• 전기학회논문지
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• 제66권9호
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• pp.1437-1443
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• 2017

Electric energy is consumed or regenerated according to an operation of electric rail cars in urban railway power substations. A thyristor dual converter system is used to deal with the electric energy. Since the AC input voltage of power substations is $22.9kV{\pm}10%$, the magnitude of the AC voltage fluctuates according to load conditions, so the secondary side voltage of the DDY transformer also fluctuates. In the thyristor dual converter, the response characteristics of the DC output voltage and the DC output current are changed based on an initial firing angle in the cross mode conversion between the forward mode and the reverse mode. Therefore, this paper proposes the initial firing angle tracking algorithm considering fluctuation of the AC input voltage. The effectiveness of the proposed algorithm is verified by a simulation compared with the conventional algorithm.

• KIEE International Transactions on Electrophysics and Applications
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• 제2C권6호
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• pp.304-308
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• 2002

We demonstrate a simple pulsed $CO_2$ laser with millisecond long pulse duration in a tube at a low pressure of less than 30 Torr. The novel power supply for our laser system switches the voltage of the AC power line (60Hz) directly. The power supply doesn't need elements such as a rectifier bridge, energy-storage capacitors, or a current-limiting resistor in the discharge circuit. To control the laser output power, the pulse repetition rate is adjusted up to 60Hz and the firing angle of SCR(Silicon Controlled Rectifier) gate is varied from 30。 to 150。. A ZCS (Zero Crossing Switch) circuit and a PIC one-chip microprocessor are used to control precisely the gate signal of the SCR. The maximum laser output of 35 W is obtained at a total pressure of 18 Torr, a pulse repetition rate of 60 Hz, and a SCR gate firing angle of 90。 . In addition, the resulting laser pulse width is approximately 3㎳(FWHM). This is a relatively long pulse width, compared with other repetitively pulsed $CO_2$ lasers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2138-2139
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• 2005

We demonstrate a simple CO2 laser by controlling firing angle of a TRIAC switch in ac power line. The power supply for our laser system switches the voltage of the AC power line (60Hz) directly. The power supply does not need elements such as a rectifier bridge, energy-storage capacitors, or a current-limiting resistor in the discharge circuit. In order to control the laser output power, the pulse repetition rate is adjusted up to 60Hz and the firing angle of TRIAC gate is varied from 45 to 135. A ZCS(Zero Crossing Switch) circuit and a PIC one-chip microprocessor are used to control the gate signal of the TRIAC precisely. The maximum laser output of 40W is obtained at a total pressure of 18Torr, a pulse repetition rate of 60Hz, and a TRAIC gate firing angle of 90.

• ETRI Journal
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• 제6권4호
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• pp.37-40
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• 1984

in the case of using SMES to shave the peak load with the isolated synchronous ge nerator- converter, the performance equations are derived. The commutation angle, the power angle, the field current, the storage energy and the power are derived by changing firing angle, that is, following the excitation velocity of SMES current. The output characteristics are computed by digital computer simulation.

• 전력전자학회논문지
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• 제9권6호
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• pp.584-591
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• 2004

기존의 아날로그 점호각 제어방법은 op-amp, 저항 및 커패시터 등을 사용하였기 때문에 아날로그 회로의 특성상 온도와 소자의 경년변화에 따라 파라메타 값이 변동하며 전원전압의 노이즈에 민감하게 반응하는 단점이 있었다. 따라서 본 논문에서는 디지털 사이리스터 점호회로를 이용하여 기존의 아날로그 점호회로 장점인 선형특성, 그리고 전원전압 노이즈 온도 및 갱년변화에 의한 수동소자의 변동에 강인한 특징을 갖는다. 또한 디지털 시스템의 장점인 연산기능을 이용하여 전원전압의 불평형 발생시 디지털 시스템의 특징인 연산기능을 이용하여 전원전압의 불평형을 검지하고 보상알고리즘을 도입하여 언제나 리플이 없는 출력전압을 만들어내어 사이리스터 전력변환 시스템의 안정적인 운전이 가능하게 할 수 있는 장점이 있다.

• Tribology and Lubricants
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• 제35권4호
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• pp.244-266
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• 2019

The purpose of this study is to estimate the wear volumes of engine journal bearings operating at variable angular velocity of a shaft in the beginning of firing start-up cycle. To do this, first we find the potential region of wear scar on engine journal bearings where the applied bearing load and crank shaft velocity are variable. The potential wear regions are discovered by finding minimum oil film thickness at every crank angle existing below most oil film thickness scaring wear (MOFTSW) obtained based on the concept of the centerline average surface roughness. Then we calculate the wear volume from the wear depth and two wear angles decided by the magnitude of each film thickness lower than MOFTSW at every crank angle. The results show that the expected wear region is located at a few bearing angles after and/or behind the upper center of a big-end bearing and the lower center of a main bearing. And the real wear region is similar to the estimated wear region. Further we find that the wear scar on an engine journal bearing may occur at re-starting time after switch-off of a start motor especially under the condition of high oil temperature.

• 전력전자학회논문지
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• 제5권1호
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• pp.54-62
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• 2000

본 논문은 Vernier 모드에서 운전하는 2-모듈 TCSC로 구성된 전력송전시스템의 특성 해석을 위하여 싸이리스터 점호각 계산을 푸리에 공간에서 수행한다. 이를 위하여 싸이리스터 스위칭 함수를 이용하여 TCSC 리액터 전류에 관한 연립방정식을 구하였다. TCSC 모듈의 등가 임피던스가 전력송전 시스템이 요구하는 특정값을 갖게 하는 싸이리스터 점호각을 수치해석 방법을 사용하여 구하고, TCSC 전력송전시스템의 정상상태 특성을 해석하였다. 또한 EMTP 시뮬레이션을 수행하여 푸리에 공간에서의 점호각 계산의 타당성을 시평면상에서 검증하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.550-552
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• 1997

This paper describes a detailed performance analysis of TCSC using experiment with a scaled model. A 3-phase scaled model of TCSC was built with rating of 2kVA to verify the operation. The variable reactance of TCSC with respect to the firing angle of thyristor switch analyzed theoretically and experimentally. And the limit of TCSC operation was investigated in whole range of the thyristor firing-angle. The experimental results with scaled model were compared with the simulation results for a periodic state space model using MATLAB.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(I)
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• pp.779-781
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• 1987

In phase controlled rectifier(PCR), harmonica are changed according to the variation of a firing angle. These harmonics are supplied with the input of the inverter. And then, inverter output comes about the harmonics combined with the switching frequency of the inverter. Hence the efficiency of the induction motor ia decreased by the harmonic of the inverter output. In this paper, it analyzed about an effect of these harmonics ia analyzed by a computer simulation. The total harmonic distortion (THD) in the case of PCR containing the ripple was considerably larger than THO of the DC source. Therefore, it was proved that the firing angle variation of PCR had to be limited.

• Tribology and Lubricants
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• 제34권4호
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• pp.146-159
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• 2018

This paper presents a wear analysis procedure for calculating the wear of journal bearings of a four-strokes and four-cylinder engine operating at a constant angular crank shaft speed during firing conditions. To decide whether the lubrication state of a journal bearing is in the possible region of wear scar, we utilize the concept of the centerline average surface roughness to define the most oil film thickness scarring wear (MOFTSW) on two rough surfaces. The wear volume is calculated from the wear depth and wear angle, determined by the magnitude of each film thickness on a set of oil films with thicknesses lower than the MOFTSW at every crank angle. To calculate the wear volume at one contact, the wear range ratio during one cycle is used. The total wear volume is then determined by accumulating the wear volume at every contact. The fractional film defect coefficient, asperity load sharing factor, and modified specific wear rate for the application of the mixed-elasto-hydrodynamic lubrication regime are used. The results of this study show that wear occurs only at the connecting-rod big-end bearing. Thus, simulation results of only the big-end bearing are illustrated and analyzed. It is shown that the wear volume of each wear scar group occurs consecutively as the crank angle changes, resulting in the total accumulated wear volume.