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Detailed switching models of ac–dc converters are available in many offline and real-time electromagnetic transient (EMT) simulation programs. However, such discrete models typically require small simulation time steps for accurately handling the switching events without interpolation. This paper proposes a new parametric modeling approach for line-commutated and 2-level voltage-source ac–dc converters. The proposed methodology is based on parametric functions that relate ac and dc variables in the instantaneous sense, which allows the reconstruction of the waveforms of voltages and currents (with the same level of details as the switching models of converters) without topological changes in the converter circuit. Thus, it can operate at larger time steps without requiring interpolation, thereby enhancing simulation efficiency. The computational advantages of the proposed models over the conventional switching models are demonstrated in offline PSCAD and real-time RTDS NovaCor simulators in terms of maximum possible time step size and accuracy. It is shown that the proposed models can accurately run with much larger time steps (up to ∼200 μs for LCRs, and up to ∼50 μs for VSCs) compared to detailed switching models, which are limited to relatively small time steps of ∼10 μs.

Based on $\tau$ -value concept of cooperative game theory, this paper presents a technique for efficient loss allocation in radial and weakly meshed distribution network (DN). The application of $\tau$ -value concept requires the quasi-balanced condition to be satisfied by the game. Therefore, with suitable mathematical derivations, it is demonstrated that a DN having only load or only distributed generation (DG) satisfies the necessary quasi-balanced condition. Then, a two-step method to allocate the network losses among loads and DGs is presented. Further, the intensive computational burden involved in $\tau$ -value method limits its applicability to practical DN. Therefore, by suitable mathematical analysis, computational complexity associated with $\tau$ -value method is reduced. The proposed method is tested on a few possible scenarios of loading, DG penetration, DG location, and X/R ratio in radial and weakly meshed DNs. The results obtained by the proposed $\tau$ -value, conventional $\tau$ -value, Shapley value and branch current decomposition method are compared based on the attributes of fair and efficient loss allocation. [ABSTRACT FROM AUTHOR]

A hybrid higher order discontinuous Galerkin time-domain (DGTD) method and finite-element time-domain (FETD) method with parallel technique is proposed for electromagnetic (EM)–circuital–thermal co-simulation in this article. For electromagnetic simulation, DGTD method with higher order hierarchical vector basis functions is used to solve Maxwell equation. Circuit simulation is carried out by modified nodal analysis method. For thermal simulation, FETD method with higher order interpolation scalar basis functions is adopted to solve heat conduction equation. To implement electromagnetic–circuital–thermal co-simulation, the electromagnetic and circuital equations are strongly coupled through voltages, currents, and electric fields at the lumped ports first. Then the electromagnetic and thermal equations are weakly coupled with electromagnetic loss and temperature-dependent medium parameters. Finally, large-scale parallel technique is used to accelerate the process of multiphysics simulation. Numerical results are given to validate the correctness and capability of the proposed electromagnetic–circuital–thermal co-simulation method. [ABSTRACT FROM AUTHOR]

Construction of the linearized state-space model is the key step of eigenvalue analysis for SSO study of power systems with large-scale renewable power generation (RPG) integrated. This paper proposes a novel method to construct the state matrix of the AC/DC hybrid power system with RPG within the discrete-time domain. The continuous-time state-space model of each AC/DC component as well as RPG units in the power system, is discretized together with their corresponding control. The discretized equation of each component is then represented by an equivalent circuit consisting of parallel historical current and conductance. According to the power system configuration, the discrete-time equivalent circuit of the whole AC/DC hybrid system is established, and the nodal analysis method is applied for the construction of the discrete-time state-space model of the power system. In this way, the state matrix can be acquired much more conveniently than that of continuous-time state-space method, which needs topology analysis to find independent state variables of the network from the proper tree. The proposed method has been applied in the eigenvalue analysis for the SSO study of a case system adapted from the AC/DC hybrid transmission system in northwest China. Eigenvalue results are in high accordance with time-domain simulation results in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

In-memory computing (IMC) has the potential of accelerating data-intensive computing tasks, such as inference and training of neural networks, by the matrix vector multiplication (MVM) in the crosspoint array. As the array size increases, however, a significant problem arises due to the parasitic IR drop at row and column lines. Understanding and compensating IR drop is essential to enable high-density accelerators of MVM. This work presents an analytical model for the IR drop and a numerical algorithm capable of accelerating the nodal analysis of crosspoint arrays up to five orders of magnitude with respect to SPICE analysis. The numerical algorithm is used to study the impact of array size, data density, device/wire resistance, and nonlinearity on the IR drop and the related loss of accuracy in IMC. We also derive two simple compensation schemes and an architectural solution for the mitigation of IR drop that are able to increase the accuracy of neural networks from 59% up to 96.6%, compared to an ideal accuracy of 97%. [ABSTRACT FROM AUTHOR]

The modular multilevel matrix converter (M3C) is a promising topology for high-voltage and high-power direct ac-to-ac power conversion applications. Fault tolerance ability is one of the advantages of the M3C. To further enhance the reliability of the M3C, this article proposes a novel branch current configuration method for branch fault conditions, which is available either one or two branches are failed. By deriving basic branch current configurations and analyzing branch dc power equations under branch fault conditions, feasible branch current configurations can be directly derived. In terms of minimizing the maximum peak branch current, the derived configuration is also the optimal one for the single branch fault condition. Compared with the existing method, the proposed method does not need to solve configuration coefficients of branch currents offline, which is automatically adaptive to different load conditions. An M3C prototype with three submodules each branch is built, and experimental results are presented to validate the proposed branch fault tolerance method. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to dynamic phasor-based transient stability simulation. The proposed method is based on the modified nodal analysis (MNA) approach to circuit simulation, which is used to construct continuous differential-algebraic equations (DAEs). The proposed method makes use of the stamp technique, which makes it possible to construct a general purpose MNA-based simulator. Stamp-based models for common power system components are derived in this work. A new MNA-based synchronous machine model is presented, which represents machines as nonlinear inductances instead of subtransient equivalents. The resultant continuous DAEs are numerically solved using the general purpose variable step and variable order library IDA. Simulation results from the IEEE 68 bus test system, a real 400 bus power system, and the IEEE 39 bus test system with an embedded HVdc transmission system demonstrate that the proposed method is suitable for large ac networks with power electronic devices. The results demonstrate good agreement between the proposed method and electromagnetic transient (EMT) simulation. The results also demonstrate that the proposed method is fast and scalable with CPU times that are up to 200 times faster than EMT simulation. [ABSTRACT FROM AUTHOR]

This paper presents a unified power flow algorithm for large and complex mixed ac/dc power systems based on the partitioning of power grids, a version of the two-level Newton method, and the modified nodal analysis formulation. Partitioning significantly increases numerical efficiency without altering the accuracy of the power flow solution. This approach can be applied to any combination of multiple dc and possibly non-synchronized ac systems. It considers the steady-state interaction of ac and dc systems for a wide range of converter representations and control functions. Simplification of elements within the converter stations is not required. Both dc and ac-side converter losses are adequately accounted for by using a generalized converter loss model. The steady-state converter equations are derived in their most general form, with the ac and/or dc-side power exchange or voltages defined as controlled quantities. [ABSTRACT FROM AUTHOR]

Practical superconducting quantum interference devices (SQUIDs) have been developed into multiloop hybrid electric circuits with Josephson junctions and normal elements such as resistor, inductor and capacitor. To find a common circuit analysis and simulation method for different types of SQUID hybrid circuits consist of both superconducting and normal components, we introduce a mesh-current method, which can derive both the general system model and uniform circuit equations directly from the equivalent circuit. The mesh-current method is demonstrated in the simulation of a SQUID additional positive feedback circuit. The numerical simulation results are presented and verified with the measurements. Compared with the conventional nodal analysis method, the mesh-current method is excellent in dealing with the relations including external flux, self and mutual inductances in multiloop hybrid circuit analysis; its final circuit equations directly exhibit the physical theorems; its general system model reveals the quantum interference mechanism inside SQUID circuits, and is applicable for further dynamics studies. [ABSTRACT FROM AUTHOR]

We present an enhanced partial element equivalent circuit (PEEC) model based on Voronoi decomposition of triangular meshes. A complex geometry is accurately represented by many surface triangles, while keeping the number of elements in the corresponding equivalent circuit far less than the number of triangles. To do this, the triangular geometry is automatically decomposed into surface partitions using Voronoi's algorithm. These partitions describe capacitance cells, while inductance elements are set between all neighboring partition pairs. The inductance (L) and capacitance (C) matrix calculations are done independently using solvers based on quasi-static electric and magnetic full-wave method of moments (MoM). To get the current and charge distribution over the triangles, the MoM results during LC evaluation are combined with the results of modified nodal analysis. We validated our method against the standard PEEC and MoM results as well as measured data. Then, we used our method to simulate conducted emission for a real automotive LED brake-light module. [ABSTRACT FROM AUTHOR]

This article presents the improved formulations for the latency insertion method (LIM) for diodes and MOSFETs utilizing the voltage-in-current framework. LIM is a fast circuit simulation algorithm, which computes the solutions to the voltages and currents in a circuit in a leapfrog manner, instead of a simultaneous matrix solution typically performed in the modified nodal analysis formalism. This allows LIM to have a far superior scaling with respect to the dimensions of the circuit. The formulations presented here have the advantage of not being limited by the stability condition in LIM and thus allow the simulations to be performed at larger time steps. Numerical examples are presented, which illustrate the improved performances of the developed formulations. [ABSTRACT FROM AUTHOR]

Adding mushroom-like electromagnetic band-gap (EBG) structures to split power planes can produce wideband suppression of ground bounce noise in high-speed printed circuit boards. Practical equations are used to estimate the stop-band performance of EBG structures within parallel power planes. In this article, a mushroom-like EBG and power-bus structure are derived using the modified nodal analysis (MNA) method. Equations calculated using the MNA method are easily programmable. The partial EBG structures developed in this article can suppress noise from electromagnetic (EM) interference within parallel plates in the power bus. Several examples below show that similar results can be obtained in measurements, in EM simulations software, and in derived equations. The proposed structure enhanced the suppression of simultaneous switching noise coupling (≤−40 dB) within the range of 260 MHz to 10 GHz. [ABSTRACT FROM AUTHOR]

Tensioned cable nets can be used as a lightweight supporting formwork in the construction of thin concrete architectural shells. Meeting the structural and mechanical specifications of such shells requires precise positioning of the nodes of the cable net. We develop and experimentally verify a control strategy that uses measurements of the nodal positions to identify model parameters and calculate adjustments to the boundary cable lengths to achieve the desired form. As cable net lengths adjustments on the construction site are time-consuming, the number of control adjustments is minimized via a sparsity-promoting optimization-based method. [ABSTRACT FROM AUTHOR]

This paper focuses on the interchange and generation scheduling problem of multi-area power systems, where decentralized decision procedure is preferred and the uncertainties of nodal injections should be considered. The problem is formulated as a multi-area robust security constrained unit commitment model, with a novel uncertainty set specified by the variance of system net load. We prove that such an uncertainty set can provide a more precise probabilistic guarantee than conventional budgeted sets. To solve the problem in decentralized manner, an upper-level robust convex optimization model is proposed to optimize the tie-line power flow and derive a generation interval for each area. Then through the coordinated uncertainty requirement decided by the generation interval, each regional system operator can solve a decoupled robust unit commitment problem independently. Besides, a modified outer approximation algorithm is developed to obtain higher-quality solution of the bilinear programming involved in the process. Simulation results on a two-area system demonstrate the effectiveness of the uncertainty set, and show the economic efficiencies of unit commitment solutions acquired from the hierarchical method. [ABSTRACT FROM AUTHOR]

In this paper we present a solution for real-time multi-FPGA simulation of energy conversion systems based on the Latency-Based Linear Multistep Compound (LB-LMC) simulation approach. The approach relies on a nodal decomposition approach derived from multiport network analysis, and fast parallel communication between Field Programmable Gate Array (FPGA) devices. The results presented in this paper –using a microgrid example– demonstrate how the developed real-time platform overcame the resource scalability limit of single FPGA solvers while achieving a time step size of 100 nanoseconds. [ABSTRACT FROM AUTHOR]

This paper presents an FPGA-based Digital Real-Time Simulation (DRTS) environment for the analysis of Electromagnetic Transients (EMTs) of power systems that include multiple Power Electronic Converters (PECs). The main features of the proposed DRTS platform are that it i) employs two-value resistor switch model for PECs and thus avoids inaccuracies of Associate Discrete Circuit (ADC) model and ii) does not require separation of PECs by transmission lines (stub lines) and thus accurately represents PECs in close electrical proximity of each other. These features respectively result in a time-variant and large system admittance matrix which significantly increases the computation burden in each simulation time-step and can render it infeasible for real-time applications. To overcome this problem this paper introduces i) Switching-Network Partitioning (SNP) method which is tailored for PECs representation in FPGA and ii) Reformulated Modified Nodal Analysis (RMNA) method to enable computational parallelism between the solution of network and component models in FPGA. SNP enables solution-level partitioning of the PECs and the rest of the system. The developed DRTS platform enables sub-microsecond simulation time-step and provides a fixed hardware irrespective of the system configuration. Performance of the platform is evaluated for a study system and verified versus off-line simulation studies. [ABSTRACT FROM AUTHOR]

Real-time tracking and identification of Thevenin equivalent parameters is crucial for voltage stability online monitoring of large power grids. An online parameter identification method based on wide-area measurements and nodal analysis is proposed in this paper. The node-voltage equation is utilized directly, and the open-circuit voltage is calculated accurately as the Thevenin equivalent voltage of load buses. Moreover, the equivalent parameters can be identified precisely under the generator reactive power over-limit condition. To avoid repetitive Gaussian elimination of the high-dimensional linear system, lower upper factorization and optimized substitution are used to accelerate the open-circuit voltage solution process. The simulation results of multiple test systems demonstrate the accuracy and rapidity of the proposed method. [ABSTRACT FROM AUTHOR]

Assembly of power-flow equations has traditionally begun from a nodal analysis formulation of the underlying transmission circuit's behavior. Most power-flow formulations encapsulate network constraints in the bus admittance matrix, $Y_{\text{bus}}$. From a circuit perspective, this admittance representation restricts the network elements to be voltage controlled; resulting drawbacks treating zero-impedance branches in such applications as state estimation have long been recognized. This paper explores the advantages of the alternatives to $Y_{\text{bus}}$ -based formulations in power flow. It proposes a sparse tableau formulation (STF), and it demonstrates its computational efficiency, robustness, and generality in detailed comparison to traditional $Y_{\text{bus}}$ -based solution algorithms. In the examples of power networks ranging from 1888 to 82 000 buses, computational case studies indicate that STF provides comparable computational speed, while allowing simple treatment of zero-impedance branches and more reliably converging to solutions in many cases for which $Y_{\text{bus}}$ -based Newton algorithms diverge. [ABSTRACT FROM AUTHOR]

In this paper, a simplified model of a 2 × 25 kV bi-level traction power system for feeding high-speed trains is presented. A modified nodal analysis (MNA) based algorithm for solving the system with and adaptive damping factor is also explained. The main novelties of this paper are the inclusion of train protections (over-current and over-voltage) in the model and the development of the MNA solving procedure that increases the stability and robustness of the iterative solving process. Another important feature of the model is that it can be easily adapted to a single voltage feeding systems by deactivation of specific parameters. The accuracy and performance of the proposed simulator is compared and verified relative to the derivative based solvers. [ABSTRACT FROM AUTHOR]

Objective: We aim to improve operational robustness of liquid scanning probes. Two main failure modes to be addressed are an obstruction of the flow path of the processing liquid and a deviation from the desired gap distance between probe and sample. Methods: We introduce a multi-functional design element, a microfluidic bypass channel, which can be operated in dc and in ac mode, each preventing one of the two main failure modes. Results: In dc mode, the bypass channel is filled with liquid and exhibits resistive behavior, enabling the probe to passively react to an obstruction. In the case of an obstruction of the flow path, the processing liquid is passively diverted through the bypass to prevent its leakage and to limit the buildup of high pressure levels. In ac mode, the bypass is filled with gas and has capacitive characteristics, allowing the gap distance between the probe and the sample to be monitored by observing a phase shift in the motion of two gas–liquid interfaces. For a modulation of the input pressure at 4 Hz, significant changes of the phase shift were observed up to a gap distance of 25 μm. Conclusion: The presented passive design element counters both failure modes in a simple and highly compatible manner. Significance: Liquid scanning probes enabling targeted interfacing with biological surfaces are compatible with a wide range of workflows and bioanalytical applications. An improved operational robustness would facilitate rapid and widespread adoption of liquid scanning probes in research as well as in diagnostics. [ABSTRACT FROM AUTHOR]

This paper presents a novel data-driven method that determines the daily consumption patterns of customers without smart meters (SMs) to enhance the observability of distribution systems. Using the proposed method, the daily consumption of unobserved customers is extracted from their monthly billing data based on three machine learning models. In the first model, a spectral clustering algorithm is used to infer the typical daily load profiles of customers with SMs. Each typical daily load behavior represents a distinct class of customer behavior. In the second module, a multi-timescale learning model is trained to estimate the hourly consumption using monthly energy data for the customers of each class. The third stage leverages a recursive Bayesian learning method and branch current state estimation residuals to estimate the daily load profiles of unobserved customers without SMs. The proposed data-driven method has been tested and verified using real utility data. [ABSTRACT FROM AUTHOR]

A new circuit-field coupling methodology for a single-phase transformer connected to a half-wave rectifier is presented. The rectifier is composed of switched electronic devices (EDs) which can be modeled through a piecewise-linear approximation technique. The modified nodal analysis (MNA) is used to solve the circuit where the EDs are represented with stamps that are systematically incorporated into the system of differential equations. The transformer is modeled using a 2-D finite-element (FE) approach, leading to a coupled circuit-field system, which is solved using proprietary software. The system is also implemented experimentally using an xPC-Target data acquisition system, showing close correspondence with simulation results. Thus, this paper provides the basis for implementing multi-level power converters connected to transformers. [ABSTRACT FROM AUTHOR]

In this paper, the focus is on the efficient solution of magnetic equivalent circuits that include relative motion between components. It is shown that by combining the use of mesh and nodal analysis, one can avoid the need to restructure the circuit topology, which is a step encountered in strictly mesh-based approaches. In addition, one can overcome the poor convergence properties observed in strictly nodal-based formulations. A scaling of variables is introduced to ensure the condition that the number of the mixed mesh/nodal matrices remains relatively low. The proposed scaled model structure is then extended to magnetic equivalent circuits that are coupled to electrical systems for the analysis of dynamic performance. It is shown that the numerical properties of the coupled scaled model remain strong. [ABSTRACT FROM AUTHOR]

Graph is an important data representation which appears in a wide diversity of real-world scenarios. Effective graph analytics provides users a deeper understanding of what is behind the data, and thus can benefit a lot of useful applications such as node classification, node recommendation, link prediction, etc. However, most graph analytics methods suffer the high computation and space cost. Graph embedding is an effective yet efficient way to solve the graph analytics problem. It converts the graph data into a low dimensional space in which the graph structural information and graph properties are maximumly preserved. In this survey, we conduct a comprehensive review of the literature in graph embedding. We first introduce the formal definition of graph embedding as well as the related concepts. After that, we propose two taxonomies of graph embedding which correspond to what challenges exist in different graph embedding problem settings and how the existing work addresses these challenges in their solutions. Finally, we summarize the applications that graph embedding enables and suggest four promising future research directions in terms of computation efficiency, problem settings, techniques, and application scenarios. [ABSTRACT FROM AUTHOR]

The modular multilevel matrix converter (M3C) is a promising topology for high-voltage high-power applications. It features easy scalability, high-quality input and output waveforms, superior availability, etc. This letter aims to further increase the availability of the M3C when one or more of the nine branches are lost. A general nonlinear multivariable optimization model is set up to optimize the branch current configuration after the branch lost. The proposed method reduces system power capability loss after the branch failure. It achieves a smooth transition from a full M3C to a reduced topology without shutdown of the system. A M3C prototype with 27 cells is designed, and experiment results are presented to confirm the validity of this method. [ABSTRACT FROM AUTHOR]

Recent studies in wireless scheduling have shown that carrier-sense multiple access (CSMA) can be made throughput optimal by optimizing over activation rates. However, those throughput optimal CSMA algorithms were found to suffer from poor delay performance, especially at high throughputs where the delay can potentially grow exponentially in the size of the network. Motivated by these shortcomings, in this paper we propose a node-based version of the throughput optimal CSMA (NB-CSMA) as opposed to traditional link-based CSMA algorithms, where links were treated as separate entities. Our algorithm is fully distributed and corresponds to Glauber dynamics with “Block updates”. We show analytically and via simulations that NB-CSMA outperforms conventional link-based CSMA in terms of delay for any fixed-size network. We also characterize the fraction of the capacity region for which the average queue lengths (and the average delay) grow polynomially in the size of the network, for networks with bounded-degree conflict graphs. This fraction is no smaller than the fraction known for link-based CSMA, and is significantly larger for many instances of practical wireless ad-hoc networks. Finally, we restrict our focus to the special case of collocated networks, analyze the mean starvation time using a Markov chain with rewards framework and use the results to quantitatively demonstrate the improvement of NB-CSMA over the baseline link-based algorithm. [ABSTRACT FROM AUTHOR]

A new augmented electric field integral equation (A-EFIE) formulation is discussed in the low frequency. In the new formulation, both the electric current and charge are considered as unknowns. Different from the conventional A-EFIE, a constraint on the normal component of the magnetic field is added to modifying the formulation of A-EFIE for improving the accuracy and a kind of constant nodal functions is introduced for expanding the electric charge. With the proposed method, besides avoiding the low-frequency breakdown, the storage of impedance matrix is reduced over 35% compared with the conventional A-EFIE, which is owing to the application of constant nodal functions associated with vertices. Numerical examples illuminate the validity and performance of the new A-EFIE with constant nodal functions. [ABSTRACT FROM PUBLISHER]

A generic small-signal model of modular multilevel converter (MMC) based DC grid is established and a DC virtual impedance damping control to suppress the resonance and instability is proposed. The averaged-value model (AVM) of MMC is employed to derive the Thévenin equivalent model of the converter from its DC side using the power-balancing principle considering the dynamics of phase-locked loop (PLL) of the interconnected ac system. The single section π-typed line model is selected to develop the nodal admittance equations of the DC network in s domain. The stability criterion of the DC grid is given after establishing the generic linearization model. The key factors affecting the DC grid's stability are identified using the root locus method and participation factors analysis. The parameters and the performances of the damping controller are designed and studied. Electromagnetic transient simulation model and RT-LAB real-time simulation are used to validate that the proposed damping control can suppress the instability of the DC grid and improve its operating performance. [ABSTRACT FROM PUBLISHER]

The voltage solution of DC railway traction power networks is classically obtained via the current injection (CI) method, which is based on solving a sequence of nodal voltage equations. Specialized techniques, which build on the CI method, have been proposed for simulating limited network receptivity due to voltage rise constraints and nonreversible substations. These techniques may require a multitude of power reduction steps for modeling the local controller operation of trains in regenerative braking mode, and they consequently lead to a large computational effort. This paper proposes a sensitivity-based approach for computing the regenerative train power that can be returned to the network without causing over voltage. In the case of nonreceptive substations, each regenerating train is switched to a voltage–current source model and the CI method is used to further adjust the power that can be received by the network; a two-phase approach is used to compute the regenerative train resistance without recourse to iterations. The proposed method is tested on network models with branched lines, detailed return circuits, and having up to 144 trains. The computational performance comparisons show that the proposed method for simulating local controllers can be significantly faster than the classical power reduction method. [ABSTRACT FROM PUBLISHER]

Most performance metrics in wireless networks, such as outage probability, link capacity, etc., are functions of the distances between communicating/interfering nodes. A probabilistic distance-based model is definitely needed in quantifying these metrics, which eventually involves the nodal distance distribution (NDD) in a finite network intrinsically depending on the network coverage and nodal spatial distribution. Recently, the NDD from a reference node to a uniformly distributed node has been extended to the networks in the shape of arbitrary polygons. In contrast, the NDD between two uniformly distributed nodes (Ran2Ran) is still confined to the networks in certain specific shapes, including disks, triangles, rectangles, rhombuses, trapezoids, and regular polygons, which greatly limits its applicable network scenarios. By extending a tool in integral geometry, called Kinematic Measure, and using decomposition and recursion methods, this paper shows a systematic, algorithmic approach to Ran2Ran NDDs, which can handle arbitrarily-shaped networks, including convex, concave, disjoint, and tiered networks. Besides validating our approach through extensive simulations and comparisons with the known results if applicable, we also demonstrate its potentials in handling nonuniform nodal distributions, and in modeling two wireless networks of particular interest in the current literature, where the existing approaches are inapplicable. [ABSTRACT FROM PUBLISHER]

A general and systematic formulation based on the finite-element method, modified nodal analysis and multi-field system approach is presented for the analysis of multiple magnetic field systems that are electrically interconnected through circuit networks in the frequency domain. This approach permits simultaneous solution of any number of 2-D Cartesian and axisymmetric problems by considering the electrical terminals of each finite-element model as nonnatural elements of the modified nodal analysis, allowing their systematic incorporation into the global system of equations. This way, arbitrary electrical network topologies can be readily analyzed, where the magnetic systems are no more than simple elements of the circuit system. Moreover, a unified building block is introduced for the 2-D and axisymmetric models, leading to easy computer implementation. The effectiveness of our formulation is tested by determining the electromagnetic behavior of a double-squirrel cage induction motor that is connected to three feeding transformers. A 2-D Cartesian finite-element model is employed for the three-phase motor, whereas an axisymmetric representation is used for each transformer. Hence, four finite-element models are simultaneously solved, which are electrically coupled through circuit elements. Lumped circuit parameters model the end effects of the motor squirrel cage and stator as well as the associated stator feeding circuits. Previous work only considers coupling of Cartesian systems, while our formulation expands the capabilities of quasi-3-D finite-element modeling by systematically coupling 2-D and axisymmetric finite-element models. [ABSTRACT FROM PUBLISHER]

Electromagnetic transient-type (EMT-type) programs solve nodal analysis or modified-augmented-nodal-analysis (MANA) formulation-based power system network equations (PSNE). The PSNE coefficient matrix can be either constant or time varying depending on the utilized synchronous machine (SM) model. Therefore, a computational efficiency comparison for the SM models requires accounting for the refactorization scheme and the utilized sparse matrix solver (SMS). In addition, MANA formulation does not require or force admittance model usage and enables flexibility while representing the SMs in PSNE. This paper compares computational performances of various SM models for a practical case and accounts for the refactorization scheme, the utilized SMS, and the SM representation in MANA formulation. [ABSTRACT FROM PUBLISHER]

This paper presents a simple method for voltage stability assessment by reducing the bus impedance matrix of a network into its two-bus equivalent model at a referred bus. Closed-form equations of the equivalent model could then be derived to facilitate an equivalent nodal analysis at the referred bus to determine its voltage stability limit. The method was also shown to have parallels with the well-accepted modal analysis of the Jacobian matrix. These include defining geometric indices to identify critical buses and participation factors to quantify contribution of network elements to their criticality. The method however does not require post power flow solution processing of the Jacobian matrix; such computational advantage may make it suitable for online applications. The IEEE 300-bus system was tested with the method which was shown to be valid and computationally robust and efficient. [ABSTRACT FROM AUTHOR]

This paper presents a symmetrical components approach for computing the phase-coordinates nodal admittance matrices of three-phase transformers, where each connection is comprised either of three single-phase units or one three-phase unit. The approach is based on assembling the symmetrical component circuits into the different three-phase connections; it can straightforwardly handle unsymmetrical transformer banks with different phase electrical characteristics or missing phases, and grounding impedances. The proposed approach easily accounts for the various clock numbers quoted in the British Standard (BS) and the International Electrotechnical Commission (IEC) Standard on power transformers; this presents an advantage as compared to classical phase-coordinates approaches that require defining a distinct connection matrix corresponding to each transformer vector group. [ABSTRACT FROM AUTHOR]

In this paper, an alternative perspective on the transmission line modeling (TLM) method concepts to unify previous work is presented. The procedure begins by discretizing Maxwell’s equations and proposing TLM equivalent models. Node voltage and mesh current definitions are provided in terms of link line contributions, compatible with stub currents and voltages. They allow obtaining an expression that relates incident and reflected pulses with no other condition required. With this unified approach, modeling of other situations is straightforward. 2-D cases, source implementation, and anisotropic media are described and numerically tested. [ABSTRACT FROM AUTHOR]

This paper presents photovoltaic-oriented nodal analysis (PVONA), a general and flexible tool for efficient spatially resolved simulations for photovoltaic (PV) cells and modules. This approach overcomes the major problem of the conventional Simulation Program with Integrated Circuit Emphasis-based approaches for solving circuit network models, which is the limited number of nodes that can be simulated due to memory and computing time requirements. PVONA integrates a specifically designed sparse data structure and a graphics processing unit-based parallel conjugate gradient algorithm into a PV-oriented iterative Newton–Raphson solver. This first avoids the complicated and time-consuming netlist parsing, second saves memory space, and third accelerates the simulation procedure. In the tests, PVONA generated the local current and voltage maps of a model with $316 \times 316$ nodes with a thin-film PV cell in 15 s, i.e., using only 4.6% of the time required by the latest LTSpice package. The 2-D characterization is used as a case study and the potential application of PVONA toward quantitative analysis of electroluminescence are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a global method of evaluating nodal eddy currents based on the known nodal potentials, which is a Galerkin finite-element method formed by employing the Schaubert–Wilton–Glisson basis function as a weighting function. As a result, the accuracy of eddy-current evaluation in the railgun computation could be increased using the nodal finite-element method. The new method takes all the nodal potential values into account to obtain the global nodal current density directly by solving the finite-element equation, which could overcome the drawback of the traditional local element postprocessing method. The computational results show that the new method could greatly enhance the computational accuracy of eddy current, relative to the traditional element postprocessing method. This method could not only be used in the eddy-current evaluation of the railgun but also in other gradient field computations based on known nodal potential values. [ABSTRACT FROM PUBLISHER]

Effectively showing the relationships between objects in a dataset is one of the main tasks in information visualization. Typically there is a well-defined notion of distance between pairs of objects, and traditional approaches such as principal component analysis or multi-dimensional scaling are used to place the objects as points in 2D space, so that similar objects are close to each other. In another typical setting, the dataset is visualized as a network graph, where related nodes are connected by links. More recently, datasets are also visualized as maps, where in addition to nodes and links, there is an explicit representation of groups and clusters. We consider these three Techniques, characterized by a progressive increase of the amount of encoded information: node diagrams, node-link diagrams and node-link-group diagrams. We assess these three types of diagrams with a controlled experiment that covers nine different tasks falling broadly in three categories: node-based tasks, network-based tasks and group-based tasks. Our findings indicate that adding links, or links and group representations, does not negatively impact performance (time and accuracy) of node-based tasks. Similarly, adding group representations does not negatively impact the performance of network-based tasks. Node-link-group diagrams outperform the others on group-based tasks. These conclusions contradict results in other studies, in similar but subtly different settings. Taken together, however, such results can have significant implications for the design of standard and domain snecific visualizations tools. [ABSTRACT FROM PUBLISHER]

As very large scale integration circuit speeds and density continue to increase, 3-D electromagnetic methods have become essential for the analysis, design, and verification of high-speed systems. Since such models are commonly used inside standard circuit simulators for time or frequency domain computations, it is imperative to make them as compact as possible without compromising accuracy. To this aim, model-order reduction techniques can be successfully adopted. In this paper, we describe a partitioned Krylov subspace-based method for deriving reduced-order models directly from 3-D quasi-static partial element equivalent circuit models. The multiscale block decomposition method is adopted to speed-up the computation of the projection matrix; furthermore, the adaptive cross approximation and singular value decomposition techniques are used to achieve matrix compression exploiting the low-rank behavior of magnetic and electric field couplings. Results are presented on several examples to demonstrate the capabilities and speed of the proposed new method. [ABSTRACT FROM AUTHOR]

A novel fault diagnostic method based on node-voltage vector ambiguity sets for analog circuits is presented in this paper. The method uses a sinusoidal stimulus instead of a dc-based stimulus. It employs steady-state node-voltage responses on observable nodes under different fault conditions to establish node-voltage vector ambiguity sets for fault diagnosis. An ellipse-based measurement solution to measure node-voltage vectors is also described. A frequency selection algorithm for a sinusoidal stimulus is introduced. A fault diagnostic example based on the node-voltage vector ambiguity sets is presented. Finally, a programming strategy to extend the method to large-scale analogue circuit designs is described. [ABSTRACT FROM PUBLISHER]

In this paper, we show the efficiency and accuracy of an implicit time-domain solver for the nodal analysis of circuits generated by the partial element equivalent circuit method. The multiscale block decomposition, based on the recursive partitioned matrix inverse formula and compression techniques, is applied to the implicit time-domain solver in order to further speeding up the computations. The effectiveness of the proposed approach is confirmed by the numerical results. [ABSTRACT FROM PUBLISHER]