1,720,999 research outputs found
Isomorphic Circuit Clustering for Fast and Accurate Electromagnetic Transient Simulations of MMCs
No full textModular multilevel converters have become the technology of choice in high voltage direct current systems. They are composed of a large number of submodules, which poses significant computational challenges to electromagnetic transient simulations. To address this issue, scholars proposed several approaches that are a trade-off between simulation accuracy and computational burden, which mainly achieve numerical efficiency by adopting reduced and simplified models of the converter arm submodules. This paper proposes a different simulation paradigm based on sub-circuit isomorphism. It is suited for the analysis of intrinsically modular electronic circuits, as it exploits the common behavior of structurally identical submodules by clustering them together. This method does not require any simplification of the submodule electrical model and minimizes the number of equations to be solved at each time step of the time domain analysis, thereby significantly reducing the computational effort. Thus, this method is suitable for thorough simulations of ac/dc networks, which may require the implementation of detailed transistor-level representations of the converter submodules
BAL: A library for the brute-force analysis of dynamical systems
No full textThis paper describes the functionality and usage of bal, a C/C++ library with a Python front-end for the brute-force analysis of continuous-time dynamical systems described by ordinary differential equations (ODEs). bal provides an easy-to-use wrapper for the efficient numerical integration of ODEs and, by detecting intersections of the trajectory with appropriate Poincaré sections, allows to classify the asymptotic trajectory of a dynamical system for bifurcation analysis. Some examples of application are discussed, concerning two-dimensional bifurcation diagrams, Lyapunov exponents and finite-time Lyapunov exponents, basins of attraction, simulation of switching ODE systems, and integration with AUTO, a software package for continuation analysis.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Modelling the Effects of Early Exposure to Alcohol on the Excitability of Cortical Neurons
No full textIn recent years, a novel approach based on multi-objective optimization has been developed to automatically tune biophysically realistic, multi-compartmental neuron models starting from electrophysiological recordings. Here, we apply this methodology to the optimization of model neurons capable of reproducing the reduced excitability observed in experiments carried out in cortical pyramidal cells in a rodent model of fetal alcohol spectrum disorder. We find that both control and ethanol-exposed model cells present an excellent match with the experiments in terms of membrane voltage dynamics, with the latter group displaying a small but significant rightward shift of their current-frequency relationship. We identify a possible interplay between model parameters and cellular morphology and suggest future improvements to better capture the features of dendritic voltage dynamics
Application of Envelope-Following Techniques to the Shooting Method
Full text linkWe consider circuits driven by two or more signals with very different periods and propose a method to determine their steady state solution in the time domain. We present a new version of the shooting method based on the envelope following technique. We show how to use the envelope following method as the new engine to efficiently determine the trajectory of the circuit starting from the new guess of the initial conditions. It substitutes the less efficient time domain analysis used in the conventional implementation of the shooting method. We show that it is well suited to circuits where the ratio between the periods of the slow and fast behaviour is particularly high and characterised by strong non-linearities. The numerical properties at the basis of the proposed method are presented. Its features are shown by simulating different types of slow-fast circuits
Modular Multilevel Converter Models and Simulation Approaches
No full textThe electromagnetic transient simulation of modular multilevel converters (mmcs) in high voltage direct current (hvdc) systems is a burdensome task due to their high number of nodes and semiconductor devices. To cope with this issue, scholars proposed over the years several mmc models that implement different trade-offs between simulation speed and accuracy. One of the common traits of these representations is that they simplify the model of the semiconductor devices inside the mmc. Other than providing a thorough review and comparison of the most popular mmc models in the literature, this book proposes a novel mmc simulation approach based on sub-circuit isomorphism. This approach, originally conceived to analyse modular electronic circuits such as random access memories, can be profitably exploited to simulate mmcs, since it exploits the common behaviour of structurally identical sub-modules inside them by clustering them together. As a result, the isomorphism-based approach allows performing detailed, yet efficient simulations of hvdc systems
Validation of the Isomorphism-Based Approach
No full textThe purpose of this chapter is to validate the isomorphism-based simulation approach by simulating a benchmark hvdc system made up of two mmcs, as well as two dc underground cables and ac grids. After describing the implementation of each component of the benchmark, the chapter presents the results obtained by simulating the hvdc system in several scenarios (ranging from normal operating conditions to faults in the ac and dc side of the mmcs) with two approaches: conventional and isomorphism-based. Simulation results are compared to showcase the key features of the isomorphism-based method and highlight its applicability for the analysis of mmc-based hvdc systems
A Nonlinear Behavioral Ferrite-Core Inductance Model Able to Reproduce Thermal Transients in Switch-Mode Power Supplies
No full textMore compact Switch-Mode Power Supplies (SMPSs) satisfying typical design specifications can be obtained by exploiting ferrite core inductors working in partial saturation. In this case, the inductance is no longer a constant parameter, since it exhibits a sharp drop as the inductor current increases. A behavioral model was recently proposed, which provides the inductance at steady state as a function of easy-to-measure quantities. Here, a generalization of this model is presented, in order to capture the inductance behavior also during thermal transients. The model fitting to experimental measurements relies on an iterative optimization procedure grounding on accurate SMPS simulations based on shooting analysis. The model validation exploits the envelope analysis method, particularly suitable for slow-fast systems. The obtained fitting results show a good agreement with experimental data both in transient conditions (after sudden variation of the SMPS operating condition) and at steady state. Finally, by partially re-identifying the model based on data measured when the inductor is cooled with a fan, we still obtain a good matching between model and experimental data
Nonlinear behavioural model of charge pump PLLs
No full textDespite the nonlinear nature of even the simplest versions of phase locked loops (PLLs), linear models are still used during the first phases of the design of modern PLLs. Even though the linear model may represent a crude approach, its use is justified by the fact that accurate numerical simulations often require a too large amount of CPU time, being PLLs by construction stiff circuits, characterised by very different time scales.
This aspect has triggered the need for compact models that allow fast and accurate numerical simulations. The scientific literature numbers several models that have been developed with different approaches and tailored to different simulation environments. In this context, we propose a nonlinear model of a type-II PLL, which (1) considers both the switching behaviour of the phase/frequency detector and charge pump and the complex dynamics (including the presence of amplitude and phase noise) of the voltage controlled oscillator, (2) is compact and can be easily implemented in modern mixed analog/digital simulators as a behavioural block, and (3) allows the simulation of spurs owing to the nonlinearities of both the charge pump and the fractional frequency divider
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