Performance Improvement Strategy for Parallel-operated Virtual Synchronous Generators in Microgrids

Zhang, Hui,Zhang, Ruixue,Sun, Kai,Feng, Wei The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.2

The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

Effect of Bypass Ratio on Optimal Fan Outer Pressure Ratio and Performance for Turbofan Engines

Ruixue Zhang,Jun Jiang,Anthony Jackson 한국항공우주학회 2019 International Journal of Aeronautical and Space Sc Vol.20 No.1

This study was carried out to explore the effect of bypass ratio on optimal fan outer pressure ratio and the performance of turbofan engine with the same engine core. The member of Rolls-Royce Trent family, Trent-XWB, is chosen as the baseline engine. Based on the published data, a model for the simulation of engine performance was set up. Then, a series of engine models with different bypass ratios were established based on the same Trent-XWB engine core and the way to get optimal fan outer pressure ratio was derived. It was concluded that for the fixed engine core, when the bypass ratio was chosen, there would be one optimal outer pressure ratio existing which could make the thrust maximum and the specific fuel consumption reach minimum. By comparing the performance of the turbofan engines with different bypass ratios, it shows that the increase of bypass ratio results in higher thrust and lower specific fuel consumption. However, the additional cost like the increase of both drag and weight needs to be taken into account at the preliminary design stage in practice.

Performance Improvement Strategy for Parallel-operated Virtual Synchronous Generators in Microgrids

Hui Zhang,Ruixue Zhang,Kai Sun,Wei Feng 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.2

The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG’s controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

Effect of CeO2 addition on crystallization and thermophysical properties of Li2O-ZnO-SiO2 glass-ceramics

Ruixue Li,Qian Zhang,Xingliang Peng,Weizhen Liu 한양대학교 세라믹연구소 2020 Journal of Ceramic Processing Research Vol.21 No.1

The effect of CeO2 addition on crystallization and thermo-physical properties of lithium zinc silicate (LZS) glasses containingLi2O-ZnO-SiO2-Al2O3-Na2O-P2O5 was investigated. The changes of CeO2 contents (2-8 wt.%) had an obvious influence on thetransition temperatures (Tg) and crystallization temperatures (Tc) of LZS glass-ceramics, and they increased with CeO2 contentincreasing. According to XRD analysis, CeO2 promoted the formation of cristobalite and β-spodumene crystals, and β-spodumene increased obviously. As the CeO2 content increasing, the microstructure and microhardness (being 6.88 Gpa at 880oC) of glass-ceramics had great changes. The average thermal expansion coefficient (20 - 450 oC) showed first increasing thendecreasing, having a wide range. The maximum of thermal expansion coefficient was obtained when the glass-ceramicscontained 4 wt.% CeO2, being 175×10−7 K−1 (at 700 oC) and 178×10−7 K−1 (at 880 oC) respectively. Excellent thermo-physicalproperties indicate the glass has greater potential application, such as being used as sealing glass.

Polyacrylonitrile mesoporous composite membranes with high separation efficiency prepared by fast freeze-extraction process

Ruixue Lv,Faizal Soyekwo,Qiugen Zhang,Runsheng Gao,Jianyang Wu,Yan Qu,Aimei Zhu,Qinglin Liu 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.49 No.-

Polymer mesoporous membranes are widely employed in many membrane processes includingultrafiltration and dialysis, and become more crucial with increasing demand in chemical and lifefields. Here we report a highly-efficient polymer membrane with sub-5 nm pores and highflux frompolyacrylonitrile (PAN) nanoparticles produced from dilute PAN solution via fast freeze-extractionprocess. The25 nm-size PAN nanoparticles forming brad-like chains are dispersed in ethanol solutionand used to prepare the membrane byfiltration-assisted assembly method across a macroporoussupport. Effects of solvents and usage of PAN on membrane formation is studied in detail. The resultantmembranes comprise of the nanoparticles stacked on the support to form a mesoporous separation layerwith a controllable thickness and a cut-off of below 5 nm. They exhibit excellent separation performancesin ultrafiltration of protein and nanoparticle solutions. Typically, the membrane with 94.6% rejection of5 nm gold nanoparticles has a pure waterflux of 823 L m 1 h 1 bar 1 and perfect rejection for ferritinmolecules and 10 nm gold nanoparticles. The newly developed membranes should have wide applicationin chemical, environment and lifefields.

Purple Sweet Potato (Ipomoea batatas L.) Color Alleviates High-fat-diet-induced Obesity in SD Rat by Mediating Leptin’s Effect and Attenuating Oxidative Stress

Yi Zhang,FuXiang Niu,Jian Sun,Fei Xu,RuiXue Yue 한국식품과학회 2015 Food Science and Biotechnology Vol.24 No.4

Obesity and associated diseases are world-wide problems. The preventive effect of purple sweet potato color (PSPC) on high fat diet (HFD) induced obesity was investigated along with the mechanism underlying the effect. Eight-week-old male Sprague Dawley strain rats were grouped into 7 groups and intragastrically administered PSPC once a day. Obesity was prevented and abnormal glucose, triglyceride, and total cholesterol levels induced by the HFD for 6 weeks were restored to near-normal levels. PSPC significantly (p<0.05) reduced the level of reactive oxygen species and inhibited the receptor of advanced glycation end products and thioredoxin interacting protein in the hypothalamus, compared with controls. PSPC preserved the leptin signaling capability, leading to a decrease in hypothalamic adenosine 5'-monophosphate activated protein kinase activity. The anti-obesity effects of PSPC were mediated via attenuation of oxidative stress and regulation of leptin/AMPK signaling in the hypothalamus.

Thermosensitive Gold Nanoparticles Based on Star-Shaped Poly(N-isopropylacrylamide) with a Cubic Silsesquioxane Core

Xiaojing Zhang,Yuelei Hu,Ruixue Liu,Jiashu Sun,Shaoming Fang 한국고분자학회 2015 Macromolecular Research Vol.23 No.3

Collaborative Innovation in Construction Project: A Social Network Perspective

Xiaolong Xue,Ruixue Zhang,Liang Wang,Hongqin Fan,Rebecca J. Yang,Jason Dai 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.2

Successful innovation requires effective cooperation and working relationships among different parties within construction projects. In order to promote construction innovation performance, it is important to shed light on the internal mechanism of innovation through investigating collaborative relationships from a network perspective. In this case, the formation of collaborative relationship can be viewed as a potential generator of innovation processes, and relationship network indicates information exchanges among organizations. This article investigates the collaborative relationship network in a commercial complex by using social network method and in-depth quantitative data analysis. Structural Equation Modeling (SEM) is usually used to analyze the impacts of collaborative relationship on innovation performance in construction projects. There are more and more stakeholders in construction projects, and organization relationship presents a significant network trend. Social network method is widely applied in innovative research. Combined with quantitative data, it is able to quantify and visual the interaction relations of innovation stakeholder. The analytical results will be more objective and reliable. Social network analysis can describe and analyzed collaborative relationship combining qualitative and quantitative method. The results illustrate the relatively dense collaborative relationship networks and highlight the roles that the key members played in the innovation process. The decomposition of collaborative relationship with network analysis contributes to a better understanding of innovation process in construction projects. In particular, key nodes which influence construction innovation through collaborative relationships are revealed and analyzed.

A Novel Procedure for Protection Setting in an HVDC System Based on Fault Quantities

Benfeng Gao,Ruixue Zhang,Xuewei Zhang 대한전기학회 2017 Journal of Electrical Engineering & Technology Vol.12 No.2

HVDC protection setting is difficult to be calculated analytically because of its strong nonlinearity. The currently used setting method is based on the empirical setting of previous projects and then verified by digital simulation. It entails a huge workload and low efficiency. To facilitate protection setting, this paper systematically summarizes the HVDC protection characteristics and then presents a classification of HVDC protections according to the protection principles. On the basis of the fault quantities, a novel setting procedure suitable for travelling wave protection, derivative and level protection, and differential protection is proposed. The proposed procedure is illustrated and verified in detail with the example of travelling wave protection. An HVDC protection setting system that has the functions of automatic protection setting and data management is developed utilizing the C# programming language.

A Novel Procedure for Protection Setting in an HVDC System Based on Fault Quantities

Gao, Benfeng,Zhang, Ruixue,Zhang, Xuewei The Korean Institute of Electrical Engineers 2017 Journal of Electrical Engineering & Technology Vol.12 No.2

HVDC protection setting is difficult to be calculated analytically because of its strong nonlinearity. The currently used setting method is based on the empirical setting of previous projects and then verified by digital simulation. It entails a huge workload and low efficiency. To facilitate protection setting, this paper systematically summarizes the HVDC protection characteristics and then presents a classification of HVDC protections according to the protection principles. On the basis of the fault quantities, a novel setting procedure suitable for travelling wave protection, derivative and level protection, and differential protection is proposed. The proposed procedure is illustrated and verified in detail with the example of travelling wave protection. An HVDC protection setting system that has the functions of automatic protection setting and data management is developed utilizing the C# programming language.