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Characterization,Removal and Evaluation of Oxide Film in the Diffusion Bonding of Zr_(55)Cu_(30)Ni_5Al_(10) Bulk Metallic Glass

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Journal of Materials Science & technology 2014年第7期30卷 722-730页

作者： Haiyan Chen Jian Cao Xiaoguo Song Jiakun Liu Jicai Feng State Key Lab of Advanced Welding and Joining Harbin Institute of Technology School of Materials Science and Engineering Harbin Institute of Technology at Weihai

The composition of oxide film of ZrssCu3oNi5Al10 bulk metallic glass was identified by X-ray photoelectron spectroscopy. In addition, the relatively sound joints of bulk metallic glass without macroscopic deformation were obtained by removing the oxide film before diffusion bonding. The joint interfaces were observed by scanning electron microscopy and atomic force microscopy. The hardness of joints near the interface was higher than that far away from the interface, which is attributed to the difference of structural relaxation. According to the result of micro-focused X-ray diffractometry and transmission electron microscopy, the joints retained the amorphous structure when the holding time is less than 20 min. The surface area fraction of oxide film on the interface of joints was detected by ultrasonic inspection. Moreover, the surface area fraction of oxide film is in excellent agreement with the theoretical value calculated by shear strength. The result indicated that surface oxide film is the dominant barrier on the diffusion bonding of bulk metallic glass rather than low atomic diffusion coefficient.

关键词： Bulk metallie glass Diffusion Surface Diffusion bonding Oxide film

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Modular multilevel converter with full-bridge submodules and improved low-frequency ripple suppression for medium-voltage drives

Modular multilevel converter with full-bridge submodules and...

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Annual IEEE Conference on Applied Power Electronics Conference and Exposition (APEC)

作者： Liqun He Kai Zhang Jian Xiong Shengfang Fan Yaosuo Xue State Key Laboratory of Advanced Electromagnetic Engineering and Technology (AEET) Huazhong University of Science and Technology Wuhan China Huazhong University of Science and Technology Wuhan Hubei CN Corporate Technology Siemens Corporation Princeton NJ USA

ISBN: (纸本)9781479967360

Due to the low-frequency voltage fluctuation problem, application of modular multilevel converters (MMC) in wide-speed-range medium-voltage (MV) drives is still difficult. This paper proposes a new approach to this problem. Firstly, full-bridge submodules (FB-SM) are used in place of the traditional half-bridge submodules (HB-SM). The former can significantly reduce the low-frequency pulsating power in the SM capacitors. Secondly, an improved “square wave plus third-order harmonic injection” with quasi-resonant (QR) control scheme is proposed to transfer the low-frequency ripple power into high-frequency ones. Simulation and experimental results prove the validity of proposed method. A comparison between the FB-SM based and HB-SM based MMCs showed good potential of the former in MV drive applications.

关键词： Capacitors Fluctuations Voltage fluctuations Harmonic analysis Stators Torque Frequency control

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Traveling-wave-based fault location in electrical distribution systems with digital simulations

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Telkomnika (Telecommunication Computing Electronics and Control) 2014年第2期12卷 297-304页

作者： Tang, Jinrui Yin, Xianggen Zhang, Zhe State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Luoyu Road 1037 Wuhan 430074 Hubei Province China

Traveling-wave-based fault location in electrical distribution systems is an important safeguard for the distribution network reliability. The effectiveness of the methods is verified directly in power grid in the early stages, while different fault types can't appear in a short time. And normal dynamic physical simulation cannot meet the teaching demand either because of the limitation of transmission line model and other factors. So PSCAD/EMTDC and MATlab are used to illustrate the the fault location methods in this paper, which can promote the traveling-wave-based fault-location technology. Meanwhile, the traveling-wave-based fault-location method based on characteristic frequencies is analyzed in this paper.

关键词： Electric lines

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LCL Type Grid-connected Converter no Startup Inrush Current Control Method Based on Capacitor Branch Voltage Feedforward

LCL Type Grid-connected Converter no Startup Inrush Current ...

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Annual Conference of the IEEE Industrial Electronics Society

作者： Shiying Zhou Xudong Zou Donghai Zhu Yong Kang Li Tong Xiaolu Gao State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Zhejiang Electric Power Corporation Research Institute China-EU Institute for Clean and Renewable Energy Huazhong University of Science and Technology

ISBN: (纸本)9781479917631

Dual-loop PI control strategy for LCL type grid-connected converter is usually used in wind power generation. Serious inrush current will be caused when grid-connected converter runs on the rectified status at the start time if no effective control strategy is taken, so it is necessary to improve the startup control performance and the grid voltage feedforward method is usually used. However, in wind power generation, the grid voltage of the transformer's high voltage side can't be directly sampled. To deal with it, a method is proposed based on the feedforward of filter capacitor branch's voltage. Firstly, the mathematical model of LCL type grid-connected converter, under the synchronous rotating reference frame, is established. And the cause of inrush current at the rectified start time of grid-connected converter is analyzed in detail. Then, the feedforward of capacitor branch's voltage is introduced into the output of current loop, and the theoretical analysis on its effectiveness of inrush current suppression is made. Finally, the simulation analysis based on the 10kW LCL type grid-connected converter and the experiments based on the 10kW direct drive wind power grid-connected converter prototype are carried out. The results verify that this method can effectively suppress startup inrush current and improve dynamic response of the grid current control.

关键词： LCL type grid-connected converter Startup inrush current Voltagefeedforward Windpower generation

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R&D on Dummy Load Prototype for ITER Coil Power Supply System

R&D on Dummy Load Prototype for ITER Coil Power Supply Syste...

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IEEE Symposium on Fusion engineering

作者： C. Li M. Zhang K.X. Yu X. Q. Qin Z. Q. Song P. Fu State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Wuhan China School of Electrical Engineering and Automation Hefei University of Technology Hefei China Institute of Plasma Physics Chinese Academy of Science Hefei China

This paper mainly introduces the research and development (R&D) of the dummy load prototype, whose functions are to verify the capability of the ITER magnetic power supply systems to operate at their rated power levels without energizing the superconducting coils. The rated inductance is 6.73 mH and the extreme pulse operation mode is 68 kA/15 s on and 900 s off. Therefore, in order to meet the special requirements of the large inductance and the thermal and dynamic stability, a new structure of dry-type air-core watercooling prototype with epoxy resin casting technique is presented, which has a higher energy density in comparison with the traditional structures. The finite-element simulation analysis is introduced in detail, focusing on the thermal performance of coil and water-cooling system during the whole operation and the dynamic stability, especially under the extreme pulse operation condition. In addition, the electromagnetic environment (EME) around the dummy load is also analyzed under normal and pulse operation, which is the input for the instrumentations selection and the delimitation of personal safe area.

关键词： dummy load finite-element thermal dynamic stability seismic

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Design of an electron gun for terahertz radiation source

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Chinese Physics C 2014年第4期38卷 93-97页

作者：李骥裴元吉胡桐宁陈曲珊冯光耀尚雷李成龙 National Synchrotron Radiation Laboratory University of Science and Technology of China State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology Deutsches Elektronen-Synchrotron

An EC-ITC （External-Cathode Independently Tunable Cells） RF gun was employed with the aim of obtaining short-pulse bunches with high peak current for a terahertz radiation source. A gridded DC gun plays a key role as the external injecting electron source of the ITC RF gun, the performance of which determines the beam quality in the injector and transport line. In order to make the beam well compressed in the ITC RF gun, the energy of the electrons acquired from the gridded DC gun should be 15 keV at most. A proper structure of the gridded gun with double-anode is shown to overcome the strong space- charge force on the cathode, which is able to generate 6 μs beam with 4.5 A current successfully.

关键词： gridded DC gun RF gun EC-ITC

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Finding shortest lattice vectors in the presence of gaps

Finding shortest lattice vectors in the presence of gaps

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RSA Conference Cryptographers’ Track, CT-RSA 2015

作者： Wei, Wei Liu, Mingjie Wang, Xiaoyun State Key Laboratory of Information Security Institute of Information Engineering Chinese Academy of Sciences Beijing China Institute for Advanced Study Tsinghua University Beijing China Beijing Research Institute of Telemetry Beijing China Key Lab of Cryptologic Technology and Information Security Ministry of Education Shandong University Jinan China

ISBN: (纸本)9783319167145

The λi-gap λi/λ1among the successive minima of a lattice especially its λ2-gap often provides useful information for analyzing the security of lattice-based cryptographic schemes. In this paper, we mainly study the efficiency of shortest vector problem (SVP) algorithms for lattices with λi-gap. First, we prove new upper bounds for the packing density of this type of lattices. Based on these results, we discuss the efficiency of the ListSieve-Birthday algorithm proposed by Pujol and Stehĺe for SVP, and obtain the conclusion that the complexity will decrease obviously as the λi-gap increases. Particularly, ListSieve- Birthday becomes faster than the current best deterministic (Voronoi cell-based) algorithm for SVP, as long as λ2-gap is larger than 1.78. When λ2-gap is up to 28, the time complexity is 20.9992n+o(n), and the coefficient factor of n is approximately to 0.802 if λ2-gap is large enough. Moreover, we provide an SVP approximation algorithm modified by the ListSieve-Birthday algorithm. This algorithm terminates sieve process earlier and relaxes the birthday search, and hence decreases the time complexity significantly. © Springer International Publishing Switzerland 2015.

关键词： Approximation algorithms

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Finite Element Method Applied to Fuse Protection Design

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Plasma Science and technology 2014年第3期16卷 294-299页

作者：李森宋执权张明许留伟李金超傅鹏王敏董琳 College of Electrical and Electronic Engineering Huazhong University of Science and Technology State Key Laboratory of Advanced Electromagnetic Engineering and Technology Institute of Plasma Physics Chinese Academy of Sciences China International Nuclear Fusion Energy Program Execution Center

In a poloidal field （PF） converter module, fuse protection is of great importance to ensure the safety of the thyristors. The fuse is pre-selected in a traditional way and then verified by finite element analysis. A 3D physical model is built by ANSYS software to solve the thermal- electric coupled problem of transient process in case of external fault. The result shows that this method is feasible.

关键词： PF converter thyristor protection fuse verification finite element method

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Research on fast solid state DC breaker based on a natural current zero-crossing point

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Journal of Modern Power Systems and Clean Energy 2014年第1期2卷 30-38页

作者： Wang XIANG Yu HUA Jinyu WEN Meiqi YAO Naihu LI State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and TechnologyWuhan 430074China Alstom Grid China Technology Center(CTC) Minhang DistrictShanghai 201114China

The DC fault characteristics of voltage source converter based high voltage direct current(VSC-HVDC)systems are analyzed in this *** phenomenon whereby the capacitor on DC side discharges quickly during a DC fault contributes to a large short-circuit fault *** traditional DC breakers nor DC switches can cut off the fault current under this condition.A fast solid state DC breaker design method is proposed in this *** method is based on the fault current characteristics of the inverter in multi-terminal HVDC systems(MTDC),where a fault current appears at the natural zerocrossing point near the *** this point,by coordinating the AC breakers near the rectifier,the DC breaker could reliably cut off the DC fault current and protect the system.A detailed model for this fast solid state DC breaker and its operation sequence are studied,based on this design *** modeling a five-terminal meshed DC grid and a fast DC breaker were carried out with PSCAD/EMTDC using this design *** results from the simulations confirmed the validity of the design method.

关键词： VSC-HVDC Multi-terminal HVDC DC short circuit fault DC breaker

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Operating Parameters Optimization of SMES Considering Transient Thermal Stability

Operating Parameters Optimization of SMES Considering Transi...

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IEEE International Conference on Applied Superconductivity and electromagnetic Devices

作者： Kang Gong Jing Shi Li Ren Yin Xu Yi Zhang Yang Liu Li Hui Zhang Xiao Zhou Ao Bo Zhou State Key Laboratory of Advanced Electromagnetic Engineering and Technology Huazhong University of Science and Technology

ISBN: (纸本)9781467381086

In this paper, an operating parameters optimization method for SMES considering transient thermal stability is proposed. Firstly, based on the analysis of transient thermal characteristics of SMES, a neural network based transient thermal analysis model is established to test the transient thermal stability of SMES for particular application scenarios. Then, based on the proposed model, a procedure is designed to find the best operating parameters of SMES, which can maintain the transient thermal stability of HTS magnet and meet the demand of power system as far as possible. Finally, the effectiveness of operating parameters optimization for SMES are verified by co-simulation based on MATlab and COMSOL.

关键词： Component SMES Reliability Transient thermal stability Current maintain

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