A Feeder Impedance Identification Based Droop Control Method for Accurate Reactive Power Sharing in Islanded Microgrids

Jianyong Zhao,Jian Li,Heng Nian,Lei Yang,Bao Gai,Zaiping Pan,Yourui Xu 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Due to the unmatched feeder impedance, the conventional voltage and frequency droop control method is unable to accurately allocate the output reactive power of DG units in proportion to their power ratings. To solve this issue, this paper has proposed a feeder impedance identification based droop control method. Firstly, the relationship among the reactive power sharing, reactive power droop slope and feeder impedance in islanded microgrids is illustrated. An online feeder impedance identification method is subsequently adopted to modify the reactive power droop slope of DG unit. In this way, the effect of unmatched feeder impedance on reactive power sharing is eliminated without communication among DG units. Experimental results implemented on an islanded microgrid apparatus have validated the feasibility of the proposed droop control method.

Multi-scale Nano/Micro Fiber Scaffolds with Different Topological Morphologies

Jianyong Feng,Ruixiang Xu,Jiaming Zhao,Lingxiao Zhang 한국섬유공학회 2022 Fibers and polymers Vol.23 No.4

The multi-scale fiber and topological morphologies had been shown to influence cell mitogenesis and chemotaxis,direct cell differentiation, and induce constructive host tissue remodeling responses. To simulate multi-layer meshworkarchitecture of extracellular matrix and regulate cell behavior, we prepared different topological scaffolds, such as 3Dprinting fiber scaffolds, poly(lactic acid) (PLA) electrospun fiber scaffolds, 3D printing/knitted fabric composite scaffolds,and PLA electrospinning/knitted fabric composite scaffolds. The surface morphology, pore diameter, thickness, stress-straincurve, electrical current, and other properties were studied. The aim is to prepare multi-scale nano/micro fiber scaffolds withdifferent topological morphologies and properties that can provide structural and mechanical support for potential tissueengineering applications.

Thermal analysis for the large precision EDM machine tool considering the spark energy during long-time processing

Zhaoxi Zhao,Yukui Wang,Zhen-long Wang,Jianyong Liu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.2

Thermal error is a major factor influencing the accuracy of large precision electrical discharge machining (EDM) machine tools, especially when processing continuously for a long time. In this paper, a novel thermal analysis model was set up to identify the static and dynamic thermal behaviour of the large EDM machine tool. The thermal effect of multiple spark discharges is considered. An equivalent heat flux method was proposed to model the intermittent heat flux for the first time. Both the steady and transient analyses were applied to investigate the thermal equilibrium time of critical points. It is found that when the study point is far away from the heat source, the longer thermal equilibrium time is needed. And the thermal equilibrium time of the machine tool was also estimated. Verification experiment has been performed, indicating the simulation accuracy of 87 % on the temperature rise of the electrode. Moreover, on the displacement of the spindle, the simulated result matched with the experimental result in Z direction error of 7 %. Finally, suggestions for reducing the thermal deformation were proposed to further improve the machining accuracy of large EDM machine tools.

Dynamic thermal behavior and thermal error prediction of spindle due to periodic jump motions in a large precision die-sinking EDM machine

Zhaoxi Zhao,Jia Zhang,Yukui Wang,Zhen-long Wang,Jianyong Liu,Chenghao Quan 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.7

Thermal error which has been widely studied in cutting machine tools, was ignored in the EDM machines in most cases, since there is usually no high-speed rotation for spindles. However, for large die-sinking EDM machines, due to heavy load of drive system and long processing cycle of large aeronautical parts, thermal error induced by jump motion has seriously impaired the machining accuracy and gradually been recognized. In this paper, the dynamic thermal behavior of spindle induced by periodic jump motions in large precision die-sinking EDM machine was studied for the first time. Noted that the Z-axis base and column show obvious temperature rise and the thermal error in Y direction is the largest, which is about 6.5 and 5 times compared with that in X and Z directions. Based on this, an efficient thermal error prediction model was presented. Thermal sensitive points were picked out through fuzzy clustering and correlation theory, taken as inputs of radial basis function (RBF) neural network to guarantee the accuracy. As a result, the prediction accuracy in X, Y and Z directions are 95.2 %, 92.5 % and 94.4 %, respectively. Finally, the effect of jump period on spindle thermal behavior was investigated, and suggestions for optimizing jump motion parameters were proposed to further improve the machining accuracy of large EDM machines.

Large and moderate deviation principles for the bootstrap sample quantile

Yu Miao,Jianyong Mu,Jinghuan Zhao,Saralees Nadarajah 한국통계학회 2017 Journal of the Korean Statistical Society Vol.46 No.4

Let {X, Xn, n ≥ 1} be a sequence of independent identically distributed (i.i.d.) random variables defined on a probability space (Ω, F , P) with common distribution F , and let {X∗ n,1, · · · , X∗ n,n} be a bootstrap sample from the empirical distribution Fn. Based on the bootstrap sample, the moderate deviation, large deviation and Bahadur’s asymptotic efficiency of the bootstrap sample pth quantileξ ∗ np are established.

A New Modified Method to Obtain a High Melt Index of PLA Polymer and Preparation of Melt-Blown Nonwoven Cloth

Qian Lin,Jianyong Feng,Lixia Zhao 한국섬유공학회 2023 Fibers and polymers Vol.24 No.10

Due to the low melt index of polylactic acid (PLA) polymer, it is difficult to melt-blown processing. Here, a new modified method to obtain a high melt index of PLA polymer and melt-blown nonwoven cloth was studied. PLA polymers are modified by the thermally degraded method of stannous octoate (Sn(Oct)2) and polyethylene glycol (PEG) to obtain a high melt index (1054 g/10 min) in comparison with a low melt index (23 g/10 min) of original unmodified PLA polymer. The fiber of modified PLA polymer melt-blown cloth is obviously thinner, having sub-micron fibers, the smallest fiber is about 200 nm. From our test, modified PLA polymer melt-blown cloth has good oil absorption, oil–water separation, and potential air filtration property. In terms of degradation, the modified PLA polymer melt-blown cloth showed excellent degradation performance in basic aqueous solutions at 55 °C at pH 12, reaching a degradation rate of around 95% at 60 h.

Experimental Study on the Pipe-Soil Interface under the Influence of Pipe Jacking Stagnation Time

Tianliang Li,Wen Zhao,Run Liu,Jianyong Han,Cheng Cheng 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.3

In the process of long-distance and large-diameter pipe jacking, thixotropic mud is generally injected into the outer surface of the pipe wall to reduce the frictional resistance between the pipe and the soil. The process of pipe jacking may be stopped due to various reasons such as pipe rupture and equipment damage. When the pipe is restarted after being stopped for a period of time, the interface mechanical properties usually change substantially, resulting in a substantial increase in frictional resistance compared to before the stop. However, the mechanical properties and shear mechanism of the pipe-soil interface after jacking is restarted have not been sufficiently investigated. In this paper, a series of gravelly sand-concrete direct shear tests are carried out, in which lubricant is injected into the interface between gravelly sand and concrete, and the effect of construction stagnation time is considered. The mechanical properties of the interface when the concrete pipe is restarted after stagnation is studied by the direct shear tests. The results show that the friction coefficient of pipe-soil interface increases with the stagnation time, which is determined by the thixotropic mud state and the content of gravelly sand involved in shear. In a short period of stagnation, the friction coefficient is determined by the cohesion caused by thixotropic mud and the friction angle produced by the gravelly sand involved in the shearing action. With the increase of stagnation time, the friction angle gradually becomes the decisive factor for the increase of friction coefficient.

Preparation and Characterization of PLA Film/3D Printing Composite Scaffold for Tissue Engineering Application

Chenjie Meng,Jiaming Zhao,Yuxiang Yin,Jun Luo,Lianying Zhao,Wenbin Jiang,Jianyong Feng 한국섬유공학회 2020 Fibers and polymers Vol.21 No.4

Three-dimensional (3D) printing technology provides an effective alternative for tissue engineering scaffold. Inthis paper, a composite scaffold composed of polylactic acid (PLA) film and 3D printing scaffold was fabricated which couldprovide structural and mechanical support for tissue application. The effects of PLA film/3D printing composite scaffold onscaffold morphology, average diameter, pore diameter, mechanical properties, themal conductivity, electrical conductivity,and surface hydrophilicity were characterized. PLA film/3D printing composite scaffold had larger thickness, bettermechanical and thermal conductivity properties in comparison with pure PLA film and 3D printed scaffold. These resultssuggested that composite scaffold with relatively good overall performance could be a potential candidate for tissueengineering application.

Calculating Jacking Forces for Circular Pipes with Welding Flange Slabs from a Combined Theory and Case Study

Pengjiao Jia,Baofeng Jiang,Wen Zhao,Yongping Guan,Jianyong Han,Cheng Cheng 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.4

Recently, the Steel Tube Slab (STS) curtain method has been successfully used in the construction of ultra-shallow metro stations in modern urban areas. By using the STS curtain method, the external surfaces of pipes are welded with flange slabs, and then the pipes are jacked into soils. However, the nature and extent of the influence of flange slabs on the calculation of jacking force is unclear. This paper presents the first combined theoretical and case study to calculate the increase of jacking forces for circular steel pipes with welded flange slabs during the entire jacking process. The increase of jacking forces was assumed to balance the friction at the soil-pipeline interface. Theoretical formulae were firstly developed to calculate earth pressure based on pressure arch theory and elastic foundation beam theory. A case study was then performed to verify the theoretical results with the field data from Olympic Metro Station on the Shenyang Metro Line 9 in China. Subsequently, factors influencing the calculation of jacking force were analyzed and discussed. Results show that the theoretical formulae produced good results with minor errors. The implications of these findings regarding the prediction of jacking force and selection of hydraulic jack are discussed.

A new terpene coumarin microbial transformed by Mucor polymorphosporus induces apoptosis of human gastric cancer cell line MGC-803

Guangzhi Li,Junchi Wang,Xiaojin Li,Jianguo Xu,Zhao Zhang,Jianyong Si 대한약학회 2018 Archives of Pharmacal Research Vol.41 No.6

20-Z auraptene (1) is a synthesized monoterpenecoumarin with anticancer activity against human gastriccancer cells. In order to find new potential anticancer agent,Mucor polymorphosporus was used to transform cis-auraptene. Four new terpene coumarins with notable changesin the skeletal backbone, 20-Z auraptene A-D (2–5), wereobtained and evaluated for their antiproliferative effectsagainst human normal gastric epithelium cells and humangastric cancer cells. These new compounds showed selectivecytotoxic activity against MGC-803 cells with IC50values from 0.78 ± 0.13 to 10.78 ± 1.83 lM and thetherapeutic index could also be significantly improved(TI = 59.0) compared with that of 1 (TI = 5.5). Thestructures of these metabolites were elucidated throughextensive spectroscopic methods, and the possible biotransformationpathway of 1 by Mucor polymorphosporuswas also proposed. Furthermore, the mechanism of theantiproliferative effects against MGC-803 cells of the mostpotent compound, 20-Z auraptene A (2), was characterized. Annexin V/PI staining and abnormal expression of apoptosis-related protein suggested that compound 2 inducesapoptosis in gastric cancer MGC-803 cells. Therefore, it ispossible that compound 2 has the potential to be applied ingastric cancer therapy.