be output without affecting the AC output characteristics. And, the DC output voltage 48[V] was constantly controlled in dynamic state in case while the load is suddenly changed ($50[\Omega]{\rightarrow}100[\Omega]$). From the above result, we could know that the quasi Z-source AC-AC converter can act as a power electronic transformer with a low DC voltage distribution capability.

• 전기학회논문지
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• 제62권12호
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• pp.1678-1687
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• 2013

This paper describes a prototype of 3-phase 3.3kV/220V 6kVA modular semiconductor transformer developed in the lab for feasibility study. The developed prototype is composed of three single-phase units coupled in Y-connection. Each single-phase unit with a rating of 1.9kV/127V 2kVA consists of a high-voltage high-frequency resonant AC-DC converter, a low-voltage hybrid-switching DC-DC converter, and a low-voltage hybrid-switching DC-AC converter. Also each single-phase unit has two DSP controllers to control converter operation and to acquire monitoring data. Monitoring system was developed based on LabView by using CAN communication link between the DSP controller and PC. Through various experimental analyses it was verified that the prototype operates with proper performance under normal and sag condition. The system efficiency can be improved by adopting optimal design and replacing the IGBT switch with the SiC MOSFET switch. The developed prototype confirms a possibility to build a commercial high-voltage high-power semiconductor transformer by increasing the number of series-connected converter modules in high-voltage side and improving the performance of switching element.

• 분석과학
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• 제18권3호
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• pp.206-215
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• 2005

1929년부터 상업적으로 사용되기 시작한 폴리염화비페닐류(PCBs)는 Aroclor (미국), Kanechlor (일본), Sovol (러시아) 등 다양하게 상업적으로 시판되었다. PCBs는 209종의 동족체로 구성되어 있으며 변압기, 축전기의 절연유, 윤활유, 가소제, 도료, 복사지 등의 여러 용도로 사용되어 온 산업용 화학물질이다. 본 연구에서는 시판되는 PCBs Aroclor 제품을 구입하여, 표준물질을 사용하여 피크패턴법에 의한 정량방법과 계수비교법에 의한 정량방법을 비교하고, 시료에 적용하여 분석하였다. 분석대상 시료의 피크패턴은 Aroclor 1242:1254:1260의 세 종류가 혼합된 경우와, Aroclor 1242:1254, Aroclor 1254:1260이 혼합된 경우 그리고 Aroclor 1242, 1254 및 1260이 혼합된 시료가 다양한 비율로 검출되었다. 또한, 두 정량법에 따른 분석 결과는 혼합된 PCBs 제품의 종류가 한 종류인 경우 보다 여러 종류일수록 두 정량값의 차이가 없는 것으로 나타났다.

• 한국전기전자재료학회논문지
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• 제22권1호
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• pp.1-6
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• 2009

Air core based transformers have been designed, simulated and fabricated by using micromachining process for the application of wireless power transmission with the range of frequency from 1 GHz to 20 GHz. Fabricated transformers are the types of solenoid transformers with primary and secondary coils. the size of fabricated transformer is $1.1{\times}1.5{\sim}2.15\;mm$ including ground shield. Transformers have been measured by dividing two groups based on the turns ratio between primary coil and secondary coil which are 1:1 transformers(the number of turns of primary coil and secondary coil: 3/3, 5/5, 7/7) and l:n transformers(the number of turns of primary coil and secondary coil: 3/3, 3/6, 3/9). As a result of the measurement, the lowest insertion loss of transformers ranged from 2 dB to 2.8 dB according to the number of turns between primary coil and secondary coil. And the lowest insertion loss from the transformers was measured at the frequency from 7 GHz to 11 GHz according to the number of turns between primary coil and secondary coil. Based on the measurement data from the microfabricated transformers, the transformer with the 3/3 turns in the primary coil and secondary coil showed best performance compared to others in terms of lowest insertion loss, lowest insertion loss frequency and bandwidth.