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Decentralized control strategy for storage systems in islanded microgrids
Liwei Zhang,Lei Dai,Changming Zhao 전력전자학회 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.12
This paper presents a decentralized control strategy for the distributed storage (DS) systems of the islanded microgrid composed of distributed generations (DGs) and DSs. Each of the DSs consists of a bidirectional DC-DC converter cascaded with a three-phase inverter. Control strategies for DSs and DGs are based on droop control. The line frequency of the point of common coupling (PCC) is an agent to regulate the active power of the DS. Due to the power mismatch among the supplies and load demands of DGs, the frequency controller of the DS generates its active power reference. In addition, the frequency deviation caused by droop control can be reduced. Reactive load power is almost equally shared by all of the constituent units. Therefore, the DS works by charging or discharging the energy storage devices. Simulation and experimental results are provided to verify the effectiveness of the proposed control strategy.
Improving performance of medical image alignment through super-resolution
Liwei Deng,Yuanzhi Zhang,Jing Wang,Sijuan Huang,Xin Yang 대한의용생체공학회 2023 Biomedical Engineering Letters (BMEL) Vol.13 No.3
Medical image alignment is an important tool for tracking patient conditions, but the quality of alignment is influenced bythe effectiveness of low-dose Cone-beam CT (CBCT) imaging and patient characteristics. To address these two issues, wepropose an unsupervised alignment method that incorporates a preprocessing super-resolution process. We constructed themodel based on a private clinical dataset and validated the enhancement of the super-resolution on alignment using clinicaland public data. Through all three experiments, we demonstrate that higher resolution data yields better results in the alignmentprocess. To fully constrain similarity and structure, a new loss function is proposed; Pearson correlation coefficientcombined with regional mutual information. In all test samples, the newly proposed loss function obtains higher resultsthan the common loss function and improve alignment accuracy. Subsequent experiments verified that, combined with thenewly proposed loss function, the super-resolution processed data boosts alignment, can reaching up to 9.58%. Moreover,this boost is not limited to a single model, but is effective in different alignment models. These experiments demonstratethat the unsupervised alignment method with super-resolution preprocessing proposed in this study effectively improvedalignment and plays an important role in tracking different patient conditions over time.
Jing Zhang,Fengjing Bu,Yongqiang Dai,Liwei Xue,Zhixian Xu,Seung-Kon Ryu,Riguang Jin 한국탄소학회 2010 Carbon Letters Vol.11 No.1
The precipitation polymerization of acrylonitrile (AN) was carried out in a mixture solution of dimethyl sulfoxide (DMSO) and water at 50~65℃ using α,α'-azobisisobutyronitrile (AIBN) as an initiator. The increased molecular weight polyacrylonitrile (PAN) was prepared with increasing the H2O/DMSO ratio from 10/90 to 80/20. The viscosity average molecular weight of H2O/DMSO solvent was 4.4 times larger than that of H2O/DMF solvent, and precipitation polymerization was accelerlated due to the far decreased chain transfer effect of DMSO. Based on the experimental results, the increased PAN molecular weight was regarded as the summation of two mechanisms: i) particle-particle aggregation and ii) particle-radical attachment. The theoretical equation derived from the mechanisms was well coincided with the experimental results showing the linear relationship between the viscosity average molecular weight and the H2O/DMSO ratio.
Miaomiao Zhang,Wei Hong,Fangxi Xie,Yan Su,Liwei Han,Bin Wu 한국자동차공학회 2018 International journal of automotive technology Vol.19 No.3
A detailed investigation of the impact of injection timing and injection pressure on combustion and particles of a spray-guided GDI engine was conducted, under different engine operating conditions. The results indicated that, more proportion of large particles were emitted when increasing engine load, and the peak of accumulation mode particles moved toward smaller size when rising engine speed. With retarding the injection timing, the in-cylinder pressure and heat release rate rose first and then dropped at 2000 rpm, but they continuously rose at lower or higher speed conditions. The total particles concentration curves at all cases showed a trend of U-shape, and the corresponding timing of the lowest particles concentration advanced as the engine speed or load increased. The minimum value of emitted particles first rose and then fell when increasing load at 2000 rpm conditions, and it continuously rose when increasing speed at 40 Nm conditions. Generally, injection pressure did no sensitively affect combustion process except that it showed a relatively strong impact at low load conditions. However, particulate matter could be effectively inhibited by elevating fuel pressure from 5.5 to 11.5 MPa at all cases. In detail, the total particles concentration continuously fell at low speed and mid speed-high load cases, but it showed a rose trend when further increase fuel injection pressure at mid speed-low load and high-speed conditions.
You Zhou,Liwei Xue,Kai Yi,Li Zhang,Seung Kon Ryu,Ri Guang Jin 한국탄소학회 2012 Carbon Letters Vol.13 No.3
A new model and resultant equation for the coagulation of acrylonitrile monomers in precipitation polymerization are suggested in consideration of the surface tension (γ) and cohesive energy density (ECED). The equation was proven to be quite favorable by considering figure fittings from known surface tensions and cohesive energy densities of certain organic solvents. The relationship between scale value of surface tension (γ/M) and cohesive energy density of monomers can be obtained by changing the coagulation bath component for effective precipitation polymerization of acrylonitrile in wet spinning.
Wusong Wang,Liwei Zhang,Liqing Shang,Yewen Zhang 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.9
In connection with an analogue of electromagnetically-induced transparency (EIT), this paper studied experimentally the tunable band-pass filter and tunable slow-wave effect of MDM (μ-negative materials/double positive materials/μ-negative materials) magnetic plasmonic channel. The results of simulations and experiments show that an evident electromagnetically-induced transparency phenomenon appears in this channel with double-side resonators, which can be used to realize simultaneous the band-pass filter and the slow-wave effect. The band-pass filter’s center frequency is founded to be determined by the size of the side resonator, the resonator direction and the effective permeability of μ-negative (MNG) metamaterials. The bandwidth can be adjusted by detuning of the two resonator frequencies, the band size of the band-pass filter depends on the number of the resonators, Thus, the band-pass filter characteristics of the MDM waveguide can be tuned by changing the resonator parameters, the resonator direction and the effective permeability of the MNG materials. Moreover, the MDM structure can also be utilized to obtain a tunable slow-wave effect (such as an adjustable frequency, a slow-down factor, and even a muti-band slow wave) based on EIT. The experimental results are in good agreement with the simulation results.
Yutian Fan,Liwei Lu,Tao Zhou,Hua Zhang,Fugang Qi,Min Ma,Zhiqiang Wu,Weitao Jia,Sha Zhang,Weiying Huang 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.10
In this work, a novel process of repeated upsetting-extrusion (RUE) was used to fabricate the AQ80 magnesium (Mg) alloy. The effects of deformation passes on the microstructure and microhardness of the RUEed AQ80 Mg alloy were studied. The results showed that {10–12} extension twins appeared in the sample after 1 pass of deformation compared to the initial sample, which divided the coarse grains and achieved the preliminary refinement of the grains. The grains were uniformly refined further with increasing RUE deformation passes, and after 3 passes, the average grain size was reduced from 27.4 to 3.0 μm. The grains were refined mainly by continuous dynamic recrystallization (CDRX), particle-stimulated nucleation (PSN), and discontinuous dynamic recrystallization (DDRX) mechanisms. After RUE deformation, the peak component of the texture was tilted by 0–20° toward the extrusion direction (ED) because of the increased activation of pyramidal < c + a > slip. The microhardness of the 3-pass RUE deformed sample increased by 12.9% compared to the initial sample. This is mainly attributable to fine-grained strengthening and second phase strengthening.
Pengyu Li,Liwei Mi,Yuanyuan Liu,Wenqin Zhang,Xian-Lei Shi 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-
A series of monofunctional and bifunctional polyacrylonitrilefiber catalysts have been successfullyprepared to catalyze the decarboxylative Doebner–Knoevenagel reaction of aldehydes and monoethylmalonate for the syntheses of the (E)-α,β-unsaturated esters. Among which, the catalyst PANPDFII/I showsthe best synergistic catalytic activity with high yields (89–96%), stereoselectivities (Z:E > 99:1) andreusability (up to 8 times). The influences of the N position on aminopyridine moiety, solvent andtemperature on the catalytic system were investigated in detail. This catalytic system can process well inhigher or lower polar organic solvents instead of moderate polar solvents, which is an interestingphenomenon in organic catalysis, and the reasons are explained in this work. Furthermore, a DMAP (4-dimethylaminopyridine) and piperazine synergistic catalytic mechanism in the micro-environment ofthefiber catalyst has been conceived to explain the high catalytic performance of this catalytic system. Besides, thefiber catalyst PANPDFII/I shows high application potential in industry for its good performancein scaled-up experiment, as well as its advantages of the easy preparation, high mechanical strength,flexibility and high stability in air.