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Control strategy of VSC-HVDC in dual-infeed HVDC systems

Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2008年第7期28卷 97-103页

作者： Zhao, Cheng-Yong Sun, Ying Li, Guang-Kai Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Baoding 071003 China

Aim at the stability problem of multi-infeed direct current (MIDC) systems, voltage source converter based HVDC (VSC-HVDC) was applied to MIDC systems for improving the voltage characteristic of common AC bus in MIDC systems. A physical model of a dual-infeed HVDC and VSC-HVDC system was set up, and its mathematical model was developed. The rectangular coordinate form of VSC's power transmission equations was deduced through coordinate conversion. Based on the inverse system method for multivariable nonlinear control, the nonlinear controllers of VSC-HVDC system were designed. Simulation results performed on PSCAD/EMTDC show that the designed nonlinear controllers of VSC-HVDC can improve effectively the dynamic character of VSC-HVDC system, stabilize effectively the voltage of dual-infeed HVDC and VSC-HVDC system when AC side is disturbed, reduce the probability of commutation failure in the inverter of HVDC systems, and increase the operation reliability of HVDC systems.

关键词： HVDC power transmission

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dynamic state estimator based on WAMS during power system transient process

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2008年第7期28卷 19-25页

作者： Qin, Xiao-Hui Bi, Tian-Shu Yang, Qi-Xun Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Beijing 102206 China

As a measurement tool, wide area measurement system (WAMS) has the measurement error and bad data unavoidably. If the raw data is applied direcdy, the unpredictable consequence will be resulted in. Aiming at this problem, a novel dynamic state estimator for generator state variables is proposed. The mathematical model and the flowchart of the algorithm are described. Bad data detection and elimination approach is given as well. The simulation results show that the proposed method can provide the estimated trajectories of the generators in real-time, which eliminates the impact of measurement error and bad data and gives the backbone for WAMS based dynamic applications and real-time control.

关键词： Electric power systems

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PREDICTION ANALYSIS IN NONLINEAR systemS

PREDICTION ANALYSIS IN NONLINEAR SYSTEMS

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2008 International Conference on Machine Learning and Cybernetics(2008机器学习与控制论国际会议)

作者： YA-GANG ZHANG PO ZHANG ZENG-PING WANG Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry

The prediction analysis in nonlinear systems will be discussed carefully in this paper. We are mainly using CM (1,1) model to forecast data sequences, and the usual forecast precision is approximate to 90％. In this place we have found a generating rule that may realize chaotic synchronization at least in short and medium term, and we can analysis and forecast in this way. We hope to offer an effective prediction method to study certain properties of DNA base sequences, 20 amino acids symbolic sequences of protein structure, and the time series that can be symbolic in finance market et al.

关键词： Grey Prediction Chaotic Synchronization Symbolic dynamics Nonlinear system

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A Real-time Digital Simulation and Testing system for SVC Used in EAF power Supply system

A Real-time Digital Simulation and Testing System for SVC Us...

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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： Xinchun Shi Guoliang Zhou Chao Fu Weiwei Ma Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry

This paper introduced a real-time digital modeling approach for Electrical Arc Furnace (EAF) based on recorded field data. The model equaled the arc furnace to a current source controlled by the field data, and via adopting a phase locked technique, the synchronization between simulation and field data was performed, which made a long time real-time simulation possible. Besides, the model was used for evaluating the performance of SVC system which contributes to compensate Var and mitigate the harmonic and flicker caused by EAF. The simulation was implemented on the Real Time Digital Simulators (RTDS) and the results of simulation illustrate that the proposed EAF model and evaluation system can be used for testing a physical control system of SVC system and evaluating the control strategy.

关键词： arc furnace recorded field data real time digital simulation model close loop test

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Application of Phase-shifting Reactor in Harmonic Suppression of the Independent power Supply system

Application of Phase-shifting Reactor in Harmonic Suppressio...

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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： Lixia Zhou Qipeng Song Xiangning Xiao Zhongdong Yin Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry

The electric propulsive shipping power grid is a typical independent power supply system, and the anti-jamming ability to non-linear load is quit weak because of the limitation of generation capacity. So the influence of the harmonics becomes more serious. Meanwhile, the variation range of the voltage and frequency is often large, which can cause the tuning point deviation of the passive filter easily. A novel method to suppress the harmonics of this kind grid by adopting the phase-shifting strategy is put forward in this paper. The phase current can be divided into two branches through phase-shifting windings, and specific phase-shifting angle can be achieved by choosing proper winding turns and connection way. The configuration of the phase-shifting windings is analyzed in detail and the optimal selection of the phase-shifting angle is also done. The accuracy and the effectiveness are verified by the EMTDC/PSCAD based simulation results.

关键词： Inductors Harmonics suppression power supplies power harmonic filters power grids Mesh generation power generation Voltage Frequency Tuning

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dynamicAL COMPLEXITY OF A TYPICAL NONLINEAR system

DYNAMICAL COMPLEXITY OF A TYPICAL NONLINEAR SYSTEM

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2008 International Conference on Machine Learning and Cybernetics(2008机器学习与控制论国际会议)

作者： YA-GANG ZHANG ZENG-PING WANG HUI-FENG SHI XIAO-KUN WU Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control under Ministry

The dynamical complexity of a typical nonlinear system will be clarified in this paper. These stochastic symbolic sequences bear three features. The distribution of frequency, inter-occurrence times, the first passage time and the r-th passage time are discussed carefully. Especially, one introduces ordinal passage time and gives certain distribution functions in this typical nonlinear system. Finally, the visitation density function is obtained by Frobenius-Perron(F-P) operator P.

关键词： dynamical complezity Nonlinear system The first passage time Visitation density

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Calculation of circulating current in delta winding of transformers with Y, d connection

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Dianli Xitong Zidonghua/Automation of Electric power systems 2008年第24期32卷 60-64页

作者： Xia, Shiwei Zheng, Tao Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electricity Power University Beijing 102206 China

It is difficult to measure the circulating current in delta windings of Y, d connected transformer. So the current phase compensation has to be considered for transformer differential protection. In this study, a proportional relationship between the zero sequence current in Y winding and circulating current in delta winding is derived based on the differential equations of transformer. If phase A is closed exactly in 90 by controlled switching, the part of the line current of phase A is almost equal to the circulating current. By using the correlative formula, the correlative coefficient of line current of phase A and zero sequence current in Y side is calculated so as to distinguish parts of line current, with and without influence of inrush. Then the ratio between the zero sequence current and the circulating current, and the circulating current can be calculated as well. Finally the algorithm is verified with MATLAB and RTDS simulation. The results show that the calculated circulating current is identical with the actual one accurately, and it offers a new algorithm method for the differential protection and the equivalent transient inductance.

关键词： Winding

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Quantitative uncertainty analysis for power system dynamic simulation based on stochastic response surface method

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Dianli Xitong Zidonghua/Automation of Electric power systems 2008年第20期32卷 11-14+100页

作者： Han, Dong He, Renmu Ma, Jin Huang, Xiaojing Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Beijing 102206 China

In order to analyze the impact of variations of key parameters, such as load model and fault time etc., on power system dynamic stability, this paper applies a new method-the stochastic response surface method (SRSM) to analyze uncertainties of these parameters. Polynomial expressions between parameters and responses of system can be established by this method. Compared with the traditional approaches, the presented method can obtain statistical information with less simulation time. The case study on the IEEE 9-bus system demonstrates the validity of SRSM. Simulation results on the IEEE 39-bus system show that the uncertainties from key parameters, especially the different load model structures, have great impact on power system dynamic stability, which is directly related to the security and stability of power systems.

关键词： Monte Carlo methods

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Phase-selector based on voltage modal fault component

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Dianli Xitong Zidonghua/Automation of Electric power systems 2008年第9期32卷 42-46+99页

作者： Wang, Xingguo Huang, Shaofeng Liu, Qiankuan Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Beijing 102206 China

The characteristics of voltage modal transformation based on fault component in fault location and protection location are discussed in detail with regard to the changes of the system parameters and fault types. A new phase-selector based on voltage modal fault component is proposed. It uses voltage fault component and works fast after a fault occurs. A fault selection scheme is also proposed to solve problems of sensitivity as faults located on remote end of transmission lines. The simulation results of ATP and MATLAB show the feasibility of the scheme.

关键词： Electric power systems

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The Influence and Countermeasure to Transformer Differential protection of CT Saturation Caused by Ezternal Fault Removal

The Influence and Countermeasure to Transformer Differential...

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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： Jun Gu Tao Zheng Shaofeng Huang Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control (North China E Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control (North China E

The mal-operation of transformer differential protection will occasionally take place after the removal of external fault due to current-transformer (CT) saturation. Study show that CT saturation can be divided into three kinds. Firstly, the influencing factors of CT saturation and effect of CT saturation to transformer differential protection are studied. Secondly, this paper analyzes the characteristic of the operating point when differential protection is mal-operated because of CT saturation. At last a method of different time delay in different areas is presented to prevent the differential protection from maloperation. Simulation results validate its feasibility and reliability. It is significant if the method is realized for transformer protection.

关键词： Circuit faults Fault currents Current transformers Surge protection power system protection power system transients Hysteresis Magnetization processes Magnetic flux Saturation magnetization

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