Coordinated Damping Control Design for Power System With Multiple Virtual Synchronous Generators Based on Prony Method

With more renewables integrated into power grids, the systems are being transformed into low inertia power electronic dominated systems. In this situation, the virtual synchronous generator (VSG) control strategy was proposed to deal with insufficient inertia challenge caused by the reduction of synchronous generation. However, as the VSG control method emulates the dynamic behavior of traditional synchronous machines, the interaction between multiple VSG controllers and synchronous generators (SGs) may cause low-frequency oscillation similar to that caused by the interaction between multiple SGs. This paper reveals that the system low-frequency oscillatory modes are affected by multiple VSGs. Then Prony analysis is utilized to extract the system mode information which will be subsequently used for VSG controller design, and a decentralized sequential coordinated method is proposed to design the supplementary damping controller (SDC) for multiple VSGs. The system low-frequency oscillation is first analyzed based on a modified two-area system with a linearized state-space model, and a further case study based on a revised New England 10-machine 39-bus system is used to demonstrate the effectiveness of the proposed coordinated method for multiple VSGs

Study on elastohydrodynamic lubrication performance of double-layer composite water-lubricated bearings

Double-layer composite water-lubricated bearing is a new type of water-lubricated bearing which can integrate the good damping performance of low elastic under-layer bush and good tribological performance of plastic layer bush. This paper analyzes its elastohydrodynamic lubrication performance by fluid–structure interaction (FSI) method, and studies the effects of eccentricity ratio, rotational speed, elastic modulus distribution and thickness distribution of bearing bush on its lubrication performance. Results show that the lubrication performance of double-layer bearing is more like that of plastic bearing. As rotational speed and eccentricity ratio increase, the maximum water film pressure, the load carrying capacity and the maximum bush deformation increase significantly. As the elastic modulus of the low elastic under-layer bush decreases, the total bush deformation increases significantly, but the load carrying capacity decreases slightly. The bush thickness distribution influences the deformation distribution of both low elastic under-layer bush and plastic layer bush, but have little impact on the total bush deformation and bearing lubrication performance

Control of Streptomyces alfalfae XY25T Over Clubroot Disease and Its Effect on Rhizosphere Microbial Community in Chinese Cabbage Field Trials

Clubroot caused by Plasmodiophora brassicae is one of the most destructive diseases in cruciferous crops. Streptomyces alfalfae XY25T, a biological control agent, exhibited great ability to relieve clubroot disease, regulate rhizosphere bacterial and fungal communities in Chinese cabbage, and promote its growth in greenhouse. Therefore, field experiments were carried out to investigate the effects of S. alfalfae XY25T on clubroot and rhizosphere microbial community in Chinese cabbage. Results showed that the control efficiency of clubroot by S. alfalfae XY25T was 69.4%. Applying the agent can alleviate soil acidification; increase the contents of soil organic matter, available nitrogen, available phosphorus, and available potassium; and enhance activities of invertase, urease, catalase, and alkaline phosphatase. During Chinese cabbage growth, bacterial diversity decreased first and then increased, and fungal diversity decreased gradually after inoculation with S. alfalfae XY25T. High-throughput sequencing analysis showed that the main bacterial phyla were Proteobacteria, Bacteroidetes, Acidobacteria, and Planctomycetes, and the major fungal phyla were Ascomycota and Basidiomycota in rhizosphere soil. The dominant bacterial genera were Flavobacterium, Candidatus, Pseudomonas, Stenotrophomonas, Sphingomonas, Flavisolibacter, and Gemmatimonbacteria with no significant difference in abundance, and the major fungal genera were Monographella, Aspergillus, Hypocreales, Chytridiaceae, Fusarium, Pleosporales, Agaricales, Mortierella, and Pleosporales. The significant differences were observed among Pleosporales, Basidiomycota, Colletotrichum, two strains attributed to Agaricales, and another two unidentified fungi by using S. alfalfae XY25T. Moreover, quantitative real-time PCR results indicated that P. brassicae content was significantly decreased after the agent inoculation. In conclusion, S. alfalfae XY25T can affect rhizosphere microbial communities; therefore, applying the agent is an effective approach to reduce the damage caused by clubroot

Raw rehmannia radix polysaccharide can effectively release peroxidative injury induced by duck hepatitis A virus

Background: Duck viral hepatitis (DVH), caused by duck hepatitis A virus (DHAV), is a fatal contagious infectious disease which spreads rapidly with high morbidity and high mortality, and there is no effective clinical drug against DVH.Materials and Methods: Raw Rehmannia Radix Polysaccharide (RRRP), Lycii Fructus polysaccharides and Astragalus Radix polysaccharides were experimented in vitro and in vivo. Mortality rate, livers change, liver lesion scoring, peroxidative injury evaluation indexes in vitro and in vivo, and hepatic injury evaluation indexes of optimal one were detected and observed in this experiment.Results: RRRP could reduce mortality with the protection rate about 20.0% compared with that of the viral control (VC) group, finding that RRRP was the most effective against DHAV. The average liver scoring of the VC, blank control (BC), RRRP groups were 3.5, 0, 2.1. Significant difference (P<0.05) appeared between any two groups, demonstrating that it can alleviate liver pathological change. RRRP could make the hepatic injury evaluation indexes similar to BC group while the levels of the VC group were higher than other two groups in general. The levels of SOD, GSH-Px, CAT of RRRP group showed significant higher than that of VC group while the levels of NOS and MDA showed the opposite tendency, thus, RRRP could release peroxidative injury.Conclusion: RRRP was the most effective against duck hepatitis A virus (DHAV). RRRP could reduce mortality, alleviate liver pathological change, down-regulate liver lesion score, release peroxidative injury and hepatic injury. The antiviral and peroxidative injury releasing activity of RRRP for DHAV provided a platform to test novel drug strategies for hepatitis A virus in human beings.Keywords: Raw Rehmannia Radix Polysaccharide; duck hepatitis A virus; peroxidative injury; hepatic injur