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Effects of nonlinear gradient index on radiative heat transfer in a one-dimensional medium by the DRESOR method

Journal of Physics: Conference Series 2012年第1期369卷

作者： Z C Wang Q Cheng G H Wang Z F Huang H C Zhou State Key Laboratory of Coal Combustion Huazhong University of Science and Technology Wuhan 430074 Hubei People's Republic of China State Key Laboratory of Control & Simulation of Power System & Generation Equipment Department of Thermal Engineering Tsinghua University Beijing 10084 P. R. China To whom any correspondence should be addressed

The DRESOR (Distribution of Ratios of Energy Scattered by the medium Or Reflected by the boundary surface) method is applied for radiative heat transfer in a one-dimensional medium with a nonlinear gradient index and gray boundary surfaces. In this proposed method, the DRESOR values calculated by the Monte Carlo method express quantitatively the impact of scattering on radiative transfer and the radiative intensity with high directional resolution of high precision can be easily obtained. With given media characteristics and boundary conditions, the temperature and radiative flux distributions inside the medium are calculated under the condition of radiative equilibrium. It is shown, in the cases studied, that the DRESOR method has a good accuracy. The temperature distributions have a node with different kinds of sine changed gradient index distributions under the same boundary emissivity. The impact of the gradient index on the radiative heat transfer is considerable, and the same as that of the ratios of its amplitude and average index. Besides, the effects of optical thickness, boundary emissivity and scattering phase function on radiative transfer also should be paid adequate attention.

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A predictive DC voltage control scheme for back-to-back converters based on energy balance modeling

A predictive DC voltage control scheme for back-to-back conv...

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International Conference on Electrical Machines and systems (ICEMS)

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

This paper presents a predictive control scheme of DC-link voltage for back-to-back converters based on energy balance modeling. Since the variation of DC-link voltage is affected by the energy mismatch between rectifier and inverter, the energy distribution in a rectifier-inverter is analyzed. Moreover, in order to calculate the input and output energy in one control period accurately, the grid current is regulated by predictive control and the instantaneous active power consumed by the induction motor is estimated. Then, an equation based on energy balance in one control period is established, and the DC-link voltage can be controlled by solving it. Finally, simulation results show that with the proposed control scheme, the back-to-back converter exhibits both good dynamic and steady-state performances.

关键词： Voltage control Induction motors Rectifiers Capacitors Vectors Pulse width modulation Inverters

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Optimal design of the back-to-back IGBT-based converter with the concept of systematic safe operating area

Optimal design of the back-to-back IGBT-based converter with...

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International Conference on Electrical Machines and systems (ICEMS)

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

The key parameters of SOA (safe operating area) of semiconductor devices are hard to be measured when converter is operating, which is not helpful to protect converter at any time. On the other hand, surplus estimating method is widely used to design the main circuit. In order to guarantee the whole system works safely and improve utilization rate of devices, the concept of SSOA (systematic safe operating area) is presented. By determining the relationship of key parameters between devices and converter, the expression of SSOA is described quantitatively. Then it is implemented as a basic rule to design a back-to-back converter based on IGBT for 55kW induction motor optimally. Rated value of DC-link voltage and grid filter of the system is obtained reasonably as well.

关键词： Inductance Insulated gate bipolar transistors Rectifiers power harmonic filters Semiconductor optical amplifiers Induction motors

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A parallel based real-time electromagnetic transient simulator for IPS

A parallel based real-time electromagnetic transient simulat...

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IEEE Electric Ship Technologies Symposium, ESTS

作者： Yuan Gong Laijun Chen Ying Chen Yin Xu State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing China

IPS has many special characteristics, such as using multi-phase, multi-frequency and hybrid AC/DC devices. As a result, existing electromagnetic transient simulators developed for power systems on land do not apply to IPS. This paper aims to build up a parallel based real-time electromagnetic transient simulator for IPS. A fast multi-switching process method for parallel electromagnetic transient simulations is coined to handle the tremendous switch events in IPS. To solve the difficulties brought by multi-phase machines in IPS, a multilevel hybrid parallel algorithm is forged through the combination of component level and network level parallelization. Based on the key techniques mentioned above, a parallel simulator is built up. Through sufficient testing to typical examples of IPS, the accuracy and high-efficiency of the simulator are proved.

关键词： Computational modeling Switches Generators Real time systems Parallel algorithms Circuit faults Testing

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Design, simulation and analysis of the low stray inductance bus bar for voltage source inverters

Design, simulation and analysis of the low stray inductance ...

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International Conference on Electrical Machines and systems (ICEMS)

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

Hard-switching technique under the high voltage and high current is one of main trends of high power inverters. Under this switching mode, the stray parameters of the commutating loops, especially the stray inductance of the DC bus bar, have significant influence on the switching process, electromagnetic interference and component stress of the semiconductor switches. It becomes one of the key points for the safe operation of inverters. Based on an actual 55 kW inverter, the design, simulation and analysis for its bus bar is described in this paper. The bus bar model is built with the method of Partial Element Equivalent Circuit (PEEC), and the stray parameters are extracted from PEEC model and applied in the circuit simulation. Compared with the experimental results, the modeling validity is proved, and the simplified modeling process and design principles for complex physical bus bar are presented.

关键词： Integrated circuit modeling Equivalent circuits Inductance Inverters Capacitance Conductors Analytical models

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Lightning Overvoltage Suppression of power Transformer in UHV GIS by Ferromagnetic Ring

Lightning Overvoltage Suppression of Power Transformer in UH...

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第七届亚太防雷国际会议

作者： Xiao Zhang Jinliang He State Key Laboratory of Control and Simulation of Power System and Generation Equipments Department of Electrical EngineeringTsinghua UniversityBeijing 100084China

Lightning overvoltage protection is of great importance to the safety of UHV *** widely used arresters can only suppress the magnitude of lightning overvoltage but lack efficiency on alleviating the *** practice, insulation failure of UHV transformer is often reported.A new protection method is proposed in this paper using ferromagnetic ring as supplement to arresters to suppress lightning overvoltage in UHV ***, equivalent model based on the characteristic of ferromagnetic material and factual dimension of the ring is established for *** of an actual 1000kV GIS is carried out to thoroughly evaluate the lightning overvoltage suppressing effect of ferromagnetic rings with different materials and structure dimensions.

关键词： ferromagnetic ring lightning overvoltage UHV

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Comparison of Wind power Generation Interconnection Technology Standards

Comparison of Wind Power Generation Interconnection Technolo...

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IEEE PES Asia-Pacific power and Energy Engineering Conference (APPEEC)

作者： Jidong Wang Xuhao Du Xiaojing Zhang School of Electrical Engineering and Automation Key Laboratory of Power System Simulation and Control of Ministry of Education Tianjin University TJU Tianjin China

Smart Grid is one of the hot research directions of power system. How to interconnect the wind power generation with power system safely and reliably is a major challenge in the development of Smart Grid. Wind power generation interconnection standards are the technology base, which will push the development of smart grid. This paper compares the wind power generation interconnection standards of home and abroad mainly. It is pointed out the inadequacy of existing standards and that wind power generation interconnection standards should focus on power quality and low voltage ride through. This paper can be provided as a reference to improve existing standards and establish interconnection standards of other form new energy generation.

关键词： Standards Wind power generation Wind turbines Wind farms Smart grids

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Reactive power Optimization of power system based on Improved Particle Swarm Optimization

Reactive Power Optimization of Power System based on Improve...

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2011 4th International Conference on Electric Utility Deregulation and Restructuring and power Technologies(第四届电力设施管制、重建及能源技术国际会议 DRPT 2011)

作者： Hao Wang Huilan Jiang Ke Xu Guodong Li Key Laboratory of Power System Simulation and Control of Ministry of Education Tianjin University Ti Tianjin Electric Power Corporation Technology Center Tianjin 300384China

reactive power optimization is a nonlinear,multivariable,multi-constrained programming problem,which makes the optimization process *** this paper,based on the characteristics of reactive power optimization,a mathematical model of reactive power optimization,including comprehensive consideration of the practical constraints and reactive power regulation means for optimization,is *** particle swarm optimization (PSO) has been studied,and the method based on improved particle swarm optimization for reactive power is going to be taken in this *** for the IEEE 14-bus system proves that the improved PSO algorithm used in this paper for reactive power optimization is *** algorithm is simple,convergent and of high quality for optimization,and thus suitable for solving reactive power optimization problems,with some application prospect.

关键词： power system:Reactive power Optimization Artificial Intelligence Algorithms Particle Swarm Optimization

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Research on earthing schemes in LV microgrids

Research on earthing schemes in LV microgrids

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International Conference on Advanced power system Automation and Protection (APAP)

作者： BoTong Li YongLi Li Tao Ma Key Laboratory of Power System Simulation and Control of Ministry of Education Tianjin University 300072 China Junliangcheng Power Co. Ltd. China Huadian Tianjin 300300 China

For the access of green distributed generation(DG), LV microgrid is an important direction of development nowadays. Because the LV microgirds are in direct contact with users, so how to design its earthing scheme is the first thing to think about in order to guarantee personal safety and reliable operation of the equipments. Earthing schemes of LV mircrogrids are studied in the paper and how it works properly is presented. The principles of neutral earthing modes of microgrid is given according to standard IEC60364 and DGs neutral earthing mode is discussed under different operation modes. How the traditional protection modes of TN and TT are used in LV microgrids is studied. Considering the dispersion and variety of DGs and energy storage devices, combined earthing mode of TN and TT is proposed as a reasonable way for microgrids.

关键词： Grounding Conductors Buildings Earth Laboratories Automation

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A self-healing reconfiguration technique for smart distribution networks with DGs

A self-healing reconfiguration technique for smart distribut...

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International Conference on Electrical and control Engineering (ICECE)

作者： Dapeng Li Shouxiang Wang Jie Zhan Yishu Zhao Key Laboratory of Power System Simulation and Control of Ministry of Education Tianjin University Tianjin China State grid of china technology College Jinan Shandong China

The requirement for power supply reliability and power quality has been increasing. When a fault occurs in distribution networks, fast locating and isolating the fault, restoring the power, and reducing outage time and area are becoming more and more crucial. The concept of fast self-healing has been proposed, which is also the requirement for smart grid development. In this paper, a self-healing reconfiguration technique is proposed for smart distribution networks with insertion of distributed generations (DGs). And a tree structure algorithm based on heuristic rules is proposed. Islands formed by DGs are used to deal with fault isolation and power restoration after a fault occurs. The effectiveness of the proposed algorithm is verified using a 26 bus bars test system with DGs.

关键词： Reliability power system reliability Load flow Distributed power generation power quality

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