University of Seville

About: University of Seville is a education organization based out in Seville, Andalucía, Spain. It is known for research contribution in the topics: Population & Model predictive control. The organization has 20098 authors who have published 47317 publications receiving 947007 citations. The organization is also known as: Universidad de Sevilla.

Extended State Observer-Based Sliding-Mode Control for Three-Phase Power Converters

Abstract: This paper proposes an extended state observer (ESO) based second-order sliding-mode (SOSM) control for three-phase two-level grid-connected power converters. The proposed control technique forces the input currents to track the desired values, which can indirectly regulate the output voltage while achieving a user-defined power factor. The presented approach has two control loops. A current control loop based on an SOSM and a dc-link voltage regulation loop which consists of an ESO plus SOSM. In this work, the load connected to the dc-link capacitor is considered as an external disturbance. An ESO is used to asymptotically reject this external disturbance. Therefore, its design is considered in the control law derivation to achieve a high performance. Theoretical analysis is given to show the closed-loop behavior of the proposed controller and experimental results are presented to validate the control algorithm under a real power converter prototype.

On spiking neural P systems

Abstract: This work deals with several aspects concerning the formal verification of SN P systems and the computing power of some variants. A methodology based on the information given by the transition diagram associated with an SN P system is presented. The analysis of the diagram cycles codifies invariants formulae which enable us to establish the soundness and completeness of the system with respect to the problem it tries to resolve. We also study the universality of asynchronous and sequential SN P systems and the capability these models have to generate certain classes of languages. Further, by making a slight modification to the standard SN P systems, we introduce a new variant of SN P systems with a special I/O mode, called SN P modules, and study their computing power. It is demonstrated that, as string language acceptors and transducers, SN P modules can simulate several types of computing devices such as finite automata, a-finite transducers, and systolic trellis automata.

Grid-Connected Photovoltaic Generation Plants: Components and Operation

Abstract: The main design objective of photovoltaic (PV) systems has been, for a long time, to extract the maximum power from the PV array and inject it into the ac grid. Therefore, the maximum power point tracking (MPPT) of a uniformly irradiated PV array and the maximization of the conversion efficiency have been the main design issues. However, when the PV plant is connected to the grid, special attention has to be paid to the reliability of the system, the power quality, and the implementation of protection and grid synchronization functions. Modern power plants are required to maximize their energy production, requiring suitable control strategies to solve the problems related to the partial shading phenomena and different orientation of the PV modules toward the sun. Moreover, the new policy concerning the injection of reactive power into the grid makes the development of suitable topologies and control algorithms mandatory. A general view of actual solutions for applications of the PV energy systems is presented. This article covers several important issues, including the most reliable models used for simulation, which are useful in the design of control systems, and the MPPT function, particularly in distributed applications. The main topologies used in the PV power processing system and, finally, grid connection aspects are discussed, with emphasis on synchronization, protections, and integration.

High calcium concentrations shift the mode of exocytosis to the kiss-and-run mechanism.

Abstract: Exocytosis, the fusion of secretory vesicles with the plasma membrane to allow release of the contents of the vesicles into the extracellular environment, and endocytosis, the internalization of these vesicles to allow another round of secretion, are coupled. It is, however, uncertain whether exocytosis and endocytosis are tightly coupled, such that secretory vesicles fuse only transiently with the plasma membrane before being internalized (the 'kiss-and-run' mechanism), or whether endocytosis occurs by an independent process following complete incorporation of the secretory vesicle into the plasma membrane. Here we investigate the fate of single secretory vesicles after fusion with the plasma membrane by measuring capacitance changes and transmitter release in rat chromaffin cells using the cell-attached patch-amperometry technique. We show that raised concentrations of extracellular calcium ions shift the preferred mode of exocytosis to the kiss-and-run mechanism in a calcium-concentration-dependent manner. We propose that, during secretion of neurotransmitters at synapses, the mode of exocytosis is modulated by calcium to attain optimal conditions for coupled exocytosis and endocytosis according to synaptic activity.