Conductance Matrix Research Articles

Improved Complex Torque Coefficient Method Using CPCM for Multi-Machine System SSR Analysis

Calculation of the complex torque coefficient for multi-machine system subsynchronous resonance (SSR) assessment had been proven a hard task. In this paper the concept of complex frequency domain port-equivalence conductance matrix (CPCM) is introduced to model the individual system component which represents the relationship between the terminal voltage and current in frequency domain, and the model of the overall power system can be established easily. Thus the complex torque coefficients of the generator unit under investigation can be calculated for SSR assessment. The advantages of this proposed method are that it can take the shaft dynamics and the rotor angle interactions among the generator units into consideration for the multi-machine power system SSR analysis, as well as it can be used to analyze the effectiveness of SSR damping devices. The effectiveness of the proposed method has been verified by both the eigenvalue analysis and the time domain simulation.

Image reconstruction using voltage–current system in electrical impedance tomography

Electrical impedance tomography (EIT) has been used as an alternative imaging modality to visualize binary mixture like two-phase flows because of its high temporal resolution for monitoring fast transient processes. In this paper, voltage applied and current measured (VC) system based on complete electrode model is applied to image binary mixtures. The forward problem is formulated with the conductance matrix and a non-iterative inverse method is used to estimate the conductivity distribution. The proposed method with VC system needs simpler hardware as compared to conventional current applied and voltage measured system. Both numerical simulations and phantom experiments have been carried out to evaluate the performance of the proposed method through quantitative parameters. Results show a promising performance of VC system as an imaging modality for binary mixtures.

Fixator–Norator Pairs Versus Direct Analytical Tools in Performing Analog Circuit Designs

4and compared. They are used for partial designs with certain given 5 design criteria. The first approach, which is called direct analyti6 cal, works through the circuit conductance matrix, and it needs 7 linearity to perform. The second approach uses fixator–norator 8 pairs (FNPs), changing an analysis into a design problem. The 9 two methods are shown to be theoretically identical, except that 10 they use different tools to get the results. The advantage of using 11 FNP over the direct analytical method is that it can simply handle 12 nonlinearities, as it is done in a circuit analysis or simulation. The 13 drawback, however, is the lack of fixator and norator components 14 in a typical simulator; although, the closest components replacing 15 them can be the controlled sources with very high gains. 16 Index Terms—Amplifiers, analog circuit design, analytical 17 method, biasing design, circuit linearization, fixator–norator pairs 18 (FNPs). 19

A Phase-Domain Synchronous Machine Model With Constant Equivalent Conductance Matrix for EMTP-Type Solution

Interfacing machine models in either nodal analysis-based (EMTP-like) or state variable-based transient simulation programs play an important role in numerical accuracy and computational performance of the overall simulation. As an advantageous alternative to the traditional <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">qd</i> models, a number of advanced phase-domain (PD) and voltage-behind-reactance machine models have been recently introduced. However, the rotor-position-dependent conductance matrix in the machine-network interface complicates the use of such models in EMTP. This paper focuses on achieving constant and efficient interfacing circuit for the PD synchronous machine model. It is shown that the machine conductance matrix can be formulated into a constant submatrix plus a time-variant submatrix. Eliminating numerical saliency from the second term results in a constant conductance matrix of the proposed PD model, which is a very desirable property for the EMTP solution since the refactorization of the network conductance matrix at every time step is avoided. Case studies demonstrate that the proposed PD model represents a significant improvement over other established models used in EMTP while preserving the accuracy of the original/classical PD model.

Error bounds for reduction of multi-port resistor networks

The interconnect layouts of chips can be modeled by large resistor networks. In order to be able to speed up simulations of such large networks, reduction techniques are applied to reduce the size of the networks. For some class of networks, an existing reduction strategy does not provide sufficient reduction in terms of the number of resistors appearing in the final network. In this paper, we propose an approach for obtaining a further reduction in the amount of resistors. The suggested approach improves sparsity of the conductance matrix by neglecting resistors that do not contribute significantly to the behavior of the circuit. Explicit error bounds, which give an opportunity to control the errors due to approximation, have been derived. Numerical examples show that the suggested approach appears promising for multi-terminal resistor networks, and in combination with the existing reduction strategy, leads to better reduction. Copyright © 2013 John Wiley & Sons, Ltd.

A Mortar Cell Method for Electro-Thermal Contact Problems

A 3-D mortar domain decomposition approach based on the cell method (CM) for analyzing electro-thermal contact problems is presented. The computational domain is subdivided into non-overlapping regions discretized according to the CM, where variables and field equations are expressed directly in integral form suitable for coupling the contact problem to the electro-thermal one in the bulk regions. Voltage and temperature discontinuities at contact interfaces are modeled by diagonal conductance matrices. The electrical and thermal continuity between contacting regions is enforced by means of dual Lagrange multipliers. Nonlinear equations are cast into a saddle-point form ensuring existence and uniqueness of the solution. Problem size is reduced by the Schur complement approach. A 3-D finite-element software for multiphysics problems is used to validate the mortar cell method.

Superconducting-insulator transition in disordered Josephson junctions networks

The superconducting-insulator transition is simulated in disordered networks of Josephson junctions with thermally activated Arrhenius-like resistive shunt. By solving the conductance matrix of the network, the transition is reproduced in different experimental conditions by tuning thickness, charge density and disorder degree. In particular, on increasing fluctuations of the parameters entering the Josephson coupling and the Coulomb energy of the junctions, the transition occurs for decreasing values of the critical temperature T c and increasing values of the activation temperature T o . The results of the simulation compare well with recent experiments where the mesoscopic fluctuations of the phase have been suggested as the mechanism underlying the phenomenon of emergent granularityin otherwise homogeneous films. The proposed approach is compared with the results obtained on TiN films and nanopatterned arrays of weak-links, where the superconductor-insulator transition is directly stimulated.

Transport in a three-terminal graphene quantum dot in the multi-level regime

We investigate transport in a three-terminal graphene quantum dot. All nine elements of the conductance matrix have been independently measured. In the Coulomb blockade regime, accurate measurements of individual conductance resonances reveal slightly different resonance energies depending on which pair of leads is used for probing. Rapid changes in the tunneling coupling between the leads and the dot due to localized states in the constrictions have been excluded by tuning the difference in resonance energies using in-plane gates which couple preferentially to individual constrictions. The interpretation of the different resonance energies is then based on the presence of a number of levels in the dot with an energy spacing of the order of the measurement temperature. In this multi-level transport regime, the three-terminal device offers the opportunity to sense if the individual levels couple with different strengths to the different leads. This in turn gives qualitative insight into the spatial profile of the corresponding quantum dot wave functions.

Time-dependent theory of nonlinear response and current fluctuations

A general nonlinear response theory is derived for an arbitrary time-dependent Hamiltonian, not necessarily obeying time-reversal symmetry. We consider the application of this theory to a multiterminal mesoscopic system with arbitrary interactions and time-dependent voltages. This allows us to obtain a generalized Kubo-type formula. We derive a microscopic expression for the finite frequency differential conductance matrix, which preserves current conservation and gauge invariance. We exploit this result to show that the asymmetric part of the current fluctuation matrix at finite frequency obeys a generalized time-dependent fluctuation-dissipation theorem. In the stationary regime, this theorem provides a common explanation for the asymmetry of the excess noise with respect to positive and negative frequencies that has been obtained in several systems as a consequence of nonlinearity. It also explains the origin of the unexpected negative sign of the excess noise. Finally, we apply these general results to the case of a tunnel junction and obtain a nonperturbative out-of-equilibrium link between conductance and current fluctuations. We also derive a universal property of the finite frequency noise in the perturbative regime.

Spin-polarized transport in zigzag graphene nanoribbons with Rashba spin–orbit interaction

We have calculated spin-dependent conductance in zigzag graphene nanoribbons, attached to two leads, in the presence of Rashba spin−orbit interaction, based on the green function method. A tight binding model including Rashba spin-orbit interaction is used. It is shown that elements of conductance matrix crucially depend on the width and the length of the graphene nanoribbon for strong Rashba spin−orbit interaction.

Artificial Neural Networks Applied for Simultaneous Analysis of Mixtures of Nitrophenols by Conductometric Acid–Base Titration

In this study, the simultaneous conductometric titration method for determination of mixtures of 4-nitrophenol, 2,4-dinitrophenol, and 2,4,6- trinitrophenol based on principal component artificial neural network (ANN) calibration model was proposed. The three-layered feed-forward ANN trained by back-propagation learning was used to model the complex nonlinear relationship between the concentration of 4-nitrophenol, 2,4-dinitrophenol, and 2,4,6-trinitrophenol in their ternary mixtures and the conductance of the solutions at different volumes of titrant. The principal components of the conductance matrix were used as the input of the network. The network architecture and parameters were optimized to give low prediction error. The optimized networks predicted the concentrations of nitrophenols in synthetic mixtures. The results showed that the used ANN can proceed the titration data with low relative prediction errors (5.53%, 4.03%, and 4.71% for 4-nitrophenol, 2,4-dinitrophenol, and 2,4,6-trinitrophenol, re...

Non-iterative nodal solution for transient simulation of nonlinear and time-varying elements

A non-iterative algorithm based on nodal equation formulation is proposed for transient simulation of nonlinear and time-varying elements. Terminal equations of inductors and capacitors are transformed into algebraic equations using the trapezoidal rule of integration by treating all nonlinear elements as linear and nodal equations are formulated as a set of algebraic equations. LU factorization is used for the solution of nodal equations. Variation of system elements is represented by renewing the nodal conductance matrix at each time step of the solution accordingly. In the first illustrative example, a nonlinear oscillator circuit is considered. In the second, the transient response of a transmission line with a surge arrester is computed by including the corona effects and in the third, a time-dependent primary arc model of a faulty transmission line is examined. Obtained results are compared with those obtained using EMTP and state-space method. Change of simulation time with respect to the step length of the numerical integration is also investigated.

Constraints on conductances for Y-junctions of quantum wires

We consider the Y-junction, connecting three quantum wires, in the scattering states formalism. In the absence of fermionic interaction we analyze the restrictions on the values of conductance matrix, imposed by the unitarity of scattering S-matrix. Using the combination of numerical and analytical results, we describe the four-dimensional body of values of reduced conductance matrix. We show that this body touches the unit sphere at six points only, in accordance with Birkhoff-von Neumann theorem. It implies that the Abelian bosonization analysis for the vanishing interaction strength can be performed only in the vicinity of these six points.

Closed form Delay Model for on-Chip VLSIRLCG Interconnects for Ramp Input for Different Damping Conditions

Fast delay estimation methods, as opposed to simulation techniques, are needed for incremental performance driven layout synthesis. On-chip inductive effects are becoming predominant in deep submicron interconnects due to increasing clock speed and circuit complexity. Inductance causes noise in signal waveforms, which can adversely affect the performance of the circuit and signal integrity. Several approaches have been put forward which consider the inductance for on-chip interconnect modelling. But for even much higher frequency, of the order of few GHz, the shunt dielectric lossy component has become comparable to that of other electrical parameters for high speed VLSI design. In order to cope up with this effect, on-chip interconnect has to be modelled as distributed RLCG line. Elmore delay based methods, although efficient, cannot accurately estimate the delay for RLCG interconnect line. In this paper, an accurate analytical delay model has been derived, based on first and second moments of RLCG interconnection lines. The proposed model considers both the effect of inductance and conductance matrices. We have performed the simulation in 0.18μm technology node and an error of as low as less as 5% has been achieved with the proposed model when compared to SPICE. The importance of the conductance matrices in interconnect modelling has also been discussed and it is shown that if G is neglected for interconnect line modelling, then it will result an delay error of as high as 6% when compared to SPICE.

Voltage–current characteristics of multiterminal HVDC-VSC for offshore wind farms

AbstractVoltage–current characteristics and equilibrium points for the DC voltages of multiterminal HVDC systems using voltage source converters are discussed. The wind farm rectifiers and grid connected inverters are analyzed through their operating modes, governing equations and graphical characteristics. Using the converter equations and the HVDC grid conductance matrix the equilibrium voltages and currents are found. Case studies are presented considering wind power generation, loss of a converter and voltage sags in the AC grid.

A geospatial modelling approach integrating archaeobotany and genetics to trace the origin and dispersal of domesticated plants.

BackgroundThe study of the prehistoric origins and dispersal routes of domesticated plants is often based on the analysis of either archaeobotanical or genetic data. As more data become available, spatially explicit models of crop dispersal can be used to combine different types of evidence.Methodology/Principal FindingsWe present a model in which a crop disperses through a landscape that is represented by a conductance matrix. From this matrix, we derive least-cost distances from the geographical origin of the crop and use these to predict the age of archaeological crop remains and the heterozygosity of crop populations. We use measures of the overlap and divergence of dispersal trajectories to predict genetic similarity between crop populations. The conductance matrix is constructed from environmental variables using a number of parameters. Model parameters are determined with multiple-criteria optimization, simultaneously fitting the archaeobotanical and genetic data. The consilience reached by the model is the extent to which it converges around solutions optimal for both archaeobotanical and genetic data. We apply the modelling approach to the dispersal of maize in the Americas.Conclusions/SignificanceThe approach makes possible the integrative inference of crop dispersal processes, while controlling model complexity and computational requirements.

Approximate Voltage-Behind-Reactance Induction Machine Model for Efficient Interface With EMTP Network Solution

A so-called voltage-behind-reactance (VBR) induction machine model has recently been proposed for the Electro-Magnetic Transient Program (EMTP) solution as an advantageous alternative to the traditional qd and phase-domain (PD) models. This paper focuses on achieving an efficient interface of the machine models with the EMTP network. It is shown first that a discretized PD model can be formulated to have a constant machine conductance submatrix, which is a very desirable numerical property that allows avoiding the re-factorization of the network conductance matrix at every time step. Furthermore, an approximate voltage-behind-reactance (AVBR) model is proposed where the rotor-speed-dependent coefficients are neglected, thus leading to a similar constant machine conductance submatrix and efficient interface. Case studies demonstrate that the new AVBR model represents a significant improvement in terms of numerical accuracy and efficiency over other established models used in EMTP.

Causality Preserving Passivity Enforcement for Traveling-Wave-Type Transmission-Line Models

Transmission-line models must be passive in order to guarantee stable time-domain simulations. Enforcing the passivity by adding a conductance matrix to the line model has been proposed, which is established by a frequency sweep. This leads to instantaneous coupling between the two line ends, thus violating the causality of the line. This letter shows that the coupling terms can be removed with only a negligible change to the model's perturbation. The removal of coupling terms makes the approach more suitable for the application with existing transmission-line models.

Coupling geological and numerical models to simulate groundwater flow and contaminant transport in fractured media

A new modeling approach is presented to improve numerical simulations of groundwater flow and contaminant transport in fractured geological media. The approach couples geological and numerical models through an intermediate mesh generation phase. As a first step, a platform for 3D geological modeling is used to represent fractures as 2D surfaces with arbitrary shape and orientation in 3D space. The advantage of the geological modeling platform is that 2D triangulated fracture surfaces are modeled and visualized before building a 3D mesh. The triangulated fractures are then transferred to the mesh generation software that discretizes the 3D simulation domain with tetrahedral elements. The 2D triangular fracture elements do not cut through the 3D tetrahedral elements, but they rather form interfaces with them. The tetrahedral mesh is then used for 3D groundwater flow and contaminant transport simulations in discretely fractured porous media. The resulting mesh for the 2D fractures and 3D rock matrix is checked to ensure that there are no negative transmissibilities in the discretized flow and transport equation, to avoid unrealistic results. To test the validity of the approach, flow and transport simulations for a tetrahedral mesh are compared to simulations using a block-based mesh and with results of an analytical solution. The fluid conductance matrix for the tetrahedral mesh is also analyzed and compared with known matrix values.

A Half-Size Singularity Test Matrix for Fast and Reliable Passivity Assessment of Rational Models

One major difficulty in the rational modeling of linear systems is that the obtained model can be nonpassive, thereby leading to unstable simulations. The model's passivity properties are usually assessed by computing the eigenvalues of a Hamiltonian matrix, which is derived from the model parameters. The purely imaginary eigenvalues represent crossover frequencies where the model's conductance matrix is singular, allowing to pinpoint frequency intervals of passivity violations. Unfortunately, the eigenvalue computation time can be excessive for large models. Also, the test applies only to symmetrical models, and the testing is made difficult by numerical noise in the extracted eigenvalues. In this paper a new (non-Hamiltonian) half-size singularity test matrix is derived for use with admittance parameter state-space models, which overcomes these shortcomings. It gives a computational speedup by a factor of eight; it is applicable to both symmetric and unsymmetrical models; and it produces noiseless eigenvalues for reliable passivity assessment.