• 전력전자학회논문지
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• 제10권5호
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• pp.450-456
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• 2005

본 논문에서는 새로운 이중접속 방식의 60-스텝 인버터를 제안하고 이를 이용한 대용량 STATCOM에 관하여 동작원리 및 제어방식을 기술하기로 한다. 기존의 12-스텝 인버터에 간단한 보조회로를 추가하여 출력전압의 파형을 60-스텝으로 개선하였다 제안한 방식의 인버터는 커패시터의 전압분할이 필요하지 않아 간접제어 방식의 적용이 용이하며 $10Mvar\~30Mvar$급 범위의 STATCOM에 적용하면 경제적이다. 2KVA급 시작품의 실험결과로부터 제안한 방식의 타당성을 입증하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1634-1636
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• 2001

We have developed the global assessment system for medium voltage power cable systems. Our purpose of diagnostic activity is the economic discrimination and maintenance of bad cables which is likely to cause cable system failure. We have atapted the Voltage Decay Method to construct the power cable assessment system for our diagnostic purpose. From the field application test results, we have concluded that our system is successful and convenient for the discrimination and maintenance of the damaged cables economically.

• 한국정보통신학회논문지
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• 제13권5호
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• pp.922-930
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• 2009

유도 전동기를 전압 제어하기 위한 최적 PWM 스위칭 방법을 제시하려한다. 전압 인버터의 공간 벡터 변조 방식은 DC-버스 이용을 향상시키고 정류 손실을 감소시키기 때문에 디지털 구현의 경우 특히 선호하는 PWM 방법이다. 유도 전동기 전압 제어를 위한 최적 PWM 스위칭 방법은 제시한 최적 PWM 알고리즘을 사용하여 두 개의 활성 전압 벡터(active voltage vector)와 하나의 영 전압 벡터(zero voltage vector)로 구성하였다. 선택된 스위칭 순차 열은 변조 지수(modulation index)와 운송파(carrier wave) 주기의 함수로 정의 된다. 순차 열은 인버터 스위칭 손실과 전류 리플 값을 기준으로 사용하여 선택된다. 실험 결과 중 저 전력용으로 사용할 경우 스위칭 주파수를 증가시킴에 따라 고조파 왜곡이 감소하고 동특성이 좋아짐을 확인할 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제8권2호
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• pp.304-315
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• 2013

In this paper, analysis of cascaded H-bridge multilevel inverter in DTC-SVM (Direct Torque Control-Space Vector Modulation) based induction motor drive for FCEV (Fuel Cell Electric Vehicle) is presented. Cascaded H-bridge multilevel inverter uses multiple series units of H-bridge power cells to achieve medium-voltage operation and low harmonic distortion. In FCEV, a fuel cell stack is used as the major source of electric power moreover the battery and/or ultra-capacitor is used to assist the fuel cell. These sources are suitable for utilizing in cascaded H-bridge multilevel inverter. The drive control strategy is based on DTC-SVM technique. In this scheme, first, stator voltage vector is calculated and then realized by SVM method. Contribution of multilevel inverter to the DTC-SVM scheme is led to achieve high performance motor drive. Simulations are carried out in Matlab-Simulink. Five-level and nine-level inverters are applied in 3hp FCEV induction motor drive for analysis the multilevel inverter. Each H-bridge is implemented using one fuel cell and battery. Good dynamic control and low ripple in the torque and the flux as well as distortion decrease in voltage and current profiles, demonstrate the great performance of multilevel inverter in DTC-SVM induction motor drive for vehicle application.

• 한국재료학회지
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• 제8권10호
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• pp.961-968
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• 1998

상변화형 광디스크의 보호막으로 사용되는 $ZnS-SiO_2$ 유전체막을 RF magnetron 스퍼트링방법에 의하여 제조하는 경우에 기판 바이어스전압의 영향을 조사하기 위하여, 알곤가스 분위기에서 ZnS(80mol%)-$SiO_2$(20mol%)타겟을 사용하여 Si Wafer와 Corning flass 위에 박막을 증착시켰다. 본 실험에서는 여러 실험 변수를 효과적으로 조절하면서 실험의 양을 줄이고 도시의 산포를 동시에 만족시키는 최적조건으로 타겟 RF 출력 200W, 기판 RF 출력 20W, 아르곤 압력 5mTorr과 증착시간 20분을 얻을 수 있었으며, 신뢰구간 95%에서 확인실험을 수행하였다. 증착된 박막의 열적 저항성을 측정하기 위해 $300^{\circ}C$와 $600^{\circ}C$에서 열처리시험을 수행하였고, Spectroscopic Ellipsometry 측정을 통한 광학적 데이터를 바탕으로 Bruggeman EMA(Effective Medium Approximation)방법을 이용하여 기공(void)분률을 측정하였다. 본 연구결과에 의하면 특성치 굴절률에 대하여 기판 바이어스인자와 증착시간 사이에는 서로 교호작용이 강하게 존재함을 확인할 수 있었다. TEM분석과 XRD 분석 결과에 의하면 기판 바이어스를 가한 최적조건에서 증착된 미세조직은 기존의 바이어스를 가하지 않을 조건에서 증착시킨 박막보다 미세한 구조를 가지며, 또한 과도한 바이어스전압은 결정구조의 조대화를 야기시켰다. 그리고 적절한 바이어스전압은 박막의 밀도를 증가시키며, 기공분률을 약 3.7%정도 감소시킴을 확인할 수 있었다.

• 대한전기학회논문지
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• 제37권12호
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• pp.872-878
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• 1988

During the past few years, a great deal of attention has been directed to the application of superconductivity to the electrical systems such as superconducting power transmission lines, superconducting magnet energy storage and so on. Yet in order to develop the practical model of these electrical equiqments utilizing suprconductivety and other phenomena at cryogenic temperautre, it is necessary to know the dielectric behaviour of insulating materials at cryogenic temperature in view of reliability, safety and economy of these machines. Investigation of dielectric properties of cryogenic liquids is very important due to the dual role of those as the dielectric and cooling medium. In this study, we investigated results measured over several kinds of dielectric characteristics of liquid nitrogen taking into consideration for application of high Tc superconductor. Dependence of breakdown voltage of gap width, polarity and pressure is reported in this paper and time delay characteristics of breakdown is also the subject of this discussion.

• Journal of Welding and Joining
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• 제21권1호
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• pp.48-53
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• 2003

The object of this study is to examine the effect of short circuit time ratio (SCTR) and current rise delay time (Td) on the spatter generation at low and medium current range in $CO_2$ welding. The spatter was evaluated by the weight generated in the welding of bead-on-plate for 30 seconds (3 times). Td was varied by order of 0, 0.4, 0.8 and 1.2 msec. At each Td, the short circuit time ratio was varied by the output voltage of the welding power source. In the low current range, it was found that the optimum SCTR was 20~25%, and the minimum spatter generation weight was obtained in the case of Td=0.4msec and SCTR=22% even though the remarkable difference was not showed by the application of Td. In the medium current range, it was confirmed that the arc was stable though the SCTR was increased from 20% to 40% by the control of current wave. Spatter generation weight depended on the variation of Td, and the lowest value of spatter generation weight occurred at Td=0.8~1.2msec.

• Geomechanics and Engineering
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• 제18권5호
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• pp.527-534
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• 2019

Although ground investigation had carried out prior to the construction, many problems have arisen during the civil-engineering works because of the presence of the unexpected underground utility lines or anomalies. In this study, a new geophysical exploration method was developed to solve those problems by improving and supplementing the existing methods. This new method was based on the difference of electrical resistance values between anomalies and surrounding ground medium. A theoretical expression was suggested to define the characteristics of the anomalies such as location, size and direction, by applying the electric field analysis. An inverse analysis algorithm was also developed to solve the theoretical expression using the measured electrical resistance values which were generated by the voltage flowing the subsurface medium. To verify the developed method, field applications were conducted at the sites under construction or planned. From the results of the field tests, it was found that not only the new method was more predictive than the existing methods, but its results were good agreed with the measured ones. Therefore, it is expected that application of the new exploration method reduces the unexpected accidents caused by the underground uncertainties during the underground construction works.

• 한국정밀공학회지
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• 제27권4호
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• pp.14-19
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• 2010

In this paper, using interleaved power factor correction how to improve the inverter efficiency studied. Interleaved method can reduce the conduction losses and the inductor energy. Generally, critical conduction mode (CRM) boost PFC converter used low power level because of the high peak currents. if you use the interleaved mode, CRM PFC can be used medium or high power application. interleaved CRM PFC can reduce current ripple for higher system reliability and size of buck capacitor and EMI filter size. Interleaved CRM PFC that is installed in front of inverter can maintain the constant voltage regardless of the input voltage.

• 산업기술연구
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• 제27권B호
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• pp.91-96
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• 2007

Electrical impedance tomography (EIT) is a technique for determining the electrical conductivity and permittivity distribution within the interior of a body from measurements made on its surface. One recent application area of the EIT is the detection of breast cancer by imaging the conductivity and permittivity distribution inside the breast. The present standard for breast cancer detection is X-ray mammography, and it is desirable that EIT and X-ray mammography use the same geometry. A forward model of a simplified mammography geometry for EIT imaging was proposed earlier. In this paper, we propose an iterative algorithm for computing the current pattern that will be applied to the electrodes. The current pattern applied to the electrodes influences the voltages measured on the electrodes. Since the measured voltage data is going to be used in the impedance imaging computation, it is desirable to apply currents that result in the largest possible voltage signal. We compute the eigenfunctions for a homogenous medium that will be applied as current patterns to the electrodes. The algorithm for the computation of the eigenfunctions is presented. The convergence of the algorithm is shown by computing the eigencurrent of the simplified mammography geometry.