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Asymmetrical Fault Current Calculation Method and Influencing Factors Analysis of Droop-Controlled Inverters

CSEE Journal of Power and Energy Systems 2024年第2期10卷 562-573页

作者： Huimin zhao zhikang Shuai Jun Ge An Luo Weimin Wu z.John shen College of Electrical and Information Engineering Hunan UniversityChangsha 410006China Electrical Engineering Department Shanghai Maritime UniversityShanghai 201306China Department of Electrical and Computer Engineering Ilinois Institute of TechnologyChicagoIL 60616 USA

Since the fault dynamic of droop-controlled inverter is different from synchronous generators (SGs), protection devices may become invalid, and the fault overcurrent may damage power electronic devices and threaten the safety of the microgrid. Therefore, it is imperative to conduct a comprehensive fault analysis of the inverter to guide the design of protection schemes. However, due to the complexity of droop control strategy, existing literatures have simplified asymmetric fault analysis of droop-controlled inverters to varying degrees. Therefore, accurate fault analysis of a droop-controlled inverter is needed. In this paper, by analyzing the control system, an accurate fault model is established. Based on this, a calculation method for instantaneous asymmetrical fault current is proposed. In addition, the current components and current characteristics are analyzed. It was determined that fault currents are affected by control loops, fault types, fault distance and nonlinear limiters. In particular, the influences of limiters on the fault model, fault current calculation and fault current characteristics were analyzed. Through detailed analysis, it was found that dynamics of the control loop cannot be ignored, the fault type and fault distance determine fault current level, and part of the limiters will totally change the fault current trend. Finally, calculation and experimental results verify the correctness of the proposed method.

关键词： Asymmetrical fault analysis droop control fault current calculation method limiter transient fault characteristics

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PREPARATION OF MESOPOROUS CARBON BY CARBON DIOXIDE ACTIVATION WITH CATALYST

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Acta Metallurgica Sinica(English Letters) 2002年第1期15卷 67-72页

作者： W.z. shen A.H. Lu J.T. zheng Institute of Coal Chemistry The Chinese Academy of Sciences Taiyuan 030001 China

A mesoporous activated carbon (AC) can be successfully prepared by catalytic activation with carbon dioxide. For iron oxide as catalyst, there were two regions of mesopore size distribution, i.e. 2-5nm and 30-70nm. When copper oxide or magnesium oxide coexisted with iron oxide as composite catalyst, the content of pores with sizes of 2-5nm was decreased, while the pores with 30-70nm were increased significantly. For comparison, AC reactivated by carbon dioxide directly was also investigated. It was shown that the size of mesopores of the resulting AC concentrated in 2-5nm with less volume. The adsorption of Congo red was tested to evaluate the property of the result-ing AC. Furthermore, the factors affecting pore size distribution and the possibility of mesopore formation were discussed.

关键词： activated carbon mesopore. catalytic activation

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SiC JFETs Modular Cascaded Method with Active Clamp Control Strategy for DC Solid-state Circuit Breaker

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CSEE Journal of Power and Energy Systems 2023年第6期9卷 2435-2446页

作者： Hong Duan Wei Wang zhikang Shuai Dong He Daixin Chen z.John shen the College of Electrical and Information Engineering Hunan UniversityChangsha 410006China the Department of Electrical and Computer Engineering Illinois Institute of TechnologyChicagoIL 60616 USA.

Power semiconductor devices cascaded topology is one of the most common solutions for solid-state circuit breakers(SSCBs)working in medium-voltage DC ***,when the number of cascaded devices is large,current series technologies of power semiconductor devices will be difficult to be applied since with uneven voltage sharing ***,this paper proposes a novel cascade method of multi-SiC JFETs based on modules *** method consists of two parts:one is a single-gate driver cascaded SiC JFETs topology which is used to form the module,the other one is an active clamp control strategy which ensures that each module is protected from overvoltage when modules are *** proposed cascade method can effectively suppress voltage overshoot of cascading power devices in the switching *** on the proposed cascade method,a 5kV/63A SSCB prototype is ***,an experiment is conducted based on the designed *** results validate the effectiveness of the proposed cascaded method for SSCB.

关键词： Active control clamp DC solid-state circuit breaker modular SiC JFETs series connection

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Experimental study of compressible boundary layer on a cone at angles of attack

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Acta Mechanica Sinica 2009年第3期25卷 325-333页

作者： A.Maslov D.Bountin A.Shiplyuk A.Sidorenko Q.shen z.Bi Khristianovich Institute of Theoretical and Applied Mechanics(ITAM)and Novosibirsk State University China Academy of Aerospace Aerodynamics(CAAA)

Experimental study was conducted for boundarylayers on a sharp 5° half-angle cone of 400mm length at angles of attack. The model was tested in the T-326 hypersonic wind tunnel （ITAM） at freestream Mach number M = 5.95. Mean and fluctuation wall characteristics of the boundary layer are measured at 0°, 2°, 3° and 4° angles of attack for different stagnation pressures. Pulsation measurements are carried out by means of ALTP sensor. Pressure and temperature distributions along the model are obtained, and transition beginning and end locations have been found. Boundary layer stabilization with the increase of angle of attack and the decrease of stagnation pressure is observed. High frequency pulsations inherent to hypersonic boundary layer （second mode） have been detected.

关键词： Compressible boundary layer Transition,Experimental study

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Grain refinement mechanism of Mg-3Sn-1Mn-1La alloy during accumulative hot rolling

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Journal of Materials Science & Technology 2021年第32期91卷 251-261页

作者： z.Y.zhao R.G.Guan Y.F.shen P.K.Bai School of Materials Science and Engineering North University of ChinaTaiyuan 030051China bEngineering Research Center of Continuous Extrusion Ministry of EducationDalian Jiaotong UniversityDalian 116028China Key Laboratory for Anisotropy and Texture of Materials Northeastern UniversityShenyang 110004China

We elucidate the effect of lanthanum(La) on the grain refinement of Mg-3 Sn-1 Mn alloy during accumulative hot rolling. The lath-shaped Mg_(2) Sn phase in the Mg-3 Sn-1 Mn alloy is firstly broken and spheroidized,and then the size increases and coarsens with the increase of rolling reduction, most of Mg_(2) Sn move from grain boundary to grain and are homogeneously distributed within the matrix. However, the plate-shaped Mg Sn La compound in Mg-3 Sn-1 Mn-1 La gradually becomes fine, spheroidized, and homogeneously distributed. The grain sizes of Mg-3 Sn-1 Mn and Mg-3 Sn-1 Mn-1 La alloys become fine through dynamic recrystallization(DRX), though the grain refinement of Mg-3 Sn-1 Mn-1 La alloy is better compared to the Mg-3 Sn-1 Mn alloy. A large number of uniformly distributed spherical Mg Sn La compounds pin the dislocations, thus increasing the dislocation density. Hence, the driving force for DRX increases and promotes the formation of deformation bands and more twins, providing the sites for DRX nucleation and growth.

关键词： Mg alloy Grain refinement Dynamic recrystallization Accumulative hot rolling

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Effects of Mixing Volume and Initial Particle Size Distribution of Fly Ash on Pore Solution of Cement Paste

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武汉理工大学学报 2010年第17期32卷 112-116页

作者： SHUI z H DUAN P shen C H School of Materials Science and Engineering Wuhan University of TechnologyWuhan 430070China Center of Materials Research and Analysis Wuhan University of TechnologyWuhan 430070China

The effects of fly ash with different mixing volume and different particle sizes on pore solution of cement-based materials were studied. The pore solution was extracted by squeezing at scheduled ages. The particle size distribution of fly ash was classified as smaller than 45 μm and 45～80 μm,and the mixing volume was classified as 10% and 20%. The concentrations of K+,Na+ and Ca2+ were measured using Inductively Coupled Plasma Emission Spectrometer (ICP),and the pH was measured by acid-base titration. The results indicate that the concentrations of various ions were prompted at the initial time of the hydration. With further hydration,ion concentrations of K+ and Na+ raise again and finally stabilized,but there is a certain decline on Ca2+ later on. It also shows that fly ash exhibited great effect on the hydration of cement,it can lower the concentration of Ca2+ and pH of the pore solution,but raise the concentrations of K+ and Na+. More importantly,ion concentrations of K+,Na+ and Ca2+ reduced with smaller particle sizes of fly ash.

关键词： cement-based materials pore solution ion concentration squeeze

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Mechanical properties of Al/a-C nanocomposite thin films synthesized using a plasma focus device

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Chinese Physics B 2014年第2期23卷 353-358页

作者： z.A.Umar R.S.Rawat R.Ahmad A.K.Kumar Y.Wang T.Hussain z.Chen L.shen z.zhang NSSE National Institute of EducationNanyang Technological University Department of Physics GC University Center for Advanced Studies in Physics (CASP) GC University School of Materials Science and Engineering Nanyang Technological University Institute of Materials Research and Engineering ASTAR (Agency for ScienceTechnology and Research)3 Research Link

The Al/a-C nanocomposite thin films are synthesized on Si substrates using a dense plasma focus device with alu- minum fitted anode and operating with CH4/Ar admixture. X-ray diffractometer results confirm the formation of metallic crystalline Al phases using different numbers of focus shots. Raman analyses show the formation of D and G peaks for all thin film samples, confirming the presence of a-C in the nanocomposite thin films. The formation of Al/a-C nanocomposite thin films is further confirmed using X-ray photoelectron spectroscopy analysis. The scanning electron microscope results show that the deposited thin films consist of nanoparticles and their agglomerates. The sizes of th agglomerates increase with increasing numbers of focus deposition shots. The nanoindentation results show the variations in hardness and elastic modulus values of nanocomposite thin film with increasing the number of focus shots. Maximum values of hardness and elastic modulus of the composite thin film prepared using 20 focus shots are found to be about 10.7 GPa and 189.2 GPa, respectively.

关键词： dense plasma focus X-ray photoelectron spectroscopy field emission scanning electron micro- scope elastic modulus

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Interfacial bonding mechanism in Al/coated steel dissimilar refill friction stir spot welds

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Journal of Materials Science & Technology 2019年第6期35卷 1027-1038页

作者： z. shen Y. Ding J. Chen B. Shalch Amirkhiz J.z. Wen L. Fu A.P. Gerlich School of Materials Science and Engineering Northwestern Poly technical University Xi'an 710072 China Shanxi Key Laboratory of Friction Welding Technologies Northwestern Polytechnical University Xi'an 710072 China State Key Laboratory of Solidification Processing Northwestern Poly technical University Xi'an 710072 China Centre of Advance Materials Joining Department of Mechanical and Mechatronics Engineering University of Waterloo 200 University Ave. Waterloo N2L3G1 Ontario Canada CanmetMATERIALS Natural Resources Canada Hamilton L8P 0A5 Canada

Defect-free dissimilar Al/zinc coated steel and Al/AlSi coated steel welds were successfully fabricated by refill friction stir spot welding. However, Al alloy and uncoated steel could not be welded under the same welding condition. Al-zn eutectic layer formed at the Al/zinc coated steel interface showed nonuniformity in thickness and nanoscale intermetallic(IMC) produced was discontinuous. The bonding formation between the Al-zn layer and the surrounding materials was attributed to a liquid/solid reaction mechanism. Bonding formation at Al alloy and AlSi coated steel interface was attributed to a solid/solid reaction mechanism, as the joining process did not involve with melting of base metals or AlSi coating materials. Kissing bond formed at the weld boundary acted as a crack initiation and propagation site,and the present study showed that weld strength of Al 5754/AlSi coated steel was greatly influenced by properties of original IMC layer.

关键词： Refill friction stir spot welding Al alloy Steel Coated materials Joining mechanism

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STUDY ON TEMPERATURE FIELD INDUCED IN HIGH FREQUENCY INDUCTION HEATING

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Acta Metallurgica Sinica(English Letters) 2006年第3期19卷 190-196页

作者： H. shen z.Q. Yao Y.J. Shi J. Hu School of Mechanical Engineering Shanghai Jiaotong University Shanghai 200030 China

A mathematical model was established for the temperature field developed during high frequency induction heating （HFIH） by Maxwell＇s equations. It required solving the coupled equations of the electromagnetic and temperature fields. The numerical simudation was performed using FEMLAB. The comparison of the calculations using the proposed model with experimental results showed a very good correlation. The effects of the heating parameters in high frequency induction such as the distance between the plate and the coil, the applied current, the frequency, and the turns of the coil on the temperature profiles developed in the plate were also discussed using the established model.

关键词： high frequency induction temperature field numerical simudation

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NUMERICAL INVESTIGATION OF STRAIGHT-LINE LASER FORMING UNDER THE TEMPERATURE GRADIENT MECHANISM

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Acta Metallurgica Sinica(English Letters) 2006年第2期19卷 144-150页

作者： Y.J. Shi H. shen z.Q. Yao J. Hu School of Mechanical and Power Engineering Shanghai Jiaotong University Shanghai 200030 China

Laser forraing is a new flexible and dieless forming technique. To achieve the high accuracy forming, the temperature gradient mechanism （TGM） is studied. In the analysis of TGM, the plate bends about x-axis and about y-axis as well. To understand the deformation trend, the numerical simulation of deformation of plate is conducted by choosing different laser powers, laser spot diameters, scanning speeds, lengths, widths and thicknesses. From the results of simulation, it can be seen that the laser spot diameter, the scanning speed, laser power and thickness of plate play dominant roles in the laser forming process. However, the bending angles αx and αy show different trends with the variation of parameters. In addition, in comparison with above four parameters, the effect of length and width of plate on the beading angle may be neglected, but their effects are significant for the bending radius R.

关键词： laser forming temperature gradient mechanism metal plate

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