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IEEE Energy Conversion Congress and Exposition, ECCE

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

The discrete control technology for AC machine drives is widely applied in the industrial field. This paper aims to excavate new approaches to enhance the discrete control system in AC motor drive systems from following aspects: matching design for discrete subsystems, synchronization in the signal processing and dealing with the restrictions in the voltage output. The proposed approaches are incorporated with three key techniques applied in high performance induction motor drive systems: DC pre-excitation, parameter identification and flux observer with a sensorless control to verify the feasibility. The anti-interference and synchronization procedure in the implementation are also proposed. The experimental results from the test on 55kW/400V and 160kW/400V ASD (Adjustable Speed Drives) systems validate the effectiveness of the proposed approaches.

关键词： Switches Variable speed drives Observers Parameter estimation Pulse width modulation Induction motors

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Design and implementation of the high efficiency photovoltaic system with solid state lighting

Design and implementation of the high efficiency photovoltai...

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International Conference on Electrical Machines and systems (ICEMS)

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

Photovoltaic application of LED lighting has been a hot trend in residential illumination, for it integrates the advantages of both the PV systems and LED lights. However, it has a series of problems, such as high thermal loss, poor reliability, and a short life span. To address these problems, this paper presents a deep research on the whole system from a low-cost, high-efficiency and long-life point of view. A main circuit integrating maximum power point tracing (MPPT) control and battery management, as well as a double-loop control for LED load is developed. A set of protection system is applied to ensure high reliability of the system. The control strategies are tested on the demonstrator and prove to be effective.

关键词： Light emitting diodes Batteries Discharges MOSFET circuits Lighting Photovoltaic systems Snubbers

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Experimental investigation and analysis for gearbox fault

Experimental investigation and analysis for gearbox fault

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

作者： Shaohua Li Dongxiang Jiang Minghao Zhao State Key Laboratory of Control and Simulation of Power System and Generation Equipment Department of Thermal Engineering Tsinghua University Beijing China

As an important component of a wind turbine drive chain, the high failure rate of the gearbox can have a serious impact on the operation of wind turbine units. The fault diagnosis of the gearbox is therefore important for the safety of wind turbine units. In this paper, a gearbox experiment rig was built, experiments on the gear surface spalling fault were held on the rig under laboratory conditions, the shaft vibration displacement signals were collected, related vibration signals were analyzed by time domain, amplitude domain, frequency domain and wavelet analysis, and the results of different analysis methods were compared. The results show that the waveform of normal and fault signals are similar, the amplitude of the signals will change while the fault happens, and the wavelet analysis is more effective than frequency domain analysis on gearbox fault features extraction.

关键词： Shafts Spectrogram Gears Frequency domain analysis Wind turbines Amplitude modulation Feature extraction

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Vibration characteristics on a wind turbine rotor using modal and harmonic analysis of FEM

Vibration characteristics on a wind turbine rotor using moda...

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

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

A wind turbine rotor system containing blades has its own characteristics. The vibration characteristics of blades with special airfoil can influence the vibration characteristics of the rotor system. This paper analyzed the vibration characteristics of a wind turbine rotor including blades with two-dimensional airfoil. The Finite Element Method (FEM) is applied to establish the rotor model, with the purpose that the FEM can adjust complex blades airfoils and acquire the details of the blades vibration characteristics. The modal characteristics are extracted based on the wind turbine model established in the laboratory. Using harmonic analysis of FEM, the excitation forces on the blades caused by the stochastic wind load are imposed on the rotor model and the stable response of the rotor system is calculated using ANSYS. Then the vibration characteristics are analyzed and the characteristics of the harmonic response are studied under different phases of the circumferential and axial forces.

关键词： Blades Wind turbines Rotors Finite element methods Harmonic analysis Force Solid modeling

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A Review on Overvoltages in Microgrid

A Review on Overvoltages in Microgrid

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

作者： Shuiming Chen Hongqiao Yu Department of Electrical Engineering State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China

Now microgrid has aroused increasing attention due to energy sustainable development and the development of distributed generations (DG), such as micro-turbines, gas turbines, wind power, photovoltaic and fuel cells. This paper introduces the basic structure of microgrid and summarizes the overvoltages that can occur in microgrid, including ground fault overvoltages, resonant overvoltages, overvoltage related to voltage regulation, switching overvoltages of inner microgrid, transfer overvoltages from distribution network (such as lightning and switching overvoltages). By analysis, this paper obtains the following conclusion: resonant overvoltages and lightning stroke transfer overvoltages are the most serious for microgrid.

关键词： Surges Resonance Lightning Sustainable development Distributed control Wind turbines Wind energy Photovoltaic systems Solar power generation Fuel cells

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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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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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Predictive DC voltage control for three-phase grid-connected PV inverters based on energy balance modeling

Predictive DC voltage control for three-phase grid-connected...

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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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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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simulation of lightning strike in 2-D and 3-D with fractal theory and its application

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2010年第22期30卷 127-134页

作者： Xu, Wei Chen, Shui-Ming He, Jin-Liang State Key Lab. of Control and Simulation of Power Systems and Generation Equipments Dept. of Electrical Engineering Tsinghua University Haidian District Beijing 100084 China

Lighting causes great damage to power systems due to the stochastic nature of lightning discharges and the vulnerability of lightning leaders to various environments in the process of inception and propagation. In this work, the growth of diffusion limited aggregation (DLA) was adopted for reproducing branches and tortuosity of lightning channels in both 2-D and 3-D simulations. By comparing the fractal dimensions of natural lightning discharges and simulation results on various discharge settings, we discovered that a fractal coefficient η = 2 can deliver a credible model of lightning strikes. We further proved the consistency between simulation results and observations conducted in Japan during 2005 and 2006 winter seasons on lightning strikes to a windmill and its lightning-protection tower. But the credibility of the result needs to be verified by further experimental data, when the model extended from 2-D to 3-D. Moreover, striking probability and the shielding effect in the actual condition were analyzed with the proposed simulation model. © 2010 Chin. Soc. for Elec. Eng.

关键词： Fractal dimension

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