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Time-domain Simulations (time-domain + simulation)

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Engineering100%

Selected Abstracts

A three-dimensional mesh refinement algorithm with low boundary reflections for the finite-difference time-domain simulation of metallic structures

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2010
W. H. P. Pernice
Abstract We present a method for including areas of high grid density into a general grid for the finite-difference time-domain method in three dimensions. Reflections occurring at the boundaries separating domains of different grid size are reduced significantly by introducing appropriate interpolation methods for missing boundary points. Several levels of refinement can be included into one calculation using a hierarchical refinement architecture. The algorithm is implemented with an auxiliary differential equation technique that allows for the simulation of metallic structures. We illustrate the performance of the algorithm through the simulation of metal nano-particles included in a coarser grid and by investigating gold optical antennas. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Computation of time delay margin for power system small-signal stability

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 7 2009
Saffet AyasunArticle first published online: 19 JUN 200
Abstract With the extensive use of phasor measurement units (PMU) in the wide-area measurement/monitoring systems (WAMS), time delays have become unavoidable in power systems. This paper presents a direct and exact method to compute the delay margin of power systems with single and commensurate time delays. The delay margin is the maximum amount of time delay that the system can tolerate before it becomes unstable for a given operating point. First, without using any approximation or substitution, the transcendental characteristic equation is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. The resulting polynomial also enables us to easily determine the delay dependency of the system stability and the sensitivities of crossing roots with respect to time delay. Then, an expression in terms of system parameters and imaginary root of the characteristic equation is derived for computing the delay margin. The proposed method is applied to a single-machine-infinite bus (SMIB) power system with an exciter. Delay margins are computed for a wide range of system parameters including generator mechanical power, damping and transient reactance, exciter gain, and transmission line reactance. The results indicate that the delay margin decreases as the mechanical power, exciter gain and line reactance increase while it increases with increasing generator transient reactance Additionally, the relationship between the delay margin and generator damping is found be relatively complex. Finally, the theoretical delay margin results are validated using the time-domain simulations of Matlab. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Learning to recognize vulnerable patterns due to undesirable Zone-3 relay operations

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2009
Koji Yamashita Member
Abstract Undesirable zone 3 relay operations caused by unexpected loading conditions can contribute to the cascaded events, leading to catastrophic outages. Identifying the basic patterns of zone 3 relay operations in advance is an effective way to help prevent cascaded events. The postcontingency impedances seen by zone 3 relays can be calculated on line in a steady state security assessment framework. However, their accuracy is inadequate compared with the postcontingency apparent impedance obtained from off-line time domain dynamic simulations. This paper proposes a fuzzy inference system (FIS) to correct discrepancies between the postcontingency apparent impedances obtained from the results of steady state security assessment and the corresponding values obtained by time-domain simulations. The postcontingency apparent impedances obtained from the results of steady state security assessment can be corrected on line using correction terms provided by the FIS. The dynamic model of a 200-bus system is used to validate the performance of the proposed FIS. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

Interference evaluations and simulations for multisatellite multibeam systems

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 4 2002
Pierpaolo Loreti
Third generation communication systems will be characterized by full integration between terrestrial and satellite components. To this aim, global coverage along with not severe requirements for user terminals are mandatory for the satellite segment and the use of constellations of satellites in low or medium Earth orbits (LEO or MEO) seems to be a viable solution. Those satellite systems will adopt multibeam antennas to achieve high spectral efficiency and low-cost terminals. Thus, interference becomes one of the most limiting factors in terms of both link availability and capacity. The paper presents a more complete interference model than previously published in literature. The identification of the interfering users set has been introduced and all the factors impacting interference generation or isolation have been considered in case of both FDMA and CDMA access. This model is suitable for instantaneous analysis of multisatellite constellations. It has been implemented and time-domain simulations have been performed to evaluate the impairments due to co-channel interference for different access techniques for LEO configuration. Simulation results on interference and users spatial distribution, on trade-offs between interference and system capacity will be presented. Finally, the main interference mitigation techniques will be listed and discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source]