Adaptability analysis of current diffrerential protection for linces of doubling-fed induction generator station connection to flexible-direct grid
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In the Zhangbei Flexible-DC Grid Demonstration Project, both ends of the connecting line between the remote new energy station and the flexible and direct power grid are systems containing power electronic devices, which have obvious weak feed characteristics and aperiodic components during faults, which brings new challenges to line protection. In this paper, the characteristics of the fault current of the Doubling-Fed Induction Generator (DFIG) sending line and the AC line of Modular Multilevel Converter(MMC) sending end are analyzed separately, combined with the protection principle of the current differential, the adaptability of the current differential is studied, and the conclusions are drawn: 1. When the short-circuit capacity on both sides of the line has a large difference and a serious fault occurs, the current differential protection can operate reliably; 2. When the short-circuit capacity on both sides of the line is similar, under a serious fault, due to the influence of the aperiodic component of DFIG, the current differential protection may not act; 3. The weak feed-in characteristics of the double-ended system will lead to a decrease in the sensitivity of the protection. At last, the system model is built, and the simulation results verify the conclusion of the theoretical analysis.Keywords:
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Abstract The origin and stability of quasicrystals are still heavily debated issues. One may ask the same questions about aperiodic crystals in general. For some other classes, there are answers to these questions, and it is useful to compare the situations. A short discussion is given of what is known for the various classes of aperiodic crystals.
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We study the periodicity of subshifts of finite type (SFT) on Baumslag-Solitar groups. We show that for residually finite Baumslag-Solitar groups there exist both strongly and weakly-but-not-strongly aperiodic SFTs. In particular, this shows that unlike $\mathbb{Z}^2$, but like $\mathbb{Z}^3$, strong and weak aperiodic SFTs are different classes of SFTs in residually finite BS groups. More precisely, we prove that a weakly aperiodic SFT on BS(m,n) due to Aubrun and Kari is, in fact, strongly aperiodic on BS(1,n); and weakly but not strongly aperiodic on any other BS(m,n). In addition, we exhibit an SFT which is weakly but not strongly aperiodic on BS(1,n); and we show that there exists a strongly aperiodic SFT on BS(n,n).
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Variable speed constant frequency doubly fed induction generator(VSCF-DFIG)is the main direction in development and appliance of wind turbine generator.The control technology plays significant role in large-scale wind power usage.Based on the analysis of the operating characteristics of VSCF doubly-fed induction generator,no-load grid-connection techniques and the excitation control strategies,especially the vector control methods,for the DFIG were generalized and analyzed by comparison.Finally,it summarizes the current research hotspots and forecasts the tendency in future.
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In this work we introduce a virtual laboratory, APERIODIC DIFFRACT, developed in Matlab GUI c (Graphical User Interface) as an informatics tool for teaching the diractive properties of aperiodic gratings. This GUI allows the student to generate aperiodic sequences by iterating and lets to study the spectra for dierent iterating orders.
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A novel grid connection strategy of double-fed induction generator(DFIG)wind generation system is proposed.Mathematical model of DFIG in synchronous coordinate system were made.Grid voltage oriented vector control strategy was implemented to control DFIG.Stagewise control strategy was proposed for connecting DFIG to the grid.Overall controllers were designed and implemented.The control strategy was implemented on a simulation platform of AC excited DFIG wind generation system.Experiment results verified the proposed control strategy.
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This thesis presents two types of alternating current (ac) generators that are becoming popular for use in small-scale distributed generation and in autonomous (or standalone) power systems. For the induction generator (IG), two modes of operation are identified, namely operation on the power grid and operation in the isolated mode. Single-phase operation is emphasized due to its applicability in remote rural regions where electrification is both costly and difficult to carry out. In the case of gridconnected operation, a number of practical phase-balancing schemes for a three-phase IG are proposed and analyzed. The method of symmetrical components is found to be a versatile tool for analyzing all the circuit configurations to be studied, including the Smith connection. Microcontroller-based multi-mode operation of an IG with the Smith connection is also investigated. When operated in the stand-alone mode, the IG is more commonly known as the selfexcited induction generator (SEIG). In this thesis, a unified approach that combines the method of symmetrical components and the pattern search method of Hooke and Jeeves is used to analyze a three-phase SEIG which supplies asymmetrical or single-phase loads. Its applicability is tested on various SEIG schemes, including the Steinmetz connection, modified Steinmetz connection (MSC), the simplified Steinmetz connection (SSC), the self-regulated self-excited induction generator (SRSEIG), and SEIG with the Smith connection (SMSEIG). For certain studies, the above approach is used in association with an iterative procedure in order to obtain the solution. A coupled circuit and field approach based on a two-dimensional finite element method (2-D FEM) is proposed for analyzing a grid-connected IG with the Steinmetz connection. The technique of coupling the single-phase circuit equations to the field domain equations is set forth and a rotor circuit model that accounts for the nonuniform current distribution in the rotor winding is also presented. A voltage and frequency control scheme that employs an SEIG with slip-ring rotor, namely the SESRIG, is also proposed and investigated. The feasibility of using an external rotor resistance as a control parameter is demonstrated theoretically and experimentally. The study on the permanent-magnet synchronous generator (PMSG) is focused on autonomous power system applications. A PMSG with inset rotor, which possesses an inverse saliency characteristic, is found to give satisfactory performance when supplying isolated loads. Zero voltage regulation and other extremum conditions are deduced based on the two-axis model. A saturated two-axis model that gives a more accurate prediction of the load characteristic is developed. For a more rigorous analysis, a coupled circuit and field, time-stepping 2-D FEM is also proposed.
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This paper analyzes the energizing procedure of the modular multilevel converter (MMC) HVDC connected offshore wind farm (OWF). By means of electromagnetic transient (EMT) simulations, inrush currents to OWF, HVDC and wind turbine transformers, charging currents to AC and DC cables are analyzed. Furthermore, optimal energizing methods for reducing the inrush and charging currents are also proposed. Simulation results verify the proposed methods.
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In order to evaluate the eco-economic adaptability of crops production,the concepts and calculative methods of ecological potential capacity and market potential capacity were put forward,the dynamic threshold value system of the indexes for the eco-economic adaptability of different crop-region combinations was established,the calculative method of the single ecoeconomic adaptability indexes,the comprehensive eco-economic adaptability indexes which reflects the principle of minimum factor and the apparent eco-economic adaptability indexes and the regional comprehensive apparent eco-economic adaptability indexes which reflects practical situation of crops production were built up.12 representative counties in Jiangsu Province were selected to analysis,and 77 combinations of eco-economic adaptability indexes,apparent eco-economic adaptability indexes of crop-region and 12 regional comprehensive apparent eco-economic adaptability indexes were obtained.By comparative analysis,the result could be used as guidance for preferential order of productive arragement of crops among different regions.The method could be used as eco-economic adaptability for different crop-region combinations.
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