Transmission Line Modeling Method Research Articles

Transmission line modeling co-simulation with distributed delay-size control using steady-state identification

Combining performance and numerical stability is a key issue in co-simulation. The Transmission Line Modeling method uses physically motivated communication delays to ensure numerical stability for stiff connections. However, using a fixed communication delay may limit performance for some models. This paper proposes Steady-State Identification for enabling variable communication delays. Three algorithms for online Steady-State Identification are evaluated in three different co-simulation models. All algorithms are able to identify steady state and can thereby determine when communication delays can be allowed to increase without compromising accuracy and stability. The results show a reduction in number of the solver derivative evaluations by roughly 40–60% depending on the model. The proposed method additionally supports connections with asymmetric communication delays, which allows each sub-model to independently control the delay of its input variables. Models supporting delay-size control can thereby be connected to those that do not, so that the step length of each individual sub-model is maximized. Controlling the delay-size in sub-models also makes the method independent of the master co-simulation algorithm.

Research on Grid Information Model (GIM) Technology of Transmission Line Based on Full-area Feature Weight Template Matching Recognition

Aiming at the problems of low efficiency, poor spatial location and incomplete attribute information in current transmission line modeling methods, a refined modeling method for transmission lines based on full area feature weighted template matching is proposed. First, collect the point cloud of the scary line, and extract the point cloud data of the tower and power line; Secondly, statistical outlier filter is used to denoise point cloud data; Finally, the GIM model of the transmission line is constructed by using the whole region feature weighted template matching method, which realizes the integrity and lightweight of the geometric, appearance and semantic information of the three-dimensional model of the transmission line, improves the efficiency of the transmission line modeling, and is verified by taking a 500kV transmission line as an example.

Numerical study of heat transfer in high voltage solid insulating materials using transmission line method

PurposeThe purpose of this study is to numerically examine the heat transfer and transport of space charges in the solid insulating materials [low density polyethylene (LDPE), flame retardant type 4 (FR4), Polytetrafluoroethylene (PTFE)] using the transmission line modeling (TLM) method. Besides, a comprehensive study is performed on the mutual influences of heat transfer and space charges transport within the solid dielectric bulk.Design/methodology/approachThe obtained governing equations including continuity and circuit equations are coupled with heat transfer equations, and they are solved via fourth-order Runge–Kutta method.FindingsThe electric potential and field, current density and temperature distribution are calculated. It is shown that compared with FR4 and PTFE, the temperature increment rate in LDPE is much lower. Moreover, the heat transfer in the solid insulating materials bulk increases the homo-charges density and temperature in the vicinity of electrodes. Hence, the reduction in electric field is reflected in the potential deformations in the proximity of electrodes. Furthermore, where the electric field is maximized, the temperature is minimized.Research limitations/implicationsThis study is restricted to two-dimensional problems.Originality/valueInterestingly, because of the lower temperature in LDPE, the current density and their increment rates in LDPE are much lower than that in FR4 and PTFE dielectric materials.

Model Order Reduction for Real-Time FPGA-Based Finite Element Transient Simulation of Three-Phase Transformer

The finite element method (FEM) is commonly used in modeling the electromagnetic field of transformers with high accuracy; however, the computation time of the FEM is prohibitively high for real-time simulation due to high model order. Reducing the model order is helpful to improve the computational efficiency of the FEM. The proper orthogonal decomposition (POD) is an efficient method to reduce the linear model order but encounters difficulties with nonlinear models. In this paper, a model order reduction (MOR) method based on the combination of POD and the transmission-line modeling (TLM) is proposed to reduce the nonlinear finite element model order and computation time. The TLM method is used to separate the nonlinear components from the model, and then the POD is used to reduce the linear domain order of the model. The nonlinear components obtained by TLM can be solved in parallel on the field programmable gate array (FPGA) to improve computational efficiency further. This paper has studied the transient states of a three-phase transformer with the current excitation and field-circuit coupling. The real-time hardware emulation results are validated by results from offline simulation using Comsol®.

Two-Dimensional Thermal Diffusion Equation Solver Based on Unstructured Transmission-Line Modelling and Optimal Delaunay Triangular Meshes

The transmission-line modelling (TLM) method has been widely applied to many areas including electromagnetic and heat conduction problems. Its unstructured version, unstructured TLM (UTLM), however, has not hitherto been fully exploited in thermal diffusion problems. This paper derives in detail a thermal UTLM scheme to solve the two-dimensional diffusion equation numerically based on the optimal Delaunay triangular (ODT) mesh.

Design and analysis of an InGaAs/InGaAsP quantum well microlaser with longitudinal periodical strain distribution for single-mode lasing.

Single-mode lasing for small size semiconductor laser is significantly important in the on-chip optical signal processing, data storage, and dense optical integrated systems. This paper presents new, to the best of our knowledge, single-mode quantum well microlasers by distributing periodical strain along the longitudinal laser cavity. The quantum transmission line modeling (Q-TLM) method is employed to establish the model for strained microlasers. The dynamic output of quantum well microlasers with longitudinal periodical strain (LPS) distribution is analyzed in the time and frequency domains, and it is found that the introduction of LPS significantly improves the single-mode output of quantum well microlasers by increasing the side mode suppression ratio (SMSR) from 8.44 to 28.29 dB. The study results confirm that well-controlled periodical strain along the longitudinal laser cavity provides an alternative routine for realizing single-mode lasing by strain engineering.

Construction of 3D Scene of Transmission Line Corridor Based on GIM and 3D GIS

Transmission lines have the characteristics of strip distribution, wide coverage, and close connection with the actual geographical environment. The traditional transmission line modeling method has the defects of insufficient spatial positioning ability and weak information expression ability. Therefore, in this paper, three-dimensional geographic information system (3D GIS) and grid information model (GIM) are coordinated to make the two complementary advantages and construct the three-dimensional scene of transmission line corridor. First, The visible light images and high-precision laser point cloud data of transmission line corridor are collected by helicopter, and extract power lines and towers from the laser point cloud data. Then, the oblique photogrammetric model of large-scale scene is made from visible light images and modified. Finally, according to the point cloud of power line and tower, the improved template matching method is used to realize the rapid modeling of transmission line GIM model, and the transmission line model is obtained. A complete 3D digital twin scene model of transmission line corridor is formed by fusing scene model and transmission line model. The research results show that the 3D scene construction method of transmission line corridor based on 3D GIS and GIM not only improves the efficiency of transmission line modeling, but also has a good visual effect. The abundant line information is helpful for the visual operation and maintenance management of existing transmission lines from macro to micro, which provides data support for the construction of digital power grid.

Thermal Effects of 5G Frequency EM Waves on Ocular Tissue

This research article aims to investigate the thermal effects on human eye due to exposure of EM (electromagnetic) field at 5G frequencies. A secondary purpose of the article is to show that SPICE, one of the most commonly used tools in circuit analysis, can be used to solve complex EM and bioheat transfer problems. Both electric field and temperature distributions in human eye are simulated with transmission line modelling (TLM) method. Also, finite element method (FEM) calculations are carried out for comparison. Temperature distributions are calculated for 30 minutes of EM radiation exposure. As a subject of the simulation, a human is chosen that the power density of incoming field at the human eye is assumed as the maximum of the ICNIRP general public exposure limits. A good consistency between TLM and FEM based simulations is found. A new transmission line model based on Debye parametric model is generated for simulation of EM field distribution in the tissues. With this generated transmission line, the results for the frequencies of interest can be obtained via single simulation. Also, a new transmission line model is developed for the temperature distribution simulation in which the effects of noncompressible fluid flow such as non-unidirectional blood flow in tissues and flow in aqueous humor are taken into consideration.

A New ADE-TLM for Lorentz Dispersive Medium

We present a new numerical algorithm for the simulation of dispersive media. This model named ADETLM is based on the transmission line modeling method with the symmetrical condensed node (SCNTLM) and novel voltage sources and exploits the polarization current density J along with the voltage electric as well as the average approximation. We extend the proposed algorithm to media with dispersions described by multiple second-order Lorentz poles; the obtained results of the reflection and transmission coefficients are compared with analytical solutions.

Operation analysis of the wideband high-power microwave sources based on the gyromagnetic nonlinear transmission lines.

The wideband High-Power Microwave (HPM) sources, which combine the advantages of narrowband and ultrawideband sources, have drawn much attention. As a kind of wideband source, the gyromagnetic nonlinear transmission lines (GNLTLs) can directly modulate the incident pulses into radio frequency pulses without relying on the interaction between e-beam and microwaves. Due to the special working mechanism of gyromagnetic precession, the center frequency of the GNLTL can also be adjusted in a certain range. Based on classical magnetism and a simplified model of the GNLTL, this paper semi-quantitatively and theoretically analyzed the generation mechanism of HPM and illustrated the influences of the variations of parameters on the output microwaves. Then, a simple simulation based on 1-dimensional transmission line modeling method was carried out to study the performance of the GNLTL quantitatively, with the coupling of 1D telegraphist equations and the 3D Landau-Lifshitz-Gilbert equation. Simulation results preliminarily verified the conclusions derived from the theoretical analysis, and some working characteristics of the GNLTL were also obtained. This paper may help to understand the special working mechanism of the GNLTL and provide certain guidance for related simulations and experiments.

Time-Stepped Finite-Element Modeling of Three-Phase Transformer for Electromagnetic Transient Emulation on FPGA

The finite-element analysis is a powerful method to obtain detailed insight into the operation of any electromagnetic equipment. However, the required computational power to solve a finite-element modeled power equipment is so heavy that most Newton-Raphson-method-based algorithms can barely achieve real-time simulation. The low latency and hardware parallelism of the field-programmable gate array (FPGA) provides a path forward. In this paper, a parallel and deeply pipelined adaptive transmission-line modeling method with preconditioned conjugate gradient solver is designed in hardware and implemented on two Xilinx <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> XCVU37P FPGAs for the finite-element modeling of a three-phase transformer. The accuracy of the transformer solver under both current-excited and voltage-excited conditions of the transformer was validated against the commercial FE simulation tool.

Non-uniform strained quantum well amplifiers for multichannel optical signal amplification in the WDM system

This paper presents a new longitudinal non-uniform compressively strained quantum well amplifier for multichannel optical signal amplification in the wavelength division multiplexing (WDM) system. Quantum transmission line modelling (Q-TLM) method is adopted to analyse the scattering spectra of electron transitions as well as the gain spectrum of QW-SOAs. It is found that the electron scattering spectrum exhibits blue shift and reduced magnitude with the decrease of carrier density while there exists red shift and enhanced magnitude with the increase of compressive strain. Furthermore, it is found that the effects of decreased carrier density on the wavelength and bandwidth of the QW-SOA gain spectrum can be compensated by increasing compressive strain. Based on the theoretical analysis, the longitudinal non-uniform (linearly and Gaussian-distributed) compressively strained quantum well amplifiers are proposed. Multichannel and dense multichannel optical signal amplification in the proposed QW-SOAs are studied and it is found that distributing non-uniform compressive strain along the quantum well amplifier cavity can effectively improve the output performance of QW-SOAs by increasing the amplification amplitude and bandwidth. The quantum well amplifier with Gaussian strain distribution has a better output spectral property for multi-channel optical signal amplification in the WDM system. These studies provide important guidance to optimize the multichannel optical signal amplification in semiconductor optical amplifiers by the band engineering.

An Effective Stretched Coordinate TLM-PML Suitable for Analyzing Planar Periodic Structures

In this letter, the effectiveness of a recently developed stretched coordinate (SC) perfectly matched layer (PML) formulation in the transmission line modeling (TLM) method is investigated for truncating the out-of-plane computational domain of different unit-cell-based frequency selective surface (FSS) simulations. Transmitted power is compared against various absorbing boundary conditions; the accuracy of each method is determined by benchmarking against results from method of moments (MoM) simulations. Good agreement with the MoM analysis is shown by the SC TLM-PML and, unlike the weakly stable split-field-based TLM-PML schemes, no instabilities are observed in the late time.

Quantum Transmission Line Modeling and Experimental Investigation of the Output Characteristics of a Terahertz Quantum Cascade Laser

We describe a new approach to modeling the optoelectronic properties of a terahertz-frequency quantum cascade laser (THz QCL) based on a quantum transmission line modelling (Q-TLM) method. Parallel quantum cascade transmission line modeling units are employed to describe the dynamic optical processes in a nine-well THz QCL in both the time and frequency domains. The model is used to simulate the current–power characteristics of a QCL device and good agreement is found with experimental measurements, including an accurate prediction of the threshold current and emitted power. It is also confirmed that the Q-TLM model can accurately predict the Stark-induced blue shift of the emission spectrum of the THz QCL with increasing injection current. Furthermore, we establish the new Q-TLM model to describe the properties of a THz QCL device incorporating a photonic lattice patterned on the laser ridge, by linking the transmission line structure to each scattering module. The predicted effects of the lattice structure on the steady-state emission spectra of the THz QCL, including the side-mode suppression, are found to be in good agreement with experimental results. Our Q-TLM modeling approach is a promising tool for the future design of THz QCLs and analysis of their temporal and spectral behaviors.

Electrical and Optical Characteristics of Two-Dimensional MoS₂ Film Grown by Metal-Organic Chemical Vapor Deposition.

Atomically thin molybdenum disulfide (MoS₂) films were synthesized on a SiO₂/Si substrate by metal-organic chemical vapor deposition (MOCVD). Raman spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy studies reveal the double-atomic-layer structure and the surface element composition of the MOCVD-grown MoS₂ films. The photoluminescence measurement demonstrates a strong emission peak with a bandgap of 685.1 nm, attributed to highly efficient radiative transition at the double atomic layer. The contact resistance between the doubleatomic-layer MoS₂ film and metal electrode was measured using the transmission-line modeling method. A Ti/Au electrode forms an ohmic contact with the double-atomic-layer MOCVD-grown MoS₂ film, exhibiting a resistivity of 100 kΩ. The field-effect transistor based on the double-atomiclayer MoS₂ film exhibits an electron mobility of 1.3×10-4 cm²/V·s and an on/off ratio of 6.5×10² at room temperature.

Stretched‐coordinate PML in 2D TLM simulations

A novel implementation of the stretched coordinate perfectly matched layer (PML) is presented for the two-dimensional (2D) transmission line modelling (TLM) method. The formulation offers a unified approach and is based on the mapping of the TLM node to a complex stretched domain for which the resulting transformation of the constituent RLC transmission line components is elaborated. The transformation is shown to modify the TLM connect-scatter algorithm. The absorption performance is demonstrated by simulating a canonical waveguide test case. Unlike the existing split-field based TLM-PML implementations, which are better suited to lossless media, the numerical results obtained show the proposed PML formulation is effective in the termination of both lossy and lossless media.

A Complex Domain Mapping of the SCN for an Effective PML Implementation in TLM

An improved implementation of the perfectly matched layer (PML) is developed for the Transmission Line Modelling (TLM) method based on a mapping of the symmetrical condensed node (SCN) to an analytically extended geometric space. By mapping the TLM node, a medium – circuit equivalence is developed which maps transmission line parameters from real to complex domain. This consequently modifies the TLM scatter-connect process. The PML implementation is demonstrated for canonical cases where it is shown to have a comparable absorption performance and a significantly improved temporal stability relative to previously published TLM-PML formulations.

Applying Massively Parallel Computing to Multiscale Ka Dual-Band Transmit-Array Analysis Using FETI-2LM

Transmit-arrays (TAs) are a popular cost-effective solution for high-gain antennas at millimeter waves. The design of these antennas relies on the fine tuning of the subwavelength unit cells that compose the aperture. The intricacy of the unit cells increases as new features are implemented, such as dual-band operation and wide-angle beam steering, making this antenna even more computationally challenging. In this article, a high-gain (25 dBi @ 20 GHz and 28 dBi @ 30 GHz) multiscale Ka dual-band TA for beam-steering applications is analyzed using a massively parallel implementation on multicores clusters of the finite element tearing and interconnecting method, with a two Lagrange multiplier (FETI-2LM) technique. The main contribution of this article is the implementation of 3-D nonperiodic grids with subdomains of different scales, that is suitable for proper modeling of different regions of the antenna (horn feed, lens cells, and air region). An automatic batch file procedure is proposed for the TA meshing, allowing the limited set of constitutive unit cells of the TA to be meshed separately. Additionally, we are using a block-Krylov strategy to efficiently capture the TA beam-steering capability, without restarting from scratch the interface problem for each feed position. Since other finite element method results were not accessible due the size of the problem, the FETI-2LM numerical results provided in this article are compared with other multilevel fast multipole methods and transmission line modeling method of CST Microwave Studio solvers, as well as with the measured results of the corresponding Ka dual-band prototype. The computational infrastructure has been used only a fraction of its capacity. Therefore, a much higher gain design (40 dBi) can be assessed, opening a new realm of applicability of TAs in the space segment usually occupied by reflector-based solutions.

Simulation of space charge transport in solid dielectric materials using transmission lines modeling method

In this paper, a lumped RC circuit model, which is based on the Transmission Line Modeling (TLM) method, is used to describe the space charge production and displacement mechanisms in three different solid dielectric materials (LDPE, PTFE and FR4). Each dielectric material is considered as a transmission line with the capacitive and resistance elements. The obtained circuit equations are solved along with the continuity equations for the various charged species in the bulk of solid dielectric material. The electric potential and field, density of different charged species and their recombination rates, resistive and capacitive properties of the solid dielectric material are calculated. In addition, the effects of the variations in the applied voltage, dielectric permittivity and temperature on these physical parameters are examined. Besides, compared with LDPE and PTFE, the net charge density increment rate in FR4 is much higher. Moreover, the influences of temperature on the net charge density in LDPE are not significant. Furthermore, at the higher applied voltages, the current density is increased. Interestingly, the effects of temperature variations on the recombination rates, net charge and current density in LDPE are much lower. Hence, the suitability of LDPE as solid dielectric material is proved.

Real-Time HIL Emulation of Faulted Electric Machines Based on Nonlinear MEC Model

In electric machine drive systems, hardware-in-the-loop (HIL) emulation provides accurate testing of actual control system prototypes and protection devices interfaced with the electric machine model on a real-time simulator in a non-destructive environment particularly when faults are studied. A compromise between the model accuracy and computational burden makes the magnetic equivalent circuit (MEC) model ideal for real-time simulation of electric machines. However, satisfying the timing constraints of real-time simulation to accommodate internal machine faults is still challenging due to the nonlinearity and rotation of electric machines. In this paper, the transmission line modeling (TLM) method is utilized to keep the MEC coefficient matrix unchanged during nonlinear iterations. Afterward, for the first time, the entire potential of the TLM method for pre-calculation is exploited by proposing an efficient matrix re-ordering combined with the left-looking Gilbert–Peierls algorithm to minimize the computational burden of the sparse MEC matrix LU decomposition required in each time-step due to rotation. Furthermore, the massive hardware architecture of the field programmable gate array is used as the platform for implementation to fully exploit parallelism. With the proposed MEC-based real-time TLM method, the minimum time-step as low as 500 $\mu \text{s}$ can be achieved and the results validation with two-dimensional finite element model (FEM) of the commercial Jmag-Designer software shows the accuracy and efficiency of the proposed methodology.