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IEEE International Symposium on Power Electronics for Distributed Generation systems (PEDG)

作者： Fanbo He Zhengming Zhao Ting Lu Liqiang Yuan State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing China

DC voltage control is critical for grid-connected inverters, as it contributes to reduce the DC capacitance and improve system reliability as well as MPPT performance. A predictive control scheme of DC voltage for single-stage three-phase grid-connected PV inverters is proposed based on the analysis of the energy balance relationship in one control period, while AC current is also regulated by predictive control. The proposed scheme provides both good dynamic and steady-state performance. The dynamic response is especially excellent. The DC voltage is adjusted as fast as possible with little overshoot.

关键词： Voltage control Inverters Voltage measurement Regulators Predictive control Steady-state Capacitance

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Modal analysis of wind turbine tower

Modal analysis of wind turbine tower

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World Non-Grid-Connected Wind Power and Energy Conference, WNWEC

作者： Jie Chen Dongxiang Jiang State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Thermal Engineering Tsinghua University Beijing China

As the support structure of wind turbine, the tower bears alternating loads of wind when the wind turbine runs. To ensure the reliability of the wind turbine, it's necessary to carry out modal analysis on the tower, and this would prevent the natural frequency of the tower close to the rated speed of wind turbine. In this paper, finite element analysis of the tower is solved using ANSYS, and the natural frequencies and modes of the tower are presented. After comparing the results of three models, a simple model for modal analysis, which can be calculated in short time, is finally determined.

关键词： Poles and towers Wind turbines Modal analysis Finite element methods Analytical models Material properties Solid modeling

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Application of back propagation neural network to fault diagnosis of direct-drive wind turbine

Application of back propagation neural network to fault diag...

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World Non-Grid-Connected Wind Power and Energy Conference, WNWEC

作者： Xueli An Dongxiang Jiang Shaohua Li State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Thermal Engineering Tsinghua University Beijing China

The vibration signals of wind turbines are highly nonlinear and non-stationary due to wind turbine operation conditions that are very complicated. The signals will be more complex when a fault occurs. Aiming at these problems, a fault diagnosis method for direct-drive wind turbine is presented based on back propagation neural network (BPNN). The time-domain feature parameters of vibration signals in the horizontal and vertical direction are considered in the method. Five experiments of direct-drive wind turbine with normal, wind wheel mass imbalance, wind wheel aerodynamic imbalance, yaw and blade break are carried out in laboratory scale. Through analyzing the features of five conditions, the time-domain feature parameters in horizontal and vertical direction of the vibration signal are selected as the input samples of BPNN. By training, the BPNN model can be constructed between feature parameters and fault types. The validity of the BPNN model is verified using test samples. The results indicate that the proposed method has higher diagnostic accuracy. It can used in on-line fault diagnosis of direct-drive wind turbines.

关键词： Wind turbines Vibrations Fault diagnosis Artificial neural networks Blades Wheels Time domain analysis

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Current sharing of IGBT modules in parallel with thermal imbalance

Current sharing of IGBT modules in parallel with thermal imb...

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IEEE Energy Conversion Congress and Exposition, ECCE

作者： Xuesong Wang Zhengming Zhao Liqiang Yuan State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing China

For large current, switching devices such as MOSFET and IGBT, often have to be connected in parallel. Due to this reason, derating and preselection of the switching devices become necessary to develop high-power converters. The current imbalance can be produced by stray inductances, device characteristic difference or asymmetric circuit. Moreover, thermal imbalance is another important reason for current balancing. The static and transient characteristics of an IGBT vary sensitively with its junction temperature. This paper focuses on the current sharing of IGBTs in parallel with thermal imbalance. In this paper, an active gate control method which can achieve current balancing of the IGBTs in parallel with thermal imbalance, is explained and verified by experiments. This method can be applied to an actual 160kW/380V power electronics converter prototype for improving the utilization of the switching devices and enhancing system reliability.

关键词： Insulated gate bipolar transistors Junctions Temperature measurement Temperature Temperature control Logic gates Transient analysis

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Reaction kinetics and mechanism of biomass pylolysis in a micro-fluidized bed reactor

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Journal of Fuel Chemistry and Technology 2010年第6期38卷 666-672页

作者： Jian YU Jian-hong ZHU Feng GUO Zheng-kang DUAN Yun-yi LIU Guang-wen XU State Key Laboratory of Multi-phase Complex System Institute of Process Engineering Chinese Academy of Sciences Beijing 100190 China Chemical Engineering Institute of Xiangtan University Xiangtan 411105 China School of Chemical Engineering Shenyang Institute of Chemical Technology Shenyang 110142 China

A Micro Fluidized Bed Reaction Analyzer (MFBRA) was used to study the pyrolysis of biomass in argon. Through on-line pulse feeding of reactant and continuously monitoring the composition changes of gas product, the MFBRA enables the measurement of reaction rates at arbitrary temperatures, the deduction of kinetic parameters and the analysis of reaction mechanism. By applying to biomass pyrolysis this article found that the pyrolysis reaction can finish in about 10 s, which is much shorter than the other literature values obtained in larger fluidized bed reactors but very close to the theoretically anticipated values. The detected evolving sequences of different gas species and the deduced kinetic parameters demonstrate further that the reactions between/among the formed different gas species in pyrolysis prevail to certain degree and there are different pathways for forming the different gas species. The activation energy and pre-exponential factor derived by treating the pyrolysis gas as a single product are 11.77 kJ/mol and 1.45 s −1 , which are obviously lower than the literature values measured in thermogravimetric analyzers.

关键词： micro fluidized bed reaction kinetics biomass pyrolysis

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Development and experimental verification of a mathematical expression for the discharge rate of a semi-circular open channel

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International Journal of Agricultural and Biological engineering 2010年第3期3卷 19-26页

作者： Qu Liqin Yu Xinxiao Xiao Juan Lei Tingwu The Key Laboratory of Modern Precision Agriculture System Integration Research College of Hydraulic and Civil EngineeringChina Agricultural UniversityBeijing 100083China Ministry of Education Key Laboratory of Soil and Water Conservation and Desertification Combating College of Soil and Water ConservationBeijing Forestry UniversityBeijing 100083China State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau Institute of Soil and Water ConservationShaanxi ProvinceYangling 712100China College of Hydraulic Science and Engineering Taiyuan University of TechnologyShanxi ProvinceTaiyuan 030024China

Semi-circular open channel plays an important role in various applications and the measurement of its discharge is of *** this study,theoretical formulae for free overflow in a semi-circular channel are developed and presented for the discharge and wetted area *** traditional discharge formulation and available experimental data are used to verify and validate the proposed *** discharges calculated by using the proposed relationship show very good agreement with the experimental data *** results from this study supply the basis for circular weir development.

关键词： verification discharge open channel flow weir circular wetted area measurement

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An Improved Auction Scheme for Task Allocation in Wireless Sensor Network

An Improved Auction Scheme for Task Allocation in Wireless S...

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International Conference on Wireless Communications, Networking and Mobile Computing (WiCom)

作者： Yukun Li Zhipeng Gao Yang Yang Qijian Xu Xuesong Qiu State Key Laboratory of Networking and Switching Technology Beijing University of Posts and Telecommunications Beijing China Beijing Institute of Electronic System Engineering Beijing China

Task allocation has been widely studied in high-performance computing environment. However, existing task allocation algorithms can not be directly applied to WSN because of the limited energy resources and computing capabilities of the Wireless Sensor Network (WSN). In this paper, we propose a new auction-based task allocation model for WSN and create an energy consumption based utility function to evaluate the allocation plan. Moreover, new policies are added into traditional auction scheme. simulation results show that the proposed improved auction mechanism of Multi-Agent system (MAS) auto-negotiation model is a real-time and effective scheme, which can be carried out to allocate tasks for WSN with a high success rate.

关键词： Wireless sensor networks Resource management Real time systems Energy consumption Sensor phenomena and characterization Ad hoc networks

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Long-term stability of frequency transfer over an urban fiber link using microwave phase compensation

Long-term stability of frequency transfer over an urban fibe...

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International Conference on Electromagnetics in Advanced Applications (ICEAA)

作者： Zhigang Zhang Dong Hou Peng Li Cheng Liu Jianye Zhao Circuit and System Laboratory Institute of Quantum Electronics State Key Laboratory of Advanced Optical Communication System and Networks School of Electronics Engineering and Computer Science Peking University Beijing China

We report a novel system for highly stable 100 MHz mode locked pulse as a reference frequency signal transfer through a round trip 20 km urban fiber link. An electronic approach for compensating the fluctuations introduced by the link is proposed and implemented. The rms phase fluctuation was reduced from 75 mrad (118 ps) to 4 mrad (6.3 ps) in 48 hours, and the frequency stability was improved by three orders of magnitude in the measurement time.

关键词： Optical fiber networks Optical fibers Fluctuations Optical pulses Fiber lasers Delay

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How multiple-dependency structure of classes affects their functions a statistical perspective

How multiple-dependency structure of classes affects their f...

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International Conference on Software Technology and engineering (ICSTE)

作者： Yutao Ma Keqing He Bing Li Xiaoyan Zhou Postdoctoral Workstation Institute of Electronic System Engineering Beijing China State Key Laboratory of Software Engineering Wuhan University of China Wuhan China

Networks have been considered an effective tool to describe the topological structure of software. Recently, many object-oriented software systems were found to share global network features such as scale free and small world. In this paper, we defined a special structural feature of individual class to investigate the relationship between external structure and internal function. The metric (m) takes in-degree and reachable set of nodes in class-level dependency graphs derived from source code into consideration. Experimental results show that (1) the distribution of frequency-of-occurrence of m roughly follows a power-law distribution, and (2) there is a weak but distinct positive correlation between m and either WMC or LCOM, and classes with complex multiple-dependency structure have on average more complicated functions (and less cohesion) than other classes within specific groups classified by m. Thus, the metric could be a useful complementary measure for traditional OO metrics to analyze the complexity, stability and maintainability of classes.

关键词： Measurement Software systems Correlation Couplings complexity theory Java

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state of the art of hybrid excitation permanent magnet synchronous machines

State of the art of hybrid excitation permanent magnet synch...

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作者： Wang, Shanming Xia, Yonghong Wang, Xiangheng Su, Pengsheng Huang, Shaogang Zhang, Anming State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing 100084 China Department of Electrical and Automatic Engineering Nanchang University Nanchang Jiangxi 330031 China Military Deputy Department Dalian 426 Factory No.1 Yanhai Jie Xigang Qu Dalian Liaoning 116005 China

ISBN: (纸本)9788986510119

The hybrid excitation permanent magnet machine (HEPMM) combines two kinds of excitation: permanent magnet (PM) and electrical excitation, so it possesses the advantages of PM machines and overcomes the incapability of regulating the excitation field. By now many HEPMM schemes have been presented. In this paper the operation principle, structure, advantages and disadvantages of these HEPMMs have been reviewed and compared in detail. These HEPMMs are classified into three types by new classification method - placement of PM and iron poles. At last novel harmonic excitation HEPMM is proposed and discussed.

关键词： Permanent magnets

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