20,574 research outputs found
Practical considerations regarding power factor for nonlinear loads
This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of Brunel University's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. Copyright @ 2004 IEEEThe choice of LC compensator may be constrained by the availability of manufacturers units. To account for this, the capacitor values are chosen from among standard values and for each value the transmission losses is minimized, or power factor is maximized, or transmission efficiency is maximized. The global minimum or maximum is obtained by scanning all local minims or maxims. The performance of the obtained compensator is discussed by means of numerical examples
A mathematical model and inversion procedure for Magneto-Acousto-Electric Tomography (MAET)
Magneto-Acousto-Electric Tomography (MAET), also known as the Lorentz force
or Hall effect tomography, is a novel hybrid modality designed to be a
high-resolution alternative to the unstable Electrical Impedance Tomography. In
the present paper we analyze existing mathematical models of this method, and
propose a general procedure for solving the inverse problem associated with
MAET. It consists in applying to the data one of the algorithms of
Thermo-Acoustic tomography, followed by solving the Neumann problem for the
Laplace equation and the Poisson equation.
For the particular case when the region of interest is a cube, we present an
explicit series solution resulting in a fast reconstruction algorithm. As we
show, both analytically and numerically, MAET is a stable technique yilelding
high-resolution images even in the presence of significant noise in the data
Comparison of different optimization criteria for optimal sizing of hybrid active power filters parameters
Praise Worthy Prize granted a permission for Brunel University London to archive this article in BURA.Harmonic distortion in power systems has increased considerably due to the increasing use of nonlinear loads in industrial firms and elsewhere. This distortion can give rise to overheating in all sectors of the power system, leading to reduced efficiency, reliability, operational life and sometimes failure. This article seeks to propose a new methodology for the optimal sizing of hybrid active power filter (HPF) parameters in order to overcome the difficulties in hybrid power filters design when estimating the preliminary feasible values of the parameters. Sequential Quadratic Programming based on FORTRAN subroutines is used to find out the planned filter size in two different optimization criteria depending on design concerns. The first criterion is to minimize the total voltage harmonic distortion. The second one is to maximize the load power factor, while taking into account compliance with IEEE standard 519-1992 limits for the total voltage harmonic distortion and the power factor.The effectiveness of the proposed filter is discussed using four exemplary case
Determining Geological Properties by a Hybrid Seismic-Magnetotelluric Approach
This paper concerns the controlled source audio magnetotelluric technique (CSAMT) for imaging subsurface structure. Given the short time available, we limited our investigation to a simple 1D earth model where regional seismic and well logs suggest discrete layers, each with constant seismic velocity and constant electrical conductivity. In addition, the well logs provide rough estimates of velocity and conductivity for use as a starting point in the seismic and MT inversions
A mathematical and numerical framework for ultrasonically-induced Lorentz force electrical impedance tomography
We provide a mathematical analysis and a numerical framework for Lorentz
force electrical conductivity imaging. Ultrasonic vibration of a tissue in the
presence of a static magnetic field induces an electrical current by the
Lorentz force. This current can be detected by electrodes placed around the
tissue; it is proportional to the velocity of the ultrasonic pulse, but depends
nonlinearly on the conductivity distribution. The imaging problem is to
reconstruct the conductivity distribution from measurements of the induced
current. To solve this nonlinear inverse problem, we first make use of a
virtual potential to relate explicitly the current measurements to the
conductivity distribution and the velocity of the ultrasonic pulse. Then, by
applying a Wiener filter to the measured data, we reduce the problem to imaging
the conductivity from an internal electric current density. We first introduce
an optimal control method for solving such a problem. A new direct
reconstruction scheme involving a partial differential equation is then
proposed based on viscosity-type regularization to a transport equation
satisfied by the current density field. We prove that solving such an equation
yields the true conductivity distribution as the regularization parameter
approaches zero. We also test both schemes numerically in the presence of
measurement noise, quantify their stability and resolution, and compare their
performance
High-performance Parallel Solver for Integral Equations of Electromagnetics Based on Galerkin Method
A new parallel solver for the volumetric integral equations (IE) of
electrodynamics is presented. The solver is based on the Galerkin method which
ensures the convergent numerical solution. The main features include: (i) the
memory usage is 8 times lower, compared to analogous IE based algorithms,
without additional restriction on the background media; (ii) accurate and
stable method to compute matrix coefficients corresponding to the IE; (iii)
high degree of parallelism. The solver's computational efficiency is shown on a
problem of magnetotelluric sounding of the high conductivity contrast media. A
good agreement with the results obtained with the second order finite element
method is demonstrated. Due to effective approach to parallelization and
distributed data storage the program exhibits perfect scalability on different
hardware platforms.Comment: The main results of this paper were presented at IAMG 2015 conference
Frieberg, Germany. 28 pages, 11 figure
Conductivity imaging from one interior measurement in the presence of perfectly conducting and insulating inclusions
We consider the problem of recovering an isotropic conductivity outside some
perfectly conducting or insulating inclusions from the interior measurement of
the magnitude of one current density field . We prove that the
conductivity outside the inclusions, and the shape and position of the
perfectly conducting and insulating inclusions are uniquely determined (except
in an exceptional case) by the magnitude of the current generated by imposing a
given boundary voltage. We have found an extension of the notion of
admissibility to the case of possible presence of perfectly conducting and
insulating inclusions. This also makes it possible to extend the results on
uniqueness of the minimizers of the least gradient problem
with to cases where
has flat regions (is constant on open sets)
On the Generation of Large Passive Macromodels for Complex Interconnect Structures
This paper addresses some issues related to the passivity of interconnect macromodels computed from measured or simulated port responses. The generation of such macromodels is usually performed via suitable least squares fitting algorithms. When the number of ports and the dynamic order of the macromodel is large, the inclusion of passivity constraints in the fitting process is cumbersome and results in excessive computational and storage requirements. Therefore, we consider in this work a post-processing approach for passivity enforcement, aimed at the detection and compensation of passivity violations without compromising the model accuracy. Two complementary issues are addressed. First, we consider the enforcement of asymptotic passivity at high frequencies based on the perturbation of the direct coupling term in the transfer matrix. We show how potential problems may arise when off-band poles are present in the model. Second, the enforcement of uniform passivity throughout the entire frequency axis is performed via an iterative perturbation scheme on the purely imaginary eigenvalues of associated Hamiltonian matrices. A special formulation of this spectral perturbation using possibly large but sparse matrices allows the passivity compensation to be performed at a cost which scales only linearly with the order of the system. This formulation involves a restarted Arnoldi iteration combined with a complex frequency hopping algorithm for the selective computation of the imaginary eigenvalues to be perturbed. Some examples of interconnect models are used to illustrate the performance of the proposed technique
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