Dual-negative-objective Coordinated Control of Brushless Doubly Fed Induction Generator under Unbalanced Grid Voltage

This article proposes a dual-negative-objective coordinated control strategy for brushless doubly fed induction generator(BDFIG)based wind power generation system under unbalanced grid voltage.To alleviate the mechanical stress and impaction on rotating shaft,the negative control objective(NCO)of machine side converter(MSC)is set to suppress the ripple of electromagnetic torque.While the NCO of grid side converter(GSC)is selected to suppress the oscillation of total output active power or the unbalanced degree of total output current for BDFIG generation system.In comparison with traditional single converter control scheme of the MSC or GSC,dual NCOs can be satisfied at the same time due to the enlarged freedom degree in the proposed improved coordinated control system for back-toback converters.The effectiveness of proposed control strategy is validated by simulation and experimental results on a dual-cagerotor BDFIG(DCR-BDFIG)prototype.

The control and optimization of macro/micro-structure of ion conductive membranes for energy conversion and storage

Ion conductive membranes(ICMs)are frequently used as separators for energy conversion and storage technologies of fuel cells,flow battery,and hydrogen pump,because of their good ion-selective conduction and low electronic conductivity.Firstly,this feature article reviews the recent studies on the development of new nonfluorinated ICMs with low cost and their macro/micro-structure control.In general,these new nonfluorinated ICMs have lower conductivity than commercial perfluorinated ones,due to their poor ion transport channels.Increasing ion exchange capacity(IEC)would create more continuous hydrophilic channels,thus enhancing the conductivity.However,high IEC also expands the overall hydrophilic domains,weakens the interaction between polymer chains,enhances the mobility of polymer chains,and eventually induces larger swelling.The micro-scale expansion and macro-scale swelling of the ICMs with high IEC could be controlled by limiting the mobility of polymer chains.Based on this strategy,some ef ficient techniques have been developed,including covalent crosslinking,semi-interpenatrating polymer network,and blending.Secondly,this review introduces the optimization of macro/microstructure of both perfluorinated and nonfluorinated ICMs to improve the performance.Macro-scale multilayer composite is an ef ficient way to enhance the mechanical strength and the dimensional stability of the ICMs,and could also decrease the content of per fluorosulfonic acid resin in the membrane,thereby reducing the cost of the perfluorinated ICMs.Long side chain,multiple functionalization,small molecule inducing micro-phase separation,electrospun nano fiber,and organic–inorganic hybrid could construct more ef ficient ion transport channels,improving the ion conductivity of ICMs.

Sulfonated polybenzimidazole/amine functionalized titanium dioxide(s PBI/AFT) composite electrolyte membranes for high temperature proton exchange membrane fuel cells usage

The novel sulfonated polybenzimidazole(sPBI)/amine functionalized titanium dioxide(AFT) composite membrane is devised and studied for its capability of the application of high temperature proton exchange membrane fuel cells(HT-PEMFCs),unlike the prior low temperature AFT endeavors.The high temperature compatibility was actualized because of the filling of free volumes in the rigid aromatic matrix of the composite with AFT nanoparticles which inhibited segmental motions of the chains and improved its thermal stability.Besides,amine functionalization of TiO2 enhanced their dispersion character in the sPBI matrix and shortened the interparticle separation gap which finally improved the proton transfer after establishing interconnected pathways and breeding more phosphoric acid(PA) doping.In addition,the appeared assembled clusters of AFT flourished a superior mechanical stability.Thus,the optimized sPBI/AFT(10 wt%) showed 65.3 MPa tensile strength;0.084 S·cm^-1 proton conductivity(at 160℃;in anhydrous conditions),28.6% water uptake and PA doping level of 23 mol per sPBI repeat unit.The maximum power density peak for sPBI/AFT-10 met the figure of0.42 W·cm^-2 at 160℃(in dry conditions) under atmospheric pressure with 1.5 and 2.5 stoichiometric flow rates of H2/air.These results affirmed the probable fitting of sPBI/AFT composite for HT-PEMFC applications.

A new long-side-chain sulfonated poly(2,6-dimethyl-1,4-phenylene oxide)(PPO)/polybenzimidazole(PBI)amphoteric membrane for vanadium redox flow battery

A new amphoteric membrane was prepared by blending long-side-chain sulfonated poly(2,6-dimethyl-1,4-phenylene oxide)(S-L-PPO)and polybenzimidazole(PBI)for vanadium redox flow battery(VRFB)application.An acid-base pair structure formed between the imidazole of PBI and sulfonic acid of S-L-PPO resulted in lowered swelling ratio.It favors to reduce the vanadium permeation.While,the increased sulfonic acid concentration ensured that proton conductivity was still at a high level.As a result,a better balance between the vanadium ion permeation(6.1×10^-9 cm^2·s^-1)and proton conductivity(50.8 m S·cm^-1)in the S-L-PPO/PBI-10%membrane was achieved.The VRFB performance with S-L-PPO/PBI-10%membrane exhibited an EE of 82.7%,which was higher than those of pristine S-L-PPO(81.8%)and Nafion 212(78.0%)at 120 m A·cm^-2.In addition,the S-LPPO/PBI-10%membrane had a much longer self-discharge duration time(142 h)than that of Nafion 212(23 h).

Quaternary-ammonium-immobilized polystyrenes as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate:Effects of linking chains and pendent hydroxyl group

Spherical polystyrene‐supported ammonium salts containing different linking chains between the support and ammonium groups were prepared as efficient and easily reusable heterogeneous catalysts for the cycloadditions of CO2and epoxides.The effects of the length of the linking chains and a hydroxyl group pendent on the linking chain on the catalytic performance of ionic liquid immobilized catalysts and their mechanisms were studied through experiments and density functional theory calculations.It was found that,compared with a short linking chain,a long chain can make the halogen anion more negative and provide a larger contact area of the catalysts with the reactants,thus enhancing the reaction kinetics.The hydroxyl group can stretch the C-O bonds of the epoxides,promoting the reaction thermodynamics.As a result,for the cycloaddition of propylene oxide,the yield of propylene carbonate is much higher for the catalyst with a long linking chain(yield:91.4%)compared with the yield for that with a short chain(yield:70.9%),and is further increased in the presence of pendent hydroxyl groups(yield:98.5%).The catalyst also shows a high catalytic activity even at mild temperature and good reusability(yield:≥96%for10cycles),and the selectivity is always above99%.

Poly(ether ether ketone ketone) based imidazolium as anion exchange membranes for alkaline fuel cells

An imidazolium functionalized poly(ether ether ketone ketone)(PEEKK-DIm OH)anion exchange membrane(AEM)readily soluble in certain low-boiling-point solvents(isopropanol)is prepared.The solubility results are consistent with the results of molecular dynamics simulations.By varying the chloromethylation reaction temperature or concentrated sulfuric acid concentration of PEEKK,the degrees of chloromethylation of PEEKK are changed from 54% to 92%,the corresponding PEEKK-DIm OH AEMs with the ion exchange capacities(IECs)of 1.14–1.65 mmol·g^(-1).The PEEKK-DIm OH 92% AEM shows high hydroxide conductivity(31 m S·cm^(-1)),suitable water uptake(94%)and acceptable swelling ratio(39%)at 60°C.In addition,the PEEKK-DIm OH AEMs possess good thermal and alkaline stability.The maximum power density(46.16 mW·cm^(-2))of fuel cell prepared with PEEKK-DIm OH 92%AEM as exchange membrane and ionomer is much higher than that with commercial AHA membranes.All the above results indicate that the PEEKK used in this study is a promising AEM matrix material for alkaline fuel cells.

喷射混凝土应用及其渗透性、孔结构和力学性能研究

喷射混凝土在我国建设工程中起到越来越重要的作用,本文在国内外研究的基础上,加大了对喷射混凝土性能的研究力度,对喷射混凝土渗透性(透气性、透水性和氯离子迁移)、孔结构(砂浆孔结构和表面孔结构)、力学性能(抗压强度和劈裂抗拉强度)以及作用机理等方面进行探究,研究喷射混凝土配合比对喷射混凝土性能的影响以及三者之间的相互关系,并且介绍了其在施工时需注意的问题及采取的对策措施。

碱性阴离子交换膜的碱稳定性

碱性阴离子交换膜(AEMs)是碱性阴离子交换膜燃料电池的核心部件之一,目前已成为制约碱性阴离子交换膜燃料电池发展的关键因素.离子传导基团在碱性条件下,容易受到氢氧根离子的攻击发生降解.本文主要从以下3个方面介绍了近期AEMs在耐碱稳定性方面的研究成果:(1)开发稳定的离子传导基团,并通过提高离子传导基团的电子密度和增大缺电子位置的空间位阻提高离子基团的稳定性;(2)在离子传导基团与聚合物主链之间引入长烷基侧链;(3)合成不含醚氧键的聚合物主链,改善AEMs的耐碱稳定性.

Prognostic value of high-frequency oscillations combined with multimodal imaging methods for epilepsy surgery

Background:The combination of high-frequency oscillations(HFOs)with single-mode imaging methods has been proved useful in identifying epileptogenic zones,whereas few studies have examined HFOs combined with multimodal imaging methods.The aim of this study was to evaluate the prognostic value of ripples,an HFO subtype with a frequency of 80 to 200 Hz is combined with multimodal imaging methods in predicting epilepsy surgery outcome.Methods:HFOs were analyzed in 21 consecutive medically refractory epilepsy patients who underwent epilepsy surgery.All patients underwent positron emission tomography(PET)and deep electrode implantation for stereo-electroencephalography(SEEG);11 patients underwent magnetoencephalography(MEG).Sensitivity,specificity,positive predictive value,negative predictive value,and accuracy in predicting surgical outcome were calculated for ripples combined with PET,MEG,both PET and MEG,and PET combined with MEG.Kaplan-Meier survival analyses were conducted in each group to estimate prognostic value.Results:The study included 13 men and 8 women.Accuracy for ripples,PET,and MEG alone in predicting surgical outcome was 42.9%,42.9%,and 81.8%,respectively.Accuracy for ripples combined with PET and MEG was the highest.Resection of regions identified by ripples,MEG dipoles,and combined PET findings was significantly associated with better surgical outcome(P<0.05).Conclusions:Intracranial electrodes are essential to detect regions which generate ripples and to remove these areas which indicate good surgical outcome for medically intractable epilepsy.With the assistance of presurgical noninvasive imaging examinations,PET and MEG,for example,the SEEG electrodes would identify epileptogenic regions more effectively.