• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.96-96
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• 2009

The purpose of this study is to clarify the transitional behavior and main factor of excessive welding distortion caused by fabrication process of STS 304 vacuum vessel having double curvature for the efficient quality control of vacuum vessel. In order to do it, the predictive equations of the welding distortion in simple weldment of vacuum vessel were established by conventional finite element analysis. And the principal factor controlling the welding distortion was identified by evaluating the welding distortion of vacuum vessel in each fabrication process with FEA and simplified thermo elastic method. Based on the results, the principal factors of distortion of vacuum vessel were clarified as angular distortion and transverse shrinkage which are a source of excessive out-of plane distortion in the double curved vacuum vessel. It was expected that the FE analysis results of this study could contribute to establish the proper control method of welding distortion for double curved vacuum vessel.

• 한국정밀공학회지
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• 제16권3호통권96호
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• pp.198-207
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• 1999

This paper presents an accurate algorithm for geometric calibration of X-ray imaging system. Calibration is a very important process for improving an imaging system performance. There has been a lot of previous works using linear camera modeling technique, where lens distortion is neglected and/or center of distortion is assumed to be known. Geometrical distortion of image intensifier, however, is very large and its center of distortion should be calculated. This paper presents a new calibration method to estimate the intensifier position and orientation, scale factor, distortion coefficient, magnification factor, and center of distortion using the least square method. We investigate the properties of the algorithm by computer simulation. Simulation results show that the parameters can be estimated accurately using the proposed algorithm.

• 전력전자학회논문지
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• 제27권2호
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• pp.134-141
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• 2022

This study presents a method for reducing current distortion that occurs when a dual-buck inverter generates reactive power. Dual-buck inverters, which are only capable of unity power factor operation, can generate reactive power capabilities by modifying a modulation technique. However, under non-unity power factor conditions, current distortion occurs at zero-crossing points of grid voltage and output current. This distortion is caused by parasitic capacitors, dead-time, and discontinuous conduction mode operation. This study proposes a modified modulation method to alleviate the current distortion at zero-crossing point of the grid voltage. A repetitive controller is applied to reduce this distortion of the output current. A 1 kVA prototype is built and tested. Simulation and experimental results demonstrate the effectiveness of the proposed method.

• 한국측량학회지
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• 제24권4호
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• pp.313-318
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• 2006

전국 규모의 연속적인 자료구조를 가진 기본지리정보의 생산 및 구축을 효율적으로 수행하기 위해서는 하나의 원점을 가진 좌표계의 도입이 요구된다. 이를 위해서 우리나라는 한반도 전역을 포괄하는 한국형 UTM 좌표계(UTM-K)를 도입하였으며, 본 연구에서는 UTM-K 좌표계에서 설정된 투영중앙 자오선 및 투영중앙 자오선의 축척계수에 대한 왜곡정도를 분석하였다. 투영왜곡의 분석을 위해서 2005년 말까지 제작된 1/25,000 수치지도들의 중심 경위도 좌표를 이용하여 투영으로 인한 축척계수를 계산하고, 이를 왜곡정도의 지표로 사용하였다. 그 결과, 현행 UTM-K에서 정의한 것을 근거로 했을 경우 지도투영으로 인한 축척계수의 누적 왜곡량은 $23.744{\times}10^{-2}$로 나타났다. 반면에 투영중앙 자오선이 $127^{\circ}\;42'$이고, 이때의 축척계수가 0.99994로 설정했을 경우 $5.1435{\times}10^{-2}$의 최소 누적 왜곡량을 보였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 하계종합학술대회 논문집(1)
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• pp.23-26
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• 2004

This paper analyzed time delay and phase distortion that generates in multipath and the degree of distortion due to power attenuation factor when UWB system is applied at indoor environment and the effects of indoor structure and material on distortion factors. Based on these distortion factors, channel model similar to actual environment is mathematically described and multipath and the degree of signal distortion generated when UWB system is applied to random environment is tested through channel model simulation and varies distortion factor that UWB system needs to consider in different indoor environment is analyzed.

• Journal of Power Electronics
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• 제15권5호
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• pp.1168-1177
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• 2015

This paper presents a scheme to improve the line current distortion of power factor corrector (PFC) topology at the zero crossing point using a predictive control algorithm in both the continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The line current in single-phase PFC topology is distorted at the zero crossing point of the input AC voltage because of the characteristic of the general proportional integral (PI) current controller. This distortion degrades the line current quality, such as the total harmonic distortion (THD) and the power factor (PF). Given the optimal duty cycle calculated by estimating the next state current in both the CCM and DCM, the proposed predictive control algorithm has a fast dynamic response and accuracy unlike the conventional PI current control method. These advantages of the proposed algorithm lower the line current distortion of PFC topology. The proposed method is verified through PSIM simulations and experimental results with 1.5 kW bridgeless PFC (BLPFC) topology.

• 조명전기설비학회논문지
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• 제12권3호
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• pp.67-73
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• 1998

본 연구에서는 기존의 정류회로가 포함하고 있는 고조파 발생과 역률저하문제를 개선하기 위한 방안으로 BPFC(Boost Power Factor Collection)방식을 사용하였다. 이 BPFC는 고역률올 구현하기 위해 가장 널리 쓰이는 방식중의 하나로서 입력전압과 거의 동둥한 지속적인 인덕터 전류를 정현파에 가까운 형태로 제어할 수 있다는 장점을 가지고 있다. 또한 BPFC는 제어방식에 의해 크게 달라질 수 었다. 본 논문에서는 순간모드선택 피크 전류제어방식과 PWM 평균전류 재어방식을 이용한 고역률 저고조파를 갖는 정류회로를 구성하여 각각에 대하여 비교분석하였다.

• Journal of Power Electronics
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• 제15권1호
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• pp.10-17
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• 2015

A quasi-constant on-time controlled buck front end in combined discontinuous conduction mode and boundary conduction mode is proposed to improve power factor (PF).When instantaneous AC input voltage is lower than the output bus voltage per period, the buck converter turns into buck-boost converter with the addition of a level comparator to compare input voltage and output voltage. The gate drive voltage is provided by an additional oscillator during distortion time to eliminate the cross-over distortion of the input current. This high PF comes from the avoidance of the input current distortion, thereby enabling energy to be delivered constantly. This paper presents a series analysis of controlling techniques and efficiency, PF, and total harmonic distortion. A comparison in terms of efficiency and PF between the proposed converter and a previous work is performed. The specifications of the converter include the following: input AC voltage is from 90V to 264V, output DC voltage is 80V, and output power is 94W.This converter can achieve PF of 98.74% and efficiency of 97.21% in 220V AC input voltage process.

• Journal of Welding and Joining
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• 제31권5호
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• pp.7-14
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• 2013

The legitimacy of dominating factor in the high accuracy prediction of welding distortion was investigated for butt welding and fillet welding. When out-of-plane distortion was measured by the experiment objecting to butt welding, if tack welding was easily performed, the position of a neutral axis was variously changed by the irregularity. Then, there have been a case that out-of-plane distortion was generated in the unexpected direction. This case should be especially noted. New model for the experiment was proposed so as to solve this problem. As it was elucidated by the case of fillet welding, it was verified that the analysis should be carried out with satisfying the yield condition (especially at high temperature above 700 degree Celsius) and with closely simulating the penetration shape (heat input in weld metal) in order to solve the proposition that is the high accuracy prediction of welding distortion. It was confirmed that residual stress is highly predicted because welding distortion is highly predicted, too.

• Journal of Welding and Joining
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• 제28권5호
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• pp.64-68
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• 2010

The purpose of this study is to develop the control technology of global distortion in the deck of superstructures during manufacturing processes. The behavior of global distortion in the deck was evaluated by FEA and verified through comparing with the measured results by 3D measuring instrument. It was seen from the results that the principal factor inducing the global distortion is to be the bending moment associated with the longitudinal shrinkage force and transverse shrinkage caused by welding of stiffeners and flame heating to correct the excessive local out-of-plane distortion. Based on the results, the amount of reverse distortion in the thin deck plate was determined to control the global distortion in the deck plate. The proposed distortion control technology was verified by applying it to the actual structure.