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섬유배향각 분포측정에 있어서 농도법의 정밀도에 미치는 섬유종횡비와 면적비의 영향
이상동,김혁,이동기,한길영,김이곤,Lee, S.D.,Kim, H.,Lee, D.G.,Han, G.Y.,Kim, E.G. 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.4
To investigate accuracy of intensity method for measurement of the fiber orientation distribution, fiber orientation function is calculated by drawing simulation figures for the fiber orientation as varying fiber aspect ratio, fiber area ratio, and fiber orientation state, respectively. The values of fiber orientation function measured by intensity method are compared with the calculated values of fiber orientation function. The results show that measurement accuracy of the fiber orientation angle distribution by intensity method is affected by the fiber aspect ratio when the total length of oriented fiber is same. The average gradient of fiber orientation function is 0.94 for 1000mm of the total fiber length and is 0.93 for 2000 mm when the fiber aspect ratio is over 50. Measurement accuracy by intensity method is about 94% and the reliable data can be obtained by intensity method.
이현원(H.W.Lee),최세경(S.K.CHOI),김명찬(M.C.KIM),이선재(S.J.LEE),이상동(S.D.LEE) 전력전자학회 1999 전력전자학술대회 논문집 Vol.- No.-
The three level circuit systems are able to reduce harmonic currents without requiring high frequency switching to the devices, and are suitable for high voltage, large capacity systems. However the three level circuit system has a problem that the mid point potential varies when the current flows into or out of the mid point. the variation causes voltage deviation in the DC waveforms as well as unbalanced voltage stress to the switching devices therefore the variation should be suppressed.<br/> In this paper we have proposed a new kind of PWM method for three level circuit system based on the change of phase PWM reference value with the ability to suppress the mid point voltage variation. The new method is easily implemented without complicated calculation and it's performance is similar to space vector modulation. The validity of the proposed method is verified by computer simulation