Improved synergetic excitation control for transient stability enhancement and voltage regulation of power systems

This paper proposes decentralized improved synergetic excitation controllers (ISEC) for synchronous generators to enhance transient stability and obtain satisfactory voltage regulation performance of power systems. Each generator is considered as a subsystem, for which an ISEC is designed. According to the control objectives, a manifold, which is a linear combination of the deviation of generator terminal voltage, rotor speed and active power, is chosen for the design of ISEC. Compared with the conventional synergetic excitation controller (CSEC), a parameter adaptation scheme is proposed for updating the controller parameter online in order to improve the transient stability and voltage regulation performance simultaneously under various operating conditions. Case studies are undertaken on a single-machine infinite-bus power system and a two-area four-machine power system, respectively. Simulation results show the ISEC can provide better damping and voltage regulation performance, compared with the CSEC without parameter adaptation scheme and the conventional power system stabilizer.     

A facile hydrothermal synthesis of visible-light responsive BiFeWO6/MoS2 composite as superior photocatalyst for degradation of organic pollutants

In the present study, we have fabricated a new Z-scheme BiFeWO₆/MoS₂ composite for photocatalytic elimination of organic contaminants from the waste-water. A series of BiFeWO₆/MoS₂ composites were obtained by changing the amounts of BiFeWO₆ from 1 to 10 mg through a facile hydrothermal method. The phase structures and morphologies of these BiFeWO₆/MoS₂ composites were analyzed by SEM, HR-TEM, XRD, UV–vis DRS, element mapping and XPS techniques. Afterward, the dye-degradation experiments were conducted for the removal of Rhodamine B (RhB) using as-obtained BiFeWO₆/MoS₂ composite samples under visible-light illumination to evaluate their photocatalytic activity. It is found that the BiFeWO₆/MoS₂ composites exhibited great photocatalytic behavior than the pure BiFeWO₆ and MoS₂ samples. In particular, the BiFeWO₆/MoS₂ composite with 5 mg of BiFeWO₆ showed a quickly complete photocatalyst degradation ability of RhB in 75 min with high photo-stability and reusability behavior. This superior catalytic response of BiFeWO₆/MoS₂ composite may be contributed by its high light harvesting capacity as well as fast separation and movement of photo-generated electron-hole pairs. This proposed BiFeWO₆/MoS₂ composite is a very promising photocatalyst for environmental remediation work.     

Ruthenium stabilized on transition metal-on-transition metal oxide nanoparticles for naphthalene hydrogenation

The multi-metallic nanocatalysts of ruthenium nanoclusters-on-transition metal/transition metal oxide nanoparticles (TM/TMO NPs) then supported on carbon (Ru/Ni/NiO/C or Ru/Co/Co₃O₄/C) were designed and synthesized. The Ni/NiO or Co/Co₃O₄ NPs strongly stabalized the ruthenium nanoclusters by the interfacial interaction among them. These catalysts exhibited high catalytic activity and 100% selectivity to decalin for naphthalene hydrogenation due to the synergy effect of multiple catalytic sites, where naphthalene was absorbed and activated at the TMO sites (NiO or Co₃O₄), H₂ was activated at the Ru sites and it produced the activated H* species, H* was transferred to the surface of NiO or Co₃O₄ by the hydrogen spillover effect of TM (Ni or Co), reacting with the activated naphthalene and forming decalin. The nanostructures and synergetic effect of the Ru/Ni/NiO/C and Ru/Co/Co₃O₄/C catalysts were revealed by a series of techniques, such as high-resolution transmission electron microscope (HRTEM), temperature-programmed reduction (TPR), scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDS) mapping, high-sensitivity low-energy ion scattering (HS-LEIS) and X-ray absorption spectroscopy (XAS). It is promising that the hydrogen storage can proceed at room temperature via catalyzing naphthalene hydrogenation over the Ru/Ni/NiO/C or Ru/Co/Co₃O₄/C catalyst.     

Facile synthesis of the encapsulation of Co-based multimetallic alloys/oxide nanoparticles nirtogen-doped carbon nanotubes as electrocatalysts for the HER/OER

The pivotal challenge of electrocatalysis remains the development of highly effective electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, a universal strategy of preparing the encapsulation of Co-based multimetallic alloys/oxide nanoparticles in nitrogen-doped carbon nanotubes (named CoM@CNTs, M = Ni/Mn/Fe) was induced by annealing mixtures of the as-synthesized precursor, ethanol and different metallic acetates, including binary CoNi@CNTs, ternary CoNi/MnO@CNTs and quaternary CoNiFe/MnO@CNTs. By virtue of its unique structure with a high electrical conductive network based on CNT substrates, abundant catalytic active sites supplied by multimetallic nanoparticles and protection against nanoparticle corrosion by N-doped carbon layers, the as-synthesized CoNiFe/MnO@CNTs electrocatalyst has remarkable HER properties with a low overpotential of 122 mV and OER activity with a low overpotential of 275 mV at 10 mA cm^?2 and excellent stability and durability under long-term testing in alkaline solutions. Therefore, this strategy will provide a new route for fabricating multimetallic-based CNTs as HER/OER electrocatalysts with excellent stability and high catalytic activity.     

碱集料反应与冻融循环协同作用对混凝土破坏的影响

研究了碱集料反应与冻融循环协同作用下的混凝土的破坏行为，结果表明，当混凝土先进行碱集料反应试验而随后再冻融时，碱集料反应对冻融循环有促进作用，随着碱集料反应程度的提高，混凝土开裂愈严重，随后表现的混凝土抗冻性愈差；然而当混凝土先冻融，而后再进行碱集料反应时，冻融循环对碱集料反应的促进作用则不大，随着冻融次数的增加，混凝土破坏程度增大，在继续进行的碱集料反应结束时，混凝土最终膨胀值增大，相对动弹模量损失增大，但是混凝土劣化速度则相差不大。     

Promoted hydrolysis performances and mechanism of Si-NaBH4-AlCl3 in deionized water

Si-based hydrolysis material system can be used in mobile/portable hydrogen source applications connected to fuel cells but is limited by alkaline solutions. In the present research, we reported an acid/alkaline free hydrolysis system combining silicon with NaBH₄. Samples with different ratios between Si and NaBH₄ are prepared via high energy ball milling and hydrolyzed in deionized water at different temperatures. Synergetic effect between silicon and NaBH₄ was found in the hydrolysis process. 2Si-NaBH₄ sample displays the best hydrolysis performances with the hydrogen yield of 1594 ml⋅g⁻¹ in deionized water at 70 °C. Thereafter, AlCl₃ is added into the 2Si-NaBH₄ sample to further improve its comprehensive properties. The effect of AlCl₃ content and promotion mechanism of the reaction are explored. 2Si-NaBH₄–5 wt% AlCl₃ sample shows a significant improvement with a high hydrogen yield of 1689 ml·g⁻¹ in deionized water at 70 °C and a corresponding conversion rate of 95.8%, indicating that the Si-NaBH₄-AlCl₃ composite is promising to be a hydrogen source in applications of mobile/portable fuel-cell-powered facilities.     

A facile one-pot synthesis of microspherical-shaped CoS2/CNT composite as Pt-free electrocatalyst for efficient hydrogen evolution reaction

Hydrogen evolution reaction has been recognized as a green technology in the field of electrochemical energy conversion and storage devices. Nevertheless, it is necessary task to finding an economical and effective electrocatalysts for HER. Among the different HER catalysts, the cobalt disulfide (CoS₂) showed an excellent HER activity owing to its low cost, easy to synthesize and good stability. Hence, in this work, we prepared a series of CoS₂/CNT composites with different contents CNT from 4 to 12 wt% by a simple one-step hydrothermal method to investigate the influence of CNT on HER activity of CoS₂. The structural and morphological properties of the obtained samples were analyzed through XRD, SEM, HR-TEM, and XPS. The SEM images of CoS₂/CNT composite showed the spherical-shaped CoS₂ covered by the CNT nanostructure. In addition, the electrochemical tests were carried out using 0.5 M H₂SO₄ solution in order to assess their HER activity. The attained electrochemical results showed that the CoS₂/CNT composite with 8% CNT offers an outstanding HER activity with the smallest overpotential of 155 mV at 10 mA cm⁻² and lowest Tafel slope of 59 mV dec⁻¹ when compared with other composites. Also, the optimized CoS₂/CNT composite provided excellent stability in the acidic medium after 1000 cycles. Therefore, the as-synthesized CoS₂/CNT composite will be an efficient, low-cost and Pt-free electrocatalyst for HER application.     

Reaching phase free adaptive fuzzy synergetic power system stabilizer

In this paper, an adaptive fuzzy power system stabilizer is developed based on robust synergetic control theory and terminal attractor techniques. The main contribution consists in making the dynamic system insensitive to parameters variation. This aim is achieved using a new synergetic controller design such that power system states start, evolve and remain on a designer chosen attractor toward the equilibrium point therefore avoiding transient mode. Rendering the design more robust, fuzzy logic systems are used to approximate the unknown power system dynamic functions without calling upon usual model linearization and simplifications. Based on an indirect adaptive scheme and Lyapunov theory, adaptation laws are developed to make the controller handle parameters variations due to the different operating conditions occurring on the power system and to guarantee stability. The performance of the proposed stabilizer is evaluated for a single machine infinite bus system and for a multi machine power system under different type of disturbances. Simulation results show the effectiveness and robustness of the proposed stabilizer in damping power system oscillations under various disturbances and better overall performance than classical PSS and some other types of power stabilizers.     

Synergetic effects of temperature and magnetic field on the aragonite and calcite growth

The effects of temperature and magnetic field on aragonite and calcite growth were investigated in a stirred-tank crystallizer, using the constant-composition technique. At room temperature without magnetization, the calcite seeds grew but the aragonite did not. When the growth rates of the aragonite and calcite seeds were measured in the presence of a magnetic field at temperatures above room temperature, the synergetic effects were significant but with differing effects on the different seeds. The cluster-transformation mechanism was used to explain the growth rate data. Finally, the aragonite growth rate data were compared with data obtained in a fluidized bed.