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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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New algorithm to distinguish the transferring fault of transformer protection based on morphological gradient

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Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering 2008年第22期28卷 75-80页

作者： Zheng, Tao Gu, Jun Huang, Shao-Feng Wang, Zeng-Ping Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Beijing 102206 China

Distinguishing the transferring fault is one of difficulties for transformer differential protection. According to CT (current transformer) saturation characteristic, a new algorithm of distinguishing the transferring fault is put forward. As the primary current of CT crosses zero, a small linear transmission part of CT would appear, no matter how CT saturated. Based on this characteristic, the waveform of the differential current would expose discontinuous parts when an external fault occurred;in contrast, this phenomenon would not appear for an internal fault. The morphological gradient is adopted to deal with the waveform between two adjacent extremal points of the differential current. By dividing the gradient waveform into three parts and calculating each part's area, the discontinuous in the differential current could be detected according to the relative size of three above areas. By judging whether the discontinuous parts are existed in the differential current, the transferring faults could be easily distinguished. Simulation results show that this algorithm can distinguish the internal fault, external fault and the fault transferred from the external to the internal under the condition of CT saturation.

关键词： Electric instrument transformers

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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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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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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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SPWM type static var compensator with continuously bi-directional reactive power control capability

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Dianli Xitong Zidonghua/Automation of Electric power systems 2008年第15期32卷 75-78页

作者： Shan, Renzhong Yin, Zhongdong Xiao, Xiangning Song, Qipeng Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Beijing 102206 China

This paper proposes a novel static VAR compensator, which can regulate capacitor and inductor continuously. The proposed compensator uses the SPWM type inverter to regulate the voltage on the compensating capacitors and inductors directly, therefore can continuously control the compensator bi-directional outputs. It is very useful in the low and medium voltage distribution system. The compensator overcomes harmonics problem associated with the conventional thyristor controlled reactor (TCR), and the capacity of the inverter is only 25% of its compensation capacity. The main circuit consists of three-phase four-leg inverters, which can efficiently compensate unbalanced reactive loads. Experimental results validate the compensator feasibility and efficiency.

关键词： Static Var compensators

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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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Immune genetic algorithm based on regulating new definition of antibody density for power system reactive power optimization

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Diangong Jishu Xuebao/Transactions of China Electrotechnical Society 2008年第2期23卷 115-119页

作者： Li, Yulong Zong, Wei Lu, Xianyan He, Qiuyu Yuan, Qihong Wang, Qian Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control North China Electric Power University Beijing 102206 China

By integrating an immune genetic algorithm, a regulating strategy based on a new definition of antibody density for reactive power optimization in power system is proposed. Firstly, the penalty coefficient adjusted dynamically was applied to the objective function. Then artificial immunity mechanism is introduced into the genetic operation. It is similar to consider to be each antibody on encoding. And then based on similar vector distance choice tactics were proposed, which keep the population diversity. At the same time, it can guarantee algorithms faster convergence. Thus simple genetic algorithm was correspondingly improved. Finally, the proposed method is applied to IEEE30 buses test systems. The result of calculation illustrates that the proposed hybrid strategy is effective. It shows that compared with SGA in the same condition, this approach can reduce remarkably iterative times and improve rate of convergence of the algorithm for reactive power optimization.

关键词： Genetic algorithms

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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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Study on assessment method of load's disturbance property

Study on assessment method of load's disturbance property

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3rd International Conference on Deregulation and Restructuring and power Technologies, DRPT 2008

作者： Jia, Xiufang Bo, Zhang Fazhan, Liu Minghao, Sun Key Laboratory of Power System Protection and Dynamic Security Monitoring and Control Ministry of Education North China Electric Power University Baoding 071003 Hebei Province China Zhengzhou Power Supply Company Zhengzhou 450012 Henan Province China

ISBN: (纸本)9787900714138

Assessment of load's disturbing property needs to be studied for confirming power quality responsibility and making a power price by its quality. In this paper, load's disturbing property is assessed by means of the analytic hierarchy process (AHP) and the grey relational analysis (GRA). First, the weight of index such as power factor, current total harmonic distortion, unbalance factor and reactive power fluctuation, which can characterize load's property, is obtained by AHP method. In order to assess the degree of load disturbance, a standard load in power system is defined. Then, based on the GRA, can get relativity degree between each disturbing load and standard load. Relativity degree can describe the gap between each disturbing load and standard load. The degree that disturbing loads creates influence to the electrical network is known by means of relativity degree. Finally, Calculating examples are brought forth to validate feasibility of the method. © 2008 DRPT.

关键词： Analytic hierarchy process

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