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In order to solve mode mixing, an improved HHT (IHHT) is proposed to identify modes of low frequency oscillation (LFO) in power systems. Firstly, by means of Fourier transform the approximate frequency range of every mode is determined; then methods such as masking signals or filters are chosen to separate mixing modes. Finally mode parameters can be calculated by linear least quadratic fitting. Simulated...
Dynamic simulation of a metropolitan power grid shows that the dynamic load model has a significant impact on the rms value of symmetrical component of short-circuit current within 50 ms after fault which is conform to the corresponding result extracted from the fault-recording data of a real power grid fault accident . The simulation and the fault recording data both indicate that the result from...
With the introduction of new guidelines regarding the connection of large wind farms to the grid, wind farms and equipment providers are facing with new opportunities and challenges. One of which is low voltage ride-through (LVRT). Despite of the new installations, there are a considerable number of wind turbines to be reformed to meet the requirements. In this paper, a brief explanation of the principle...
Recently wind energy has developed at a fast pace, and it is necessary to develop equivalent models to represent dynamic behaviors of wind farms on power system. This paper investigates the applications of the equivalent wind method for the aggregation of DFIG wind turbines. Simulations in a practical power system have been used to verify the effectiveness of the aggregation.
This paper presents an on-line equivalent algorithm for power system based on phasor measurement unit. The method considers the changes of the system parameters and load level, which overcome parameters rift problem and the shortage of traditional two points power flow method that supposing the parameters are fixed after a small disturbance. On this basis, voltage stability and Alert margin are proposed,...
Load model has great uncertainty characteristic due to the time-variation of load. As a consequent, it is essential to analyze the influence of load model on power system stability. The effect of load model structure and parameter on Yunnan power grid transient stability is researched in this paper. Simulation results indicate that load model has great influence on Yunnan power great transient stability...
An accurate model of large scale wind farm is demanded for researches about the impacts on the power grid. The total number of wind energy generators is so large that the detailed model of wind farm is computationally prohibitive. Dynamic equivalence can significantly reduce system order with the major characteristics retained. So the aggregation of large scale wind farm is inevitable. An overview...
To study the influence of hydraulic characteristics in the interface zone between the runner outlet and the draft tube inlet, a decomposition and calculation method of the effective head of hydro turbine is proposed in this paper. Firstly, it analyzes traditional definition and composition of the hydro turbine head, and proposes that inlet zone of the draft tube should be decomposed into few parts...
A dynamic equivalent approach based on coherency is researched for dynamic simulation test in ±800 kV DC transmission project from Yunnan to Guangdong in China. To reduce the full system, the dynamic equivalent model of large-scale power system based on coherency is established, in which the identification of coherent generator groups, coherent buses reduction, aggregation coherent generator parameters...
Voltage stability has become rather important in modern power systems, the bifurcation of the adjoint system has been proposed for computing the saddle-node bifurcation point of the voltage stability. We derive the bifurcation analysis of the adjoint system, an example is given.
A new heuristic optimization algorithm is proposed in the paper, that is an improved ant colony algorithm for solving continuous space optimization problems. It is used in dynamic parameter aggregation based on frequency domain aggregation. The result from aggregation of generator electromagnetic circuit and excitation system show that an improved ant colony algorithm in aggregation of generator dynamic...
This manuscript presents an analysis of the dynamic performance of a multimachine power system in the presence of device Flexible AC Transmission Systems (FACTS) acting in conjunction with robust controllers. Model Power Sensitivity (PSM) is used to represent the multimachine power system. The design of the controllers Power System Stabilizers (PSS) and Power Oscillation Damping (POD) is performed...
This paper presents a novel group multi-criteria decision-making method for power system skeleton restoration. The proposed method improves the technique for order preference by similarity to an ideal solution (TOPSIS) in supporting group decision-making. This method can comprehensively consider the safety margin and restoration rate of power system, and can be used to support the restoration decision-making...
To assist dispatchers to on-line monitor small signal stability of power grid, this paper proposed an artificial intelligent method-Case-Based Reasoning(CBR) theory to predict small signal stability based on measurement data of wide area measurement system (WAMS). Oscillatory active power increment distribution (OAPID) was introduced to improve the prediction accuracy. The designing process of small...
The paper discusses the characteristic of single phase fault in Petersen-coil-grounded distribution grid, analyzes the zero sequence voltage and currents of the Petersen-coil, fault point, fault feeder and sound feeders. Adaptive Petersen-coil is applied to help detecting and extinguishing the single earth fault. And the paper studies characteristic of the derivatives of the zero sequence currents...
Voltage stability problems caused by on-load Tap Changer (OLTC) action and load dynamic characteristics are more complicated and not easy to grasp. By means of the Pmax - Φ and Vcr - Φ curves, this paper analyses the influence of OLTC on the static voltage stability limit, and studies the critical variable ratio corresponding to the OLTC adjustment. The Pmax - Φ and Vcr - Φ curves gradually shift...
Abstracting the general concept of information and relative state of element, based on the structure and state research of complex network, this paper takes the branch potential energy as edge weight into the complex network modeling process of power system. It analyzes the physical meaning of element information and clarifies the physical meaning of the network parameters including steady energy...
Dynamic Security Assessment (DSA) is an important way for ensuring the secure and reliable operation of power systems. The current trend is to perform DSA on line using near real-time data. One of the modeling considerations for DSA is special protection systems (SPS). This paper describes a framework that is designed to model SPS for DSA, particularly with respect to on-line applications. It is based...
The idea of smart grid is currently receiving much attention. However, there are differences in understanding of concept of smart grid and in how this concept should be implemented. Moreover, there is no clear agreement, worldwide, on what a power grid must include in order to be considered as smart grid. The fact is that with a growing demand for reliable and sustainable power supply, there is a...
Aimed on solving the potential difficulty of power grid operation and dispatching in wind power developed provinces of china, this paper presents a modeling methodology of day-ahead optimal dispatching to coordinate wind power. By considering the short-term and medium-and-long-term wind power prediction, the day-ahead optimal dispatching decision process combined with the concept of energy saving...
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