Fast Transient Analysis Research Articles

Emergency control methods for power systems based on improved deep reinforcement learning

Abstract In order to achieve fast and accurate transient stability analysis and emergency control, this paper proposes a transient stability emergency control method based on improved deep reinforcement learning. In order to fully explore the temporal and spatial variation trend of transient response, a multi-dimensional feature containing information such as transient situation energy is constructed, and the deep reinforcement learning model is transformed based on the time-space graph neural network. On this basis, an emergency control model is constructed, and the power grid knowledge is integrated into the emergency control decision-making scheme to reduce the exploration of invalid decision-making and improve the performance of the model. The effectiveness of the proposed method is verified in the IEEE-39 system.

Space Division and WGAN-GP Based Fast Generation Method of Practical Dynamic Security Region Boundary

Fast and accurate transient stability analysis is crucial to power system operation. With high penetration level of wind power resources, practical dynamic security region (PDSR) with hyper plane expression has outstanding advantages in situational awareness and series of optimization problems. The precondition of obtaining accurate PDSR boundary is to locate sufficient points around the boundary (critical points). Therefore, this paper proposes a space division and Wasserstein generative adversarial network with gradient penalty (WGAN-GP) based fast generation method of PDSR boundary. First, the typical differential topological characterizations of dynamic security region (DSR) provide strong theoretical foundation that the interior of DSR is hole-free and the boundaries of DSR are tight and knot-free. Then, the space division method is proposed to calculate critical operation area where the PDSR boundary is located, tremendously compressing the search space to locate critical points and improving the confidence level of boundary fitting result. Furthermore, the WGAN-GP model is utilized to fast obtain large number of critical points based on learning the data distribution of the small training set aforementioned. Finally, the PDSR boundary with hyperplanes is fitted by the least square method. The case study is tested on the Institute of Electrical and Electronics Engineers (IEEE) 39-bus system and the results verify the accuracy and efficiency of the proposed method.

Fast and Accurate Transient Analysis of Thin-Wire Structure in Half-Space With PEEC Method

This article presents an efficient full-wave partial element equivalent circuit (PEEC) method of thin-wire structure in half-space for lightning transient analysis. In the framework of the PEEC formulation for thin-wire conductors, the partial elements are computed by double-folded line integrals. In layered media, the interaction integrals involve dyadic Green's functions, which contain a closed-form part and a Sommerfeld-integral part. The direct numerical computation of these integrals is very challenging and time-consuming, which hinders the practical application of the full-wave method. However, the efficient and accurate evaluation of partial elements has not been investigated in a comprehensive way so far. Accordingly, this article presents an efficient method for the evaluation of the partial elements between elementary segments in half space. The main novelty is that the interaction integrals are computed through a combination of the Taylor series expansion of the full-wave free space Green's function and the Sommerfeld-integral adaptive interpolation technique, which significantly reduces the computation time. The new method is systematically validated on examples from finite-difference time-domain (FDTD) method and method of moments and experimental results. The proposed method is validated with the NEC code in the frequency domain and the FDTD in the time domain.

Stimulative Effects of Lupinus sp. and Melilotus albus Underseed on the Photosynthetic Performance of Maize (Zea mays) in Two Intercropping Systems

In order to evaluate influential mechanisms for photosynthetic processes on the yields of an intercropping system composed of maize (Zea mays), Lupinus sp. and Melilotus albus, three treatments were designed and conducted in southern Moravia (Czech Republic) in the form of agronomy trials. The treatments included sole maize (SM), maize with Lupinus sp. (ML) and maize with field melilot (MM). The photosynthetic processes of Zea mays were monitored using several chlorophyll fluorescence techniques on the three treatments for 20 days in the late summer season. An analysis of fast chlorophyll fluorescence transients (OJIP) showed that the capacity of photochemical photosynthetic reactions in photosystem II (FV/FM), as well as the photosynthetic electron transport rate (ET0/RC), declined in response to a four-day episode of extremely warm days with full sunshine. Similarly, the performance index (PI), an indicator of general plant vitality, declined. The episode activated protective mechanisms in photosystem II (PSII), which resulted in an increase of thermal dissipation. For the majority of Z. mays photosynthetic parameters, their values decreased for particular treatments in the following order: MM, ML, SM. The MM and ML intercropping systems had a positive effect on the primary photosynthetic parameters in Z. mays.

ESPSim: An Efficient Scalable Power Grid Simulator Based on Parallel Algebraic Multigrid

Fast verification for the extremely large-scale power grid is demanding as CMOS technology advances consistently. In this work, we propose ESPSim, an efficient scalable power grid simulator based on a parallel smoothed aggregation-based algebraic multigrid technique. ESPSim has the ability to do fast DC and transient analysis through MPI and adaptive timestep control mechanism. Thanks to the smoother applied on the prolongation operator, ESPSim copes well with the convergence rate on extremely large-scale power grid transient analysis. Extensive experiments are conducted with a variety of serial/parallel solvers. The runtime of ESPSim is linear with case size. With 16 processors, 1,000 timesteps transient analysis of 63.4M nodes can be completed in 22.1 min. Over 22× speedup compared to the well-known direct solver Cholmod is observed.

(Invited, Digital Presentation) ML-Based Fast on-Chip Transient Thermal Simulation for Heterogeneous 2.5D/3D IC Designs

Large 3DIC designs with multiple chips requireseveral iterations of transient thermal analysis particularly forfine-grain on-chip dynamic thermal management. This requiresa fast thermal analysis technology as opposed to traditionalCFD/FEA based methods which have severe runtime/capacitylimitations for large chips (e.g., 2cmx2cm) in 3DIC whilegenerating fine grained (e.g., 10umx10um) transient thermalresponse. The fast transient thermal analysis is based on the ideaof combining the global, intermediate, and local transientresponse curves generated from an ML-predictor. The local,intermediate, and global transient response curves are scaledbased on the far-field and near-field transient decay surfacecomponents respectively, computed using the trained ML decaysurface predictor, followed by linear superposition of the curvesfor each power value in the transient power profile to generatethe effective transient response curve. The runtime forgenerating thermal results for a large chip is in the order ofminutes, compared to several hours/days while using CFD/FEAbased tools with good accuracy correlation. The fast transientthermal solver is implemented on distributed ML computingplatform for parallel computation of transient thermal inferencemodel.

Germany's supreme court rules in Solvay's favour on patent case with Neo

Methanol has been shown to promote the hydrocarbon selective catalytic reduction of NOx with octane and toluene over 2 wt% Ag/Al2O3 catalyst for the first time. In order to understand its role in the reaction fast transient kinetic methods and in situ DRIFTS analysis have been used. The catalytic activity tests showed that the addition of methanol to the HC-SCR reaction results in a significant improvement in the low temperature activity of a Ag/Al2O3 catalyst, despite the fact that methanol on its own is not reactive for the HC-SCR reaction. This promotional effect of methanol is dependent on the concentration of added methanol and is not necessarily associated with a higher concentration of reductant in the SCR feed. The fast transient kinetic analysis has shown that at each temperature the addition of methanol enhances the conversions of both NOx and octane and the production of N2 with high selectivity in comparison with those observed with n-octane or toluene alone. This phenomenon is similar to the effect of H2 which may be associated with the release of hydrogen and ammonia during the transient switches at 250 and 300 °C. Together with the fast transient experiments, the DRIFTS results showed that NCO species are formed when introducing methanol to the n-octane-SCR feed while CN species are removed/consumed from the surfaces of the Ag catalyst. These NCO species formed by adding methanol may play a vital role in promoting the catalytic activity of NOx reduction and methanol itself can be an in situ source for hydrogen formation, which subsequently enhances the SCR reaction.

Transient analysis of graphene-based on-chip interconnects using closed-form MRA model

As interconnects in very-large-scale-integration technology shrinks into the sub-22 nm regime, carbon nanotubes, graphene nanoribbons (GNRs), and Cu-GNRs are emerging as potential replacements for conventional copper on-chip interconnects. This paper presents an matrix-rational-approximation (MRA) model for the fast transient analysis of graphene-based on-chip interconnects. The proposed model’s key feature is that it allows the mathematical representation of the transfer function matrix of on-chip graphene-based interconnect networks in the frequency-domain using closed-form rational functions. The network’s rational functions coefficients are derived from per-unit-length parameters and predetermined coefficients of the Padé approximation. The graphene-based network’s time-domain model is directly obtained from the rational function frequency-domain model without any numerical integration techniques. This makes the proposed MRA model more numerically efficient than conventional simulation program with integrated circuit emphasis (SPICE) models. The results obtained using the proposed model show less than 1% error when compared with HSPICE simulations, ensuring the proposed model’s excellent accuracy. A wide eye-height of 0.8137 V and eye-width of 219.87 ps are obtained for the eye-diagram analysis of multilayer graphene nanoribbon lines at 4 Gbps.

NONLINEAR DISTORTION AND NOISE ANALYSIS OF GENERAL GM-C FILTERS

Systems such as Gm-C filters are ideally designed to exhibit linear characteristics. However, their components – especially transconductors – are intrinsically nonlinear. Although there exist many approaches that aim at reducing nonlinear effects while dealing with practical design problems, nonlinear distortion cannot be canceled out completely. Thus, it is important to estimate a degradation of filter performance caused by nonlinearities. In this paper we propose a simple and general method to perform a transient analysis of any Gm-C filter structure based on a matrix description and macro-modeling of transconductors. An analytical description of general Gm-C filters with nonlinear transconductors is introduced. A differential system that determines dynamics of a general structure of Gm-C filter is formulated. This allows us to carry out an effective and fast transient analysis of any Gm-C filter using standard numerical methods. The approach can be applied to investigate any non-linear effects in filters. The noise analysis of Gm-C filters in general setting is also presented. The accuracy of the proposed methods is confirmed by comparison with SPICE simulation. Example of application for performance optimization of 4th order Chebyshev filter is given.

Impact Analysis of Electrical Fast Transients on FlexRay In-Vehicle Networks

Distributed vehicular control systems are responsible for safety-critical applications, depending on communication protocols. In this context, the FlexRay protocol is frequently applied for electronic control unit interconnection in critical applications. Thus, it must be tested in different fault scenarios to verify if the protocol could comply with hard timing constraints. Typical faults that have been studied are electrical fast transients, in which power switching systems can generate transients that degrade in-vehicle communication. Recent efforts focus on the specification of test methods for electromagnetic compatibility in communication transceivers, but without considering the negative impact on critical control system messages and its periodicity. This work presents a contribution by exploring the IEC 62228-3:2019 standard to guide the application of a test method with a specific test board to evaluate the impact of these faults on the control law performance of critical automotive control systems based on FlexRay protocol. The results show that during the test scenarios using the fault injection method, the transients cause performance degradation peaks between 2.9 and 94.5 μs, much higher compared to a typical FlexRay delay. The results emphasize that critical control systems must be stressed with consistent tests to map fault behaviors, observing the operation limit under faults.

Fast and Accurate Transient Analysis of Large Grounding Systems in Multilayer Soil

One of the most accurate approaches to the lightning-related transient analysis of grounding systems in layered soil is based on the method of moments solution of the integral form of the Maxwell equations. The practical application of this rigorous model to large systems is hindered by a great amount of computer time required for the numerical integration of oscillatory and slowly convergent Sommerfeld integrals (SI). As a result, approximate methods that avoid the solution of SI, e.g., image theory-based methods, are often used for computation of the response of large grounding systems. In this article, we extend the application of the rigorous model for large grounding systems in multilayered soil by applying a procedure that minimizes the number of direct computations of the SI using interpolation over a grid of a small number of sample points. We implement a three-dimensional interpolation scheme that adapts to the problem to minimize the interpolation grid, maintaining the accuracy of the rigorous approach. The developed model is applied for the analysis of transient voltages that might couple to secondary cables and disrupt the operation of connected equipment in case of lightning. The analysis shows that there are cases when the image theory-based models might underestimate the possibly harmful transient voltages.

Interaction of a dam-break wave with an obstacle over an erodible floodplain

Abstract Because of climate change, flood-prone areas are more and more frequently exposed to potential casualties and damage. The capability of the flow to carry relevant quantities of sediments during these critical events adds to the further complexity of the resulting scenarios. The interaction between the flow and the obstacles in flood-inundated areas contributes to an increase in the hazard level and constitutes a relevant concern in the framework of risk analysis. Despite this relevance, the existing literature on the topic is relatively scarce, especially for the estimation of the forces acting on rigid obstacles in the presence of a mobile bed. In the present paper, a recent two-phase shallow-water morphodynamical model, particularly suited for the analysis of fast geomorphic transients, is applied for the numerical simulation of the propagation of a dam-break wave over an erodible floodplain in the presence of a rigid obstacle. The geometry of the test-case is inspired by a recent fixed-bed study reported in the literature, for which extensive experimental and numerical data concerning the flow field and the dynamic loading against the obstacle are available. Results of the numerical simulations contribute to highlight the effects of the obstacle on the changes in the bottom topography.

Delayed fission energy effect on LWR normal operation and transients

In reactor core analysis, equilibrium delayed fission energy is often assumed except for estimating the decay heat during reactor shutdown or post-accident scenarios. In this paper, we investigated a few slow and fast transient operational conditions in which the assumption of equilibrium delayed energy could be questionable. A model of lumping the delayed heat source into groups has been adopted in this study to calculate the time-dependent delayed power in the CASL neutronics code MPACT. For the normal operational depletion, the time-integrated effect of the delayed heat shows a small impact in calculating the flux normalization factor, and thus eigenvalue and depletion isotopics. The effect of delayed energy for the reactivity-initiated accident (RIA) problems is more interesting. For a PWR 3-D full core simulation of rod ejection, the peak core power is reduced by about 3% and the decay heat is significantly higher after SCRAM, with an overall energy release increased by 7%. Therefore, the time-dependent delayed model is more beneficial for fast transient analysis. In addition to the temporal effect, the spatial distribution of energy deposited from delayed gamma rays are compared with that from prompt gamma rays for a few typical LWR mini-lattices, and the results affirm that using the scaling approach for spatial energy deposition of delayed gamma rays has good accuracy.

Can malaria rapid diagnostic tests by drug sellers under field conditions classify children 5\xa0years old or less with or without Plasmodium falciparum malaria? Comparison with nested PCR analysis

BackgroundMalaria rapid diagnostic tests (RDTs) available as dipsticks or strips, are simple to perform, easily interpretable and do not require electricity nor infrastructural investment. Correct interpretation of and compliance with the RDT results is a challenge to drug sellers. Thus, drug seller interpretation of RDT strips was compared with laboratory scientist re-reading, and PCR analysis of Plasmodium DNA extracted from RDT nitrocellulose strips and fast transient analysis (FTA) cards. Malaria RDT cassettes were also assessed as a potential source of Plasmodium DNA.MethodsA total of 212 children aged between 2 and 60 months, 199 of whom had complete records at two study drug shops in south western Uganda participated in the study. Duplicate 5 μL samples of capillary blood were picked from the 212 children, dispensed onto the sample well of the CareStart™ Pf-HRP2 RDT cassette and a FTA, Whatman™ 3MM filter paper in parallel. The RDT strip was interpreted by the drug seller within 15–20 min, visually re-read centrally by laboratory scientist and from it; Plasmodium DNA was recovered and detected by PCR, and compared with FTA recovered P. falciparum DNA PCR detection.ResultsMalaria positive samples were 62/199 (31.2%, 95% CI 24.9, 38.3) by drug seller interpretation of RDT strip, 59/212 (27.8%, 95% CI 22.2, 34.3) by laboratory scientist, 55/212 (25.9%, 95% CI 20.0, 32.6) by RDT nitrocellulose strip PCR and 64/212 (30.2%, 95% CI 24.4, 37.7). The overall agreement between the drug seller interpretation and laboratory scientist re-reading of the RDT strip was 93.0% with kappa value of 0.84 (95% CI 0.75, 0.92). The drug seller compliance with the reported RDT results was 92.5%. The performance of the three diagnostic strategies compared with FTA-PCR as the gold standard had sensitivity between 76.6 and 86.9%, specificity above 90%, positive predictive values ranging from 79.0 to 89.8% and negative predictive values above 90%.ConclusionDrug sellers can use RDTs in field conditions and achieve acceptable accuracy for malaria diagnosis, and they comply with the RDT results. Plasmodium DNA can be recovered from RDT nitrocellulose strips even in the context of drug shops. Future malaria surveillance and diagnostic quality control studies with RDT cassette as a source of Plasmodium DNA are recommended.

Optimization of the Transient Feature Analysis for Graphene Chemical Vapor Sensors: A Comprehensive Study

Graphene is very attractive for chemical vapor sensor applications due to its atomically thin structure and unique electronic properties. In this paper, a comprehensive study of transient feature analysis is carried out to optimize the discrimination capability of graphene chemical vapor sensors. Three new transient feature models, enhanced exponential fitting, logarithmic linear fitting and piecewise linear fitting, have been proposed and optimized for precise discrimination against different chemical vapors. Compared with the conventional peak-to-peak method, these three new fitting algorithms significantly improved the prediction accuracy. Among them, the enhanced exponential fitting algorithm reaches the highest prediction accuracy of 92%, about 25% better than the conventional method. Although logarithmic and piecewise models exhibit slightly lower accuracy, they are much simpler and faster in computation than the exponential models. In the application of Internet of Things involving large number of sensors and sensor networks, a fast and accurate transient feature analysis is very important. This paper described a new route in achieving high-performance sensor technologies.

Efficient Computational Fluid Dynamics Model for Transient Laminar Flow Modeling: Pressure Wave Propagation and Velocity Profile Changes

In this paper, the analysis of fast laminar transients in pressurized pipes is developed using a computational fluid dynamics (CFD) model, combined with the Zielke model and laboratory data. The systematic verification of the performance of the CFD model executed in the first part of the paper allows defining the most efficient set of the discretization parameters capable of capturing the main features of the examined transient. In this framework, the crucial role of radial discretization is pointed out. In the second part of the paper, the refined and efficient CFD model is used to examine some aspects of interest for understanding the dynamics of transients. Specifically, the uniformity of the instantaneous pressure distributions along the pipe radius, which validates the results of the most popular quasi-two-dimensional (2D) models, has been revealed. Moreover, it has been shown that the strongest link between the wall shear stress and the axial component of the velocity occurs in the region close to the pipe wall as well as that the time-shift between the wall shear stress and the local instantaneous flow acceleration increases significantly as time elapses.

PEEC-Based Analysis of Complex Fusion Magnets During Fast Voltage Transients With H-Matrix Compression

PEEC-based methodology appears very attractive for the analysis of fast voltage transients which may appear across and inside magnets in fusion devices in case of off-normal events. In this paper, we aim at illustrating how Adaptive Cross Approximation coupled with hierarchical matrix (H-matrix) arithmetics can provide an effective method to allow the solution of large scale problems typical of real devices.

Average value model of grid side converter in PMSG for system‐level studies

In recent years, the subsynchronous oscillation phenomena have been observed in the permanent magnet synchronous generator (PMSG) based wind farms. Therefore, to design an accurate and efficient model for PMSG wind generator becomes an important issue for related stability studies. In this study, an average value model (AVM) for the grid side converter of PMSG is proposed, which can be easily implemented in traditional electromagnetic transients simulation programme. The proposed AVM model consists of an optional DC–DC boost converter, a crowbar protection circuit, and a DC–AC voltage source inverter. Numerical tests are performed for both the AVM and the detailed PMSG model on PSCAD with different scenarios, including both the slow transients studies and fast transient fault analysis. Simulation results of the proposed average value model show good consistency with those of the detailed PMSG model while providing significant speedups. Such characteristics indicate that the proposed model is accurate and efficient for system-level dynamic research.

Voltage‐in‐current formulation for the latency insertion method for improved stability

A new formulation for the latency insertion method (LIM) by implicitly substituting the voltages in the currents is presented. LIM is a fast transient analysis technique for large networks. However, due to its explicit formulation, it has a limitation on the time step size to guarantee numerical stability, similar to the finite-difference time-domain technique. This limits the efficiency of the method particularly where small parasitic inductances and capacitances are present which necessitates the use of very small time steps. Using the new formulation, an improved LIM is presented, where accurate and stable results can be obtained without limitation on the time step size.

Multi-Rate Locally Implicit Block Leapfrog Scheme for Fast Transient Analysis of Multi-Layered Power/Ground Planes

This letter describes the multi-rate locally implicit block leapfrog scheme (LIBLS) for the fast transient analysis of multi-layered power/ground planes. LIBLS is the numerical method constructed by applying a locally implicit scheme to the existing scheme, which is based on an explicit leapfrog scheme. The proposed method improves LIBLS with introducing a multi-rate technique in the time domain, and using different time step sizes for a variety of sub-circuits, and is applicable to the multi-layered network with many coupling elements.