Fast Time-domain Simulation Research Articles

Reduced-order model for ship motions incorporating a volume-based calculation of body-nonlinear hydrostatic and Froude-Krylov forces

The theoretical background of a fast time-domain simulation tool for ship motion in waves, commonly referred to as SimpleCode, is reviewed. The tool implements a body-nonlinear formulation for the hydrostatic and Froude-Krylov forces with the instantaneous submerged volume and centroid of sections along the ship's length. Other forces are approximated by ODE (ordinary differential equation) like polynomials. SimpleCode implements a six degrees of freedom (DOF) solver as well two 3-DOF solvers: one for vertical plane motions (heave, roll, and pitch) and another for horizontal plane motions (surge, sway, and yaw). While the initial objective of the tool was limited to the statistical validation of extrapolation methods, it was later extended to other applications and is considered to be a general reduced-order numerical model (ROM) of ship motions in waves. The SimpleCode has been used for the development and statistical validation of the EPOT and split-time methods and for the identification of extreme response events in a multi-fidelity seakeeping analysis.

Fast Response Prediction Method Based on Bidirectional Long Short-Term Memory for High-Speed Links

There is a recognized need to evaluate the performance of high-speed links accurately and quickly with increasing clock frequency. To evaluate the performance of the systems, the transient simulation method and the fast time-domain simulation method are adopted. Unfortunately, neither method can guarantee both the efficiency and accuracy of the results at the same time. In this article, a modeling method that can overcome the shortcomings of both the transient simulation method and the fast time-domain simulation method is proposed for obtaining responses of high-speed links based on bidirectional long short-term memory (Bi-LSTM). Here, the pulse response and response of a certain number of bits are first simulated or measured, which are used to determine training datasets. Then, the Bi-LSTM-based model uses the generated training datasets to build a precise model. Next, the developed model predicts the response of the high-speed link. Compared to the transient simulation method and fast time-domain simulation method, the results show that the proposed method can consider both accuracy and efficiency. In addition, 33 simulation experiments are performed to demonstrate the robustness of the proposed method. Finally, the accuracy of the proposed method is validated by comparing the measured and predicted results of the high-speed links with different nonlinearities.

A fully coupled frequency domain model for floating offshore wind turbines

This paper presents a new frequency domain modeling approach for floating offshore wind turbines with coupled wind turbine, floating platform, and mooring system sub-models. The sub-models are generated using the validated numerical tools FAST and WAMIT to obtain the frequency domain aerodynamic and hydrodynamic characteristics, respectively, for any given design candidate. The turbulent wind and irregular wave loads are incorporated in the frequency domain model using wind and wave power spectral density functions, the JONSWAP and Kaimal spectra, respectively. To validate the proposed 6 DOF frequency domain framework across standard operational environmental conditions, predicted system responses of a 5 MW NREL offshore wind turbine with three classes of reference platforms including the OC3-Hywind, the MIT/NREL TLP, and the OC4-DeepCwind semisubmersible were compared to the outputs of 6 DOF and 22 DOF FAST time domain simulations. The comparison over an aggregate of eleven environmental conditions focused on differences in predicted platform rigid body motions and structural considerations including platform surge, roll, and pitch, and rotor thrust, total blade root and tower base bending moments/fatigue loads, fairlead and anchor tensions/fatigue loads. In terms of platform motions, the worst match of frequency and time domain model predictions was seen for the OC4-DeepCwind semisubmersible with errors of 13.2% in peak displacement values. The frequency domain model predictions of rotor thrust, blade root and tower base bending moments demonstrated the largest error in the case of the OC3-Hywind spar buoy with the peak loads differing by up to 12.8%. Errors in the predictions of maximum fairlead and anchor tensions were less than 11.5% with maximum error occurring for the MIT/NREL TLP. In terms of fatigue load comparison, the blade root and tower base fatigue load predictions showed less than 9.8% errors for all the reference platforms. Comparison of the fairlead and anchor fatigue loads showed that errors were less than 13.8% with the largest error seen for the OC3-Hywind spar buoy platform. Overall, the frequency domain model provides reliable means for assessing platforms dynamics at the conceptual stage of the design process.

A new calculation technique for onboard progressive flooding simulation

ABSTRACTDuring a flooding emergency, the master has to take hard decisions with serious impact on passengers and crew safety. A fast and reliable time domain simulation of the progressive flooding process can significantly aid the master in choosing the right counteractions immediately after the damage occurrence. In last decades many methods to simulate progressive flooding have been developed with increasing precision, but most of them require too much computational effort being not suitable for a direct onboard application. This paper presents a novel quasi-static simulation technique capable to provide accurate results in a reasonable calculation time. The analytical solution of the linearised system of governing differential equations allows to extend the time step over the intrinsic limits of numerical integration methods without affecting accuracy. The approach has been compared with numerical integration of non-linear system of equations and a recent pressure correction technique on a box-barge test case available in the literature.

Combining induction control and wake steering for wind farm energy and fatigue loads optimisation

Turbine power and yaw set points can be adjusted across a wind farm to minimise the overall power losses and the additional fatigue loads caused by wake interactions. Detailed modelling is required to understand the complex flows in sufficient detail to allow a realistic practical control design. High-fidelity computational fluid dynamics requires enormous computational resources, so simpler engineering models are needed which capture the most important effects while running fast enough to allow sufficient testing. This paper describes a steady-state optimisation tool which has been extended to optimise all the power reduction set-points and yaw offsets simultaneously for different wind conditions. It also describes a fast time-domain simulation model which captures turbine and wake dynamic effects, so that wind farm controllers of all kinds can be tested in realistic and time-varying conditions. To demonstrate its application for controller testing, the performance of the combined power and yaw controller is tested during changing conditions of wind speed, direction and turbulence derived from measured site data. Finally, the need for validation is discussed, as many uncertainties still need to be resolved in order to obtain sufficient confidence that the potential benefits of such wind farm control schemes can be realised in practice.

Fast time domain simulation of power systems using multilevel preconditioners with adaptive reconstruction strategies

Time domain simulation (TDS) is an important tool for the analysis of the dynamic behavior of power systems. TDS is a hard computational problem due to the complexity in solving a sequence of large linear systems based on Jacobian matrices. Iterative solvers with various preconditioning techniques have been applied to solve these systems, and among which GMRES is reported to be the most robust. This paper explores the use of multilevel preconditioning technique based on INDependent SETs (INDSETs) and with fill-in guidance. To reduce the system size more effectively, we propose the use of large supernodes instead of single vertices for INDSET choice. Furthermore, a dynamic preconditioner reconstruction strategy is proposed to incorporate the runtime convergence information of the linear system solving process during the simulation. Experiments show that the proposed multilevel preconditioners have a much lower memory usage and computational overhead than their ILU counterparts. By using supernodes and fill-in guidance, we further reduce the size of the multilevel system and total number of nonzeros by 40% and 13%, respectively. The proposed preconditioner reconstruction strategy shows good adaptivity and performance compared with the strategies based on fixed time intervals.

Teaching Behavioral Modeling and Simulation Techniques for Power Electronics Courses

This paper suggests a pedagogical approach to teaching the subject of behavioral modeling of switch-mode power electronics systems through simulation by general-purpose electronic circuit simulators. The methodology is oriented toward electrical engineering (EE) students at the undergraduate level, enrolled in courses such as “Power Electronics,” “Industrial Electronics,” or the like. The proposed approach is demonstrated by simulation example of a realistic active power factor corrector (APFC) system. The paper discusses the derivation of PSPICE/ORCAD-compatible behavioral models, their software implementation, and fast time domain, frequency domain, and stability analysis simulation techniques suitable for virtual study of complex nonlinear feedback systems. Some “tricks of the trade” are also suggested. The paper can be helpful to instructors of a “Virtual Power Electronics Laboratory” course wanting to conduct a software experiment on a PFC system.

An Approach to Average Modeling and Simulation of Switch-Mode Systems

This paper suggests a pedagogical approach to teaching the subject of average modeling of PWM switch-mode power electronics systems through simulation by general-purpose electronic circuit simulators. The paper discusses the derivation of PSPICE/ORCAD-compatible average models of the switch-mode power stages, their software implementation, and fast time-domain, frequency-domain, and stability analysis simulation techniques suitable for virtual study of complex switch-mode feedback systems. The proposed approach is demonstrated by a simulation example. The methodology is oriented toward Electrical Engineering students at the undergraduate level, enrolled in courses such as “Power Electronics,” “Industrial Electronics,” or the like. The paper can be helpful to instructors of a “Virtual Power Electronics Laboratory” course wanting to conduct a software experiment on dynamics of switch-mode power converter systems. Engineers and scientists approaching the task of simulation of switch-mode systems can also find the suggested technique useful.

The Study of Fast Optimal Generator Shedding Based on Predictor-Corrector Method

This paper presents a fast optimal generator shedding algorithm which is on the basis of predictor-corrector method and time domain simulation for transient stability. It includes two parts that are the fast time domain simulation and optimal generator shedding. On the basis of the generator's classical model and load's constant impedance model, this paper use fourth-order Hamming predictor-correction formula to compute differential equations of the system with large step length, in order to improve computing speed. The second part shows how to calculate the sensitivity of transient stability constraint function to control variables, by the application of optimal control theory. Combined with the discrete characteristics of generator shedding, “Micro-step discrete method” is proposed, which is fast, accurate and so on. The advantages of this method are verified by analysis results of New England 39-bus test system.

A Novel Modal Technique for Time and Frequency Domain Analysis of Waveguide Components

A new modal algorithm for fast frequency or time domain simulation of waveguide components and resonators is proposed. The new algorithm is based on the finite difference frequency domain method combined with domain decomposition, model order reduction and the projection of fields at domain boundaries on a modal basis. As a result, one converts Maxwell's equations into a very compact set of linear equations which can be solved extremely fast, at least two orders of magnitude faster than with previous algorithms and whose coefficient matrix is independent of frequency.

Methods of Interfacing Rotating Machine Models in Transient Simulation Programs

The electromagnetic transient programs (EMTP-like tools) are based on the nodal (or modified nodal) equations that enable an efficient numerical solution and, subsequently, fast time-domain simulations. The state-variable-based simulation programs, such as Simulink, are also used for studying the dynamics of electrical systems. Both the offline and real-time versions of these two types of simulation tools are widely used by the researchers and engineers in industry and academia to study the transient phenomena and dynamics in power systems with rotating electrical machines. This paper provides a summary of the interfacing techniques that are utilized to integrate the general-purpose models of electrical machines with the rest of the power system network for these studies. The interfacing methods are broadly classified as indirect and direct approaches. The paper also describes the numerical properties as well as limitations imposed by the interfacing of the commonly used machine models that should be considered when selecting the simulation parameters and assessing the final results.

Implementation of electrothermal system-level model for RF power amplifiers in Scilab/Scicos environment

This paper presents a behavioral electrothermal model implementation for high RF power amplifiers dedicated to the simulation of radar application in the Scilab/Scicos environment. This model, based on the direct coupling between a behavioral electrical model and a physics-based reduced thermal model, allows to predict nonlinear effects, high-frequency memory effects, and thermal effects due to the amplifier self-heating. System model implementation in Scilab/Scicos platform allows fast time domain simulation with very good convergence properties.

Fast Simulation Technique of Plane Circuits via Two-Layer CNN-Based Modeling

A fast time-domain simulation technique of plane circuits via two-layer Cellular Neural Network (CNN) -based modeling, which is necessary for power/signal integrity evaluation in VLSIs, printed circuit boards, and packages, is presented. Using the new notation expressed by the two-layer CNN, 1,553 times faster simulation is achieved, compared with Berkeley SPICE (ngspice). In CNN community, CNNs are generally simulated by explicit numerical integration such as the forward Euler and Runge-Kutta methods. However, since the two-layer CNN is a stiff circuit, we cannot analyze it by using an explicit numerical integration method. Hence, to analyze the two-layer CNN and reduce the computational cost, the leapfrog method is introduced. This procedure would open an application of CNN to electronic design automation area.

Fast time-domain simulation of optical waveguide structures with a multilevel dynamically adaptive mesh refinement FDTD approach

The finite-difference time-domain (FDTD) technique has been widely employed for the modeling of both linear and nonlinear optical structures. Its main advantages, however, namely, simplicity and versatility, are offered at the expense of significant computational resources needed for the simulation of realistic geometries. In this paper, a recent approach that incorporated an adaptively refined moving mesh into the FDTD technique for microwave circuit design is applied to two-dimensional optical waveguide problems, resulting in dramatic simulation time savings, compared with FDTD, while maintaining its accuracy. To complement the applicability of the proposed technique as a novel photonics design tool, numerical error studies that facilitate the educated a priori choice of the simulation parameters are provided

Compiled code simulation of analog and mixed-signal systems using piecewise linear modeling of nonlinear parameters: A case study for [formula omitted] modulator simulation

This paper presents a methodology for fast time-domain simulation of analog systems with nonlinear parameters. Specifically, the paper focuses on Δ Σ analog-to-digital converters (ADC). The method creates compiled-code simulators based on symbolic analysis. Code is optimized using loop invariant elimination and constant folding, well-known compiler optimization methods. Circuits are described as structural macromodels. Nonlinear parameters are expressed using piecewise linear (PWL) models. The paper presents a technique for automatically creating PWL models through model extraction from trained neural networks. As compared to existing behavioral simulation methods for Δ Σ ADC, this technique is more systematic and accurate. In our experiments, compiled-code simulation was significantly faster than numerical simulation. Hence, the methodology is very useful in analog and mixed-signal system synthesis, which is known to require a large number of simulation steps.

Analytic transient solution of SCFL logic gates

In this paper we propose the analytical solution of switching transients for SCFL logic gates. The analysis of an SCFL logic gate is carried out without linearization and can be brought back to multiple analyses of a basic cell, given by a differential pair with switching input voltages and a variable tail current, to take the effect of series-gating into account. The differential equation for this cell is a Riccati equation, if a quadratic current–voltage relationship is used for the transistors, and it can be solved by the infinite power series method, in case of polynomial input signals. An algorithm is proposed to analyse the full transient of a complex SCFL gate. This provides a closed form expression for transient signals in terms of circuit and device parameters, that can be used for symbolic analysis or fast time-domain numerical simulation. Some case studies are presented for SCFL gates using OMMIC ED02AH technology, and a good agreement between the proposed model and SPICE simulations using complex device models is obtained. Copyright © 2005 John Wiley & Sons, Ltd.

Piecewise-Exponential Approximation for Fast Time-Domain Simulation of 2-D Cellular Neural Networks

Cellular neural networks (CNNs) were introduced as promising image processing systems. However, since analytical design techniques are rarely available, extensive simulation is the main practical tool for developing significant applications. This paper presents a new algorithm for fast simulation of large-scale CNNs. It is based on the discretization of the sigmoid generating the output from the state of each cell. This discretization leads to a piecewise exponential approximation of the time-domain solution. Computation is only required when the output of a cell jumps to a different discrete level and involves only this cell and its neighbors. The algorithm is spatially adaptive since the computational effort is concentrated on the most rapidly evolving portions of the array.

Integrated framework for voltage security assessment

Optimal operation of an electrical system requires complete control of the economic impact of security and raises the question of the accurate estimation of the risks. Therefore, the ability of a utility to achieve these goals in the context of more and more complex power systems will be a major factor of competitiveness. With this in mind, EDF has decided to develop a Voltage Security Assessment tool. This software is based on a fast time domain simulation engine, which has been embedded in EDF grid security analysis framework. Its main features are the simulation of voltage stability phenomena and slow dynamics, the computation of different kinds of security margins, the suggestion and the validation of corrective actions. It is being experimented in the French national control center, where it should be used to prepare the system operation, especially the day before, as well as in the on-line environment.

Fast time-domain simulation by waveform relaxation methods

Fast time-domain simulation of power electronic systems by using waveform-relaxation methods is presented. Algorithms for circuit partitioning, time windowing, and simulation scheduling are developed. Practical implementation of the partitioning algorithm based on modal analysis is also discussed. Feasibility and advantages of applying these methods to power electronic systems are demonstrated by simulation results for a series resonant converter and a boost zero-voltage-transition PWM converter.

Fast simulation of power system dynamics in a general-purpose simulator

The increased complexity of power systems and their related controls requires more and more sophisticated analytic tools. Moreover, actual systems are often managed close to their technical limits. Thus, the functions of security analysis, both static and dynamic, become mandatory. In particular, fast time-domain simulations can be used for dynamic security assessment. This paper presents an effective simulator to investigate, in depth, a wide variety of phenomena that can span from a few tens of ms up to several tens of minutes. The classical time dichotomy among different dynamic phenomena is dealt with, by adopting an original technique based on an automatic switching from detailed models of components to simplified ones and vice versa, according to the dynamic conditions of the system. The performance of the power-system simulator will be pointed out by showing an application to a large-size system.