489 research outputs found

    Generalized Voltage-based State-Space Modelling of Modular Multilevel Converters with Constant Equilibrium in Steady-State

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    This paper demonstrates that the sum and difference of the upper and lower arm voltages are suitable variables for deriving a generalized state-space model of an MMC which settles at a constant equilibrium in steady-state operation, while including the internal voltage and current dynamics. The presented modelling approach allows for separating the multiple frequency components appearing within the MMC as a first step of the model derivation, to avoid variables containing multiple frequency components in steady-state. On this basis, it is shown that Park transformations at three different frequencies (+ω+\omega, 2ω-2\omega and +3ω+3\omega) can be applied for deriving a model formulation where all state-variables will settle at constant values in steady-state, corresponding to an equilibrium point of the model. The resulting model is accurately capturing the internal current and voltage dynamics of a three-phase MMC, independently from how the control system is implemented. The main advantage of this model formulation is that it can be linearised, allowing for eigenvalue-based analysis of the MMC dynamics. Furthermore, the model can be utilized for control system design by multi-variable methods requiring any stable equilibrium to be defined by a fixed operating point. Time-domain simulations in comparison to an established average model of the MMC, as well as results from a detailed simulation model of an MMC with 400 sub-modules per arm, are presented as verification of the validity and accuracy of the developed model

    Global Tracking Passivity--based PI Control of Bilinear Systems and its Application to the Boost and Modular Multilevel Converters

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    This paper deals with the problem of trajectory tracking of a class of bilinear systems with time--varying measurable disturbance. A set of matrices {A,B_i} has been identified, via a linear matrix inequality, for which it is possible to ensure global tracking of (admissible, differentiable) trajectories with a simple linear time--varying PI controller. Instrumental to establish the result is the construction of an output signal with respect to which the incremental model is passive. The result is applied to the boost and the modular multilevel converter for which experimental results are given.Comment: 9 pages, 10 figure

    Distributed Control and Optimization of DC Microgrids: A Port-Hamiltonian Approach

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    This article proposes a distributed secondary control scheme that drives a dc microgrid to an equilibrium point where the generators share optimal currents, and their voltages have a weighted average of nominal value. The scheme does not rely on the electric system topology nor its specifications; it guarantees plug-and-play design and functionality of the generators. First, the incremental model of the microgrid system with constant impedance, current, and power devices is shown to admit a port-Hamiltonian (pH) representation, and its passive output is determined. The economic dispatch problem is then solved by the Lagrange multipliers method; the Karush-Kuhn-Tucker conditions and weighted average formation of voltages are then formulated as the control objectives. We propose a control scheme that is based on the Control by Interconnection design philosophy, where the consensus-based controller is viewed as a virtual pH system to be interconnected with the physical one. We prove the regional asymptotic stability of the closed-loop system using Lyapunov and LaSalle theorems. Equilibrium analysis is also conducted based on the concepts of graph theory and economic dispatch. Finally, the effectiveness of the presented scheme for different case studies is validated with a test microgrid system, simulated in both MATLAB/Simulink and OPAL-RT environments

    Operation of a mudular multilevel converter controlled as a Virtual synchronous machine

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    Does ozonation enhance activated carbon adsorption of PFAS in textile wastewater?

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    Per- and polyfluoroalkyl substances (PFAS) are used in numerous industrial applications, such as in textile manufacturing, because of their special chemical properties. To avoid PFAS spread in the environment, removal strategies need to be implemented at the wastewater treatment plants (WWTP) to reduce their environmental risk on receiving water bodies. The fate of 14 PFAS in a full-scale WWTP treating textile and civil wastewater (WW) was investigated. The addition of an adsorption step before or after the ozonation process was studied through adsorption isotherms tested on the WW collected before and after the full-scale ozonation step. Ozonation is not aimed at PFAS removing, but it lowers organic matter competition towards long-chain PFAS in the following adsorption step. The removal of UVA254 seems to be a good proxy variable for PFAS adsorption, with relationships not dependent on the presence of ozonation step

    Mononucleosis infecciosa : Consideraciones etiológicas y de laboratorio

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    Actualmente existe criterio formado para .considerar a la mononucleosis infecciosa como una “enfermedad infecciosa aguda, probablemente de etiología viral, de aparición esporádica en adolescentes v adultos jóvenes, de curso generalmente benigno (autodelimitado), con un peculiar cuadro hemalológico y serológico y manifestaciones clínicas estereotipadas”. Poco queda, por tanto, de la “fiebre glandular” descripta por Pfeiffer en 1889 y caracterizada por ser una enfermedad febril aguda, benigna, contagiosa y epidémica, que atacaba preferentemente a los niños, con adenopatías, pero poca faringitis y linfocitosis inconstante, con frecuente hepatoesplenomegalia y dolores abdominales. Pero, como el mismo Pfeiffer señaló, bajo la designación de fiebre glandular se podían diagnosticar diversos procesos, ya que no se trataría de una entidad nosológica única; v, efectivamente, no habiendo un criterio diagnóstico distintivo, se incluyó bajo esa denominación a un fárrago de infecciones virales v bacterianas. Dos designaciones merecen ser comentadas por la confusión que han ocasionado: en primer lugar, la introducción por Comby en Francia (1894) del término “fiebre ganglionar” para describir cualquier adenopatía secundaría a una infección local; v, en segundo limar, la denominación empicada por Schultz en Alemania (1922) de “angina monocítica” dando lugar al equívoco de creer que es una característica de la mononucleosis infecciosa la presencia de monocitosis, cuando los elementos mononucleares peculiares de esta enfermedad son elementos linfoideos.Facultad de Ciencias Médica

    Comportamiento electrocinético de los minerales de arcilla

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    El estudio y la experimentación previa a la investigación orgánica de la estabilización y drenaje eléctrico de suelos, realizados en el LEMIT durante el período 1947-48 con el asesoramiento del señor Celestino L. Ruiz, Dr.en Qca., y basados en trabajos similares de Rzhanitzie en Rusia y Casagrande y otros en Alemania y Gran Bretaña, demostraron la necesidad de fundamentar los ensayos en una sólida experiencia y cuidadoso conocimiento de la estructura eléctrica y comportamiento electrocinético de la fracción coloidal del suelo, la más importante para el problema en estudio. Por sus propiedades particulares, la fracción arcillosa concentró entonces» toda la atención en cuanto a la aplicación electrocinética. Si bien en la literatura científica se encontraron abundantes datos de la variación del potencial electrocinético de las arcillas con la naturaleza del ión adsorbido, no se encontraron valores comparados del potencial electrocinético de los distintos minerales de arcilla. Radicada la discusión en el campo de la especulación científica, el autor planteó la posibilidad de que los distintos minerales de arcilla diesen valores diferenciales y aún distintivos de potencial zeta. Esta hipótesis so basaba desde el punto de vista práctico en la estabilidad eléctrica distinta de los minerales en suspensión, aún teniendo en cuenta su granulometría particular. Desde el punto de vista teórico se asociaron más tarde las razones que determinan las diferentes capacidades de cambio de las arcillas como determinantes del origen de la doble capa en la superficie de los minerales de arcilla.Al momento de presentación de esta tesis, la actual Facultad de Ciencias Exactas se denominaba Facultad de Química y Farmacia.Tesis digitalizada en SEDICI gracias a la Biblioteca Central de la Facultad de Ciencias Exactas (UNLP).Facultad de Ciencias Exacta

    Graph Neural Stochastic Differential Equations

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    We present a novel model Graph Neural Stochastic Differential Equations (Graph Neural SDEs). This technique enhances the Graph Neural Ordinary Differential Equations (Graph Neural ODEs) by embedding randomness into data representation using Brownian motion. This inclusion allows for the assessment of prediction uncertainty, a crucial aspect frequently missed in current models. In our framework, we spotlight the \textit{Latent Graph Neural SDE} variant, demonstrating its effectiveness. Through empirical studies, we find that Latent Graph Neural SDEs surpass conventional models like Graph Convolutional Networks and Graph Neural ODEs, especially in confidence prediction, making them superior in handling out-of-distribution detection across both static and spatio-temporal contexts.Comment: 9 main pages, 6 of appendix (15 in total), submitted for the Learning on Graph (LoG) conferenc

    La enseñanza de Anatomía en la universidad en tiempos de coronavirus: educación de emergencia – Segunda entrega

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    En esta entrega retomamos lo dicho en el artículo anterior La enseñanza de Anatomía en la universidad en tiempos de coronavirus: educación de emergencia – Parte 1, esta vez para narrar algunas de las estrategias que tuvimos que implementar en nuestra Cátedra, ante la interrupción de la presencialidad en las clases prácticas.Facultad de Humanidades y Ciencias de la Educació

    PID passivity-based droop control of power converters:Large-signal stability, robustness and performance

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    We present a full review of PID passivity-based controllers (PBC) applied to power electronic converters, discussing limitations, unprecedented merits and potential improvements in terms of large-signal stability, robustness and performance. We provide four main contributions. The nominal case is first considered and it is shown—under the assumption of perfect knowledge of the system parameters—that the PID-PBC is able to guarantee global exponential stability of a desired operating point for any positive gains. Second, we analyze robustness of the controller to parameters uncertainty for a specific class of power converters, by establishing precise stability margins. Third, we propose a modification of the controller by introducing a leakage, in order to overcome some of the intrinsic performance and robustness limitations. Interestingly, such controller can be interpreted at steady-state as a droop between the input and the passive output, similar to traditional primary controllers. Fourth, we robustify the design against saturation of the control input via an appropriate monotone transformation of the controller. The obtained results are thoroughly discussed and validated by simulations on two relevant power applications: a DC/DC boost converter and an HVDC grid-connected voltage source converter
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