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11th International Conference on Electrical Machines and systems, ICEMS 2008

作者： Yi, Lei Zhengming, Zhao Jing, Xue State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing 100084 China

ISBN: (纸本)9787506292214

Three-phase induction motors as well as power converters are intrinsically efficient machines and devices. However, due to the common misapplication of them with loads like pumps and fans, these electric machine systems are considered a great potential of energy conservation in industries. As to assessing methods of energy conservation, neither the study of induction machine efficiency nor the analysis of pumps and fans performance is new. However, the systematic and qualitative analysis and assessment of the energy efficiency of induction machines, loads and control devices acting as a whole system are still complicated yet indispensable for electric machine system energy conservation program in China. In this paper, a systematic and qualitative assessment method for energy application efficiency of electric machine system is raised. Based on this method, an assessing computer program is designed to provide referencing information for making investment decisions regarding energy efficiency measures at manufacturing plants. An expert system is also designed to choose equipments that match each other.

关键词： Investments

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Effect of surface topography and morphology on space charge packets in polyethylene

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Journal of Physics: Conference Series 2009年第1期183卷

作者： Zhou Yuanxiang Wang Yunshan Wang Ninghua Sun Qinghua State Key Lab of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing 100084 China China Electric Power Research Institute Haidian District Beijing 100085 China

Polyethylene (PE) is a major kind of internal insulating material. With great progresses of space charge measurement technologies in the last three decades, lots of researches are focused on space charge in PE. The heat pressing and annealing condition of polyethylene affect its morphology obviously. During the heat pressing, the surface of PE forms different surface topographies because of different substrate materials. Surface topography has great relation to the epitaxial crystallization layer and influences the space charge characteristic of PE dramatically. This paper studied the formation process of different surface topographies and their micrographic characters in low density polyethylene (LDPE). pulsed electro-acoustic (PEA) method was used to measure the space charge distribution of samples with different surface topographies and morphologies in LDPE. The effect of surface topography and morphology to space charge packet were studied. The surface topography has great influence on space charge packet polarity and morphology has influence on both movement speed rate and polarity of space charge packet.

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Analysis of electrical tree ageing in silicone rubber by physicochemical approach

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Journal of Physics: Conference Series 2009年第1期183卷

作者： Y X Zhou Q Nie Z Z Chen R Liu State Key Lab of Control and Simulation of Power Systems and Generation Equipments Department of Electrical Engineering Tsinghua University Beijing 100084 China Department of Electrical Engineering Zhengzhou University Zhengzhou 450001 China

In this paper, the characteristics of electrical tree ageing in silicone rubber (SIR) under AC voltage were studied. The electrical tree initiation rate is 20% after the application of 6 kV AC voltage for 1000 hours. Samples are separated into three kinds according to processes of electrical tree formation: virgin samples without voltage application, non-treed samples without electrical tree formation after 1000 hours and treed samples with electrical tree formation after 1000 hours. Certain physicochemical diagnostic tests were carried out to understand the degradation of material, ascribed to long-time voltage application, using differential scanning calorimetry (DSC) and thermogravimetric-differential thermal analysis (TG-DTA). Physicochemical analyses, especially the DSC results, show that no additional phases are formed in the processes of electrical tree ageing in SIR. Reduction of the melting point and crystallinity of SIR is observed in the sequence of virgin samples, non-treed samples and treed samples. The activation energy values were calculated from the TG-DTA data. Compared to virgin samples, obvious reduction of activation energy value is observed in non-treed samples. Degradation in SIR has already occurred before electrical tree formation and charge injection and extraction by high field electrode under AC voltage is regarded as the reason.

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DC/DC Converter Applied in the Photovoltaic- Inclined Thermal Collector Hybrid systems for Brackish Water Desalination

DC/DC Converter Applied in the Photovoltaic- Inclined Therma...

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11th International Conference on Electrical Machines and systems(第11届国际电机与系统会议)

作者： Liqiang Yuan Mohamed Eltawil Zhengming Zhao Yaodong Lu State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department o State Key Laboratory of Control and Simulation of Power System and Generation EquipmentDepartment of

A chronic drinking water shortage is one of the most important issues in the developing countries, and drinking water from dirty water sources causes serious damage to inhabitants health in some remote areas. The solar distillation remains the most favorable process for the supplying of water to small communities. Base on the traditional solar still, an improved hybrid photovoltaic/thermal (PVT) desalination system is presented. The PV modules that are combined with thermal units, constitute the PVT systems which has longer operating time and higher average fresh water production. This paper introduces the DC/DC converter applied in this type of systems, including its structure and control strategy which is suitable for PV array and driving supportive heater. The experimental results for the converter and the whole system are showed and analyzed.

关键词： DC-DC power converters Photovoltaic systems Solar power generation Desalination Temperature Water resources Hybrid power systems Solar energy Water heating power system simulation

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A Novel Direct power control Strategy for Three-Level PWM Rectifier Based on Fized Synthesizing Vectors

A Novel Direct Power Control Strategy for Three-Level PWM Re...

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11th International Conference on Electrical Machines and systems(第11届国际电机与系统会议)

作者： Ting Lu Yongchang Zhang Yingchao Zhang Zhengming Zhao Liqiang Yuan State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department o State Key Laboratory of Control and Simulation of Power System and Generation EquipmentDepartment of

A novel direct power control (DPC) strategy for three-level neutral-point-clamped (NPC) pulse-width-modulation (PWM) rectifier, based on fixed synthesizing vectors, is proposed in this paper. The strategy breaks through the restrictions of vector switching with a simple switching table, improves the excellent dynamic performance of DPC, avoids the neutral-point voltage unbalance and the excessive voltage jumps in phase and line-to-line voltages of the rectifier, and guarantees the proper minimum pulse width and switching intervals between switches in different phases simultaneously. Experimental results verify the validity and feasibility of the proposed scheme.

关键词： Pulse width modulation power control Rectifiers Space vector pulse width modulation Switches Thyristors Topology Voltage control Snubbers control system synthesis

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Instantaneous energy balancing in three-level neutral point clamped converters

Instantaneous energy balancing in three-level neutral point ...

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IEEE Conference on Vehicle power and Propulsion (VPPC)

作者： Lu Ting Zhengming Zhao Liqiang Yuan Shuping Wang State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China. State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China

Instantaneous energy balancing plays an important role in power electronics conversion. The unbalance of electromagnetic energy not only debases the system performance but also decreases the reliability and efficiency of the conversion. In this paper, instantaneous energy balancing problems in three-level neutral point clamped (NPC) converters are classified and discussed. Typical examples and their usual solutions of each kind of problems are expounded and compared. In the end of this paper, limitations and disadvantages of traditional methods are analyzed, and electromagnetic field method is summarized as the new trend to analyze electromagnetic energy transmission and exchange. The method using electromagnetic field theory is emphasized to be the better approach to solve the aforementioned energy balancing problems.

关键词： Voltage control Capacitors Open loop systems Pulse width modulation converters power electronics Energy storage Switching converters power system simulation power system reliability Electromagnetic analysis

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Investigation and analysis of the influence of magnetic wedges on high voltage motors performance

Investigation and analysis of the influence of magnetic wedg...

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2008 IEEE Vehicle power and Propulsion Conference, VPPC 2008

作者： Wang, Shuping Zhao, Zhengming Yuan, Liqiang Wang, Buyao Department of Electrical Engineering State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China Anhui Electric Power Research Institute Corporation Company Ltd. Department of XiangTan Electric Machine Xiangtan China

ISBN: (纸本)9781424418497

To weaken the pulsation of the harmonic magnetic field and improve the wave of the air-gap magnetic field in high voltage motors because of their open slots, magnetic slot wedge should be imbedded into the slot opening. In the paper, through analyzing the air-gap magnetic field distribution of large-scale motors affected by embedding magnetic slot wedges in open slots, the influence of magnetic slot wedge on the motor parameters and performance is discussed in theory. The finite element analysis (FEA) and the experiment results were given, which not only proves the validity of the analysis in the paper, also through the simulation results the proper parameters of magnetic slot wedges for best performance of motors were concluded, which provides a theoretical reference for the manufacturers when choosing or processing magnetic slot wedges. © 2008 IEEE.

关键词： Finite element method

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Design and control of a Three-Phase Grid-Connected Photovoltaic System with Developed Maximum power Point Tracking

Design and Control of a Three-Phase Grid-Connected Photovolt...

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23rd Annual IEEE Applied power Electronics Conference and Exposition (APEC 2008), vol.2

作者： Zhou Dejia Zhao Zhengming Mohamed Eltawil Yuan Liqiang The State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing China

In this paper an optimum design and control of three-phase grid-connected PV system has been proposed and analyzed. Also, a developed maximum power point tracking (MPPT) controller that uses the PV array differential power to voltage (dP/dV) as an index to provide the reference voltage of maximum power point (MPP) quickly and accurately is presented. The control scheme of a three phase current-controlled space vector pulse-width modulation (SVPWM) inverter in rotating synchronous coordinate d-q with the proposed MPPT algorithm and feed-forward compensation is discussed. The PV grid-connected system controller employs multi-loop control with the filter inductor current of the inverter in the inner loop to achieve fast dynamic response and the outer loop to control dc bus voltage for MPPT. The design method provided in the paper for the controller parameters and filter proved to be very practical and effective. Both the power quality into the grid and power factor correction comply with standards IEEE 929-2000. Good agreement is obtained between simulation and experimental results which illustrated the high performance of the proposed approach.

关键词： Digital signal processor Grid-connected PWM inverter MPPT Photovoltaic (PV) system PI compensators Unity power factor

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Intelligent controller for LEDs lighting systems supplied by batteries

Intelligent controller for LEDs lighting systems supplied by...

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IEEE Conference on Vehicle power and Propulsion (VPPC)

作者： Bo Feng Zhengming Zhao Yingchao Zhang Dejia Zhou Liqiang Yuan State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China

LED lighting system supplied by batteries is one of effective solutions to vehicle and photovoltaic lighting systems. In order to improve lighting performance and prolong the life of LEDs and batteries, this paper proposes a novel intelligent controller for LED lighting systems. Stage constant current (SCC) control strategy is proposed, which determines the optimal working current of LEDs (I ref ) according to their ambient temperature and the capacity of batteries. For implementing SCC control strategy, a new control algorithm of double current loops and feedforward (DCLF) control is proposed based on Boost converter with constant current source. Both output current and inductor current are used as feedback control variables and input voltage is employed as feedforward compensation in the proposed algorithm. simulations have been conducted using PSIM software; and based on that, a 50 W photovoltaic LED lighting system has been developed to implement a serial of comparative experiments. The results show the advantages and validity of DCLF algorithm, such as excellent dynamic performance and good robustness.

关键词： Lighting control control systems Light emitting diodes LED lamps Photovoltaic systems Solar power generation Battery powered vehicles Optimal control Temperature control Inductors

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A novel Modbus RTU-based communication system for adjustable speed drives

A novel Modbus RTU-based communication system for adjustable...

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IEEE Conference on Vehicle power and Propulsion (VPPC)

作者： Hu Sideng Zhao Zhengming Zhang Yingchao Wang Shuping State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China

ISBN: (纸本)9781424418480

The communication protocol is important for applying adjustable speed drive (ASD) systems to an industry network. This paper proposes a novel scheme of communication system for the ASD system based on Modbus protocol. The most remarkable advantage of the approach lies in the tradeoff between performance and economic cost for a power converter system. The overall system is built on master-slave structure and easy for interacting with other networks. An additional study on the cyclic redundancy check (CRC) in Modbus RTU is introduced to obtain the optimization design in the actual application and the optimization method in software design is also presented. The performance of the communication system obtained from experiment conducted on the 15 kW ASD system validates the effectiveness of the proposed design method.

关键词： Variable speed drives Protocols Cyclic redundancy check Communication industry power system economics power generation economics Costs Master-slave Design optimization Application software

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