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조준석(J.S. Cho),강병희(B.H. Kang),고재석(J.S. Gho),최규하(G.H Choe),김진흥(J.H. Kim),정석언(S.E. Chung) 전력전자학회 2001 전력전자학술대회 논문집 Vol.2001 No.7
The parallel operation system of UPS is used to increase reliability of power source at critical load. But parallel UPS system has a few defects, impedance is different from each other and circulating current occurs between UPSs, due to line impedance and parameter variation, though controlled by the same synchronization signal. According to such characteristic of parallel UPS, balanced load-sharing control is the most important technique in parallel UPS operation. In this paper, a novel power deviation compensation algorithm is proposed, it is composed of voltage controller to compensate power deviation that be calculated by using active and reactive current deviation between inverters on synchronous d-q reference frame.
장방형내 함수 다공성 물질의 동결거동에 관한 실험적 연구
김병철,김종일,김진흥,Kim, B.C.,Kim, J.I.,Kim, J.H. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.5
Freezing of saturated porous media contained in a rectangular cavity has been studied experimentally. Water and different diameter glass beads consitituted the liquid and porous media. Solidification front shape, the effects of bead diameter and initial liquid temperature was investigated. When the hot wall temperature was below $4^{\circ}C$, the freezing rate was higher at the top than at the bottom due to the density inversion, but with increasing the hot wall temperature the freezing rate at the top was effected by the liquid temperature and was lower than at the bottom. With increasing the bead diameter, the difference of freezing rate between top and bottom was increased and depends on thermal conductivity. When the liquid temperature was low in the beginning, the freezing rate was high, but with increasing the time almost the same with those of high temperature liquid.