Polytechnic University of Catalonia

About: Polytechnic University of Catalonia is a education organization based out in Barcelona, Spain. It is known for research contribution in the topics: Finite element method & Population. The organization has 16006 authors who have published 45325 publications receiving 949306 citations. The organization is also known as: UPC - BarcelonaTECH & Technical University of Catalonia.

Modeling of a variable speed wind turbine with a Permanent Magnet Synchronous Generator

Abstract: The aim of this work is to analyze a typical configuration of a Wind Turbine Generator System (WTGS) equipped with a Variable Speed Generator. Nowadays, doubly-fed induction generators are being widely used on WTGS, although synchronous generators are being extensively utilized too. There are different types of synchronous generators, but the multi-pole Permanent Magnet Synchronous Generator (PMSG) is chosen in order to obtain its model. It offers better performance due to higher efficiency and less maintenance since it does not have rotor current and can be used without a gearbox, which also implies a reduction of the weight of the nacelle and a reduction of costs. Apart from the generator, the analyzed WTGS consists of another three parts: wind speed, wind turbine and drive train. These elements have been modeled and the equations that explain their behavior have been introduced. What is more, the whole WTGS has been implemented in MATLAB/Simulink interface. Moreover, the concept of the Maximum Power Point Tracking (MPPT) has been presented in terms of the adjustment of the generator rotor speed according to instantaneous wind speed.

Hydrogen Bond Dynamics in Water and Ultrafast Infrared Spectroscopy: A Theoretical Study

Abstract: Molecular Dynamics simulations are used to examine several key aspects of recent ultrafast infrared experiments on liquid water dynamics in an amplified and extended version of a recent communication [J. Phys. Chem. A 2002, 106, 11993]. It is found that the relation between the OH stretch frequency and the length of the hydrogen bond in which the OH is involved is characterized by considerable dispersion. This dispersion, which is in part related to the varying OHO angle of the hydrogen bond, precludes a one-to-one correspondence between the OH frequency and the hydrogen bond length. Further, it is found that the time scale currently interpreted in terms of a stochastic modulation by the surrounding solvent of a highly frictionally damped hydrogen bond system is largely governed by hydrogen bond-breaking and -making dynamics, while the motion of an intact hydrogen-bonded complex is underdamped in character. A detailed analysis of these issues is provided for calculated spectral dynamics after creation of ...

Self-organization of collaboration networks.

Abstract: We study collaboration networks in terms of evolving, self-organizing bipartite graph models. We propose a model of a growing network, which combines preferential edge attachment with the bipartite structure, generic for collaboration networks. The model depends exclusively on basic properties of the network, such as the total number of collaborators and acts of collaboration, the mean size of collaborations, etc. The simplest model defined within this framework already allows us to describe many of the main topological characteristics (degree distribution, clustering coefficient, etc.) of one-mode projections of several real collaboration networks, without parameter fitting. We explain the observed dependence of the local clustering on degree and the degree‐degree correlations in terms of the “aging” of collaborators and their physical impossibility to participate in an unlimited number of collaborations.

Fast-Processing Modulation Strategy for the Neutral-Point-Clamped Converter With Total Elimination of Low-Frequency Voltage Oscillations in the Neutral Point

Abstract: This paper presents a novel modulation strategy for a neutral-point-clamped converter. This strategy overcomes one of the main problems of this converter, which is the low-frequency voltage oscillation that appears in the neutral point under some operating conditions. The proposed modulation strategy can completely remove this oscillation for all the operating points and for any kind of loads, even unbalanced and nonlinear loads. The algorithm is based on a carrier-based pulsewidth modulation. Nevertheless, it can generate the maximum output-voltage amplitudes that are attainable under linear modulation, such as space-vector modulation. Furthermore, this technique can be implemented with a very simple algorithm and, hence, can be processed very quickly. The only drawback of this strategy is that the switching frequencies of the devices are one third higher than those of standard sinusoidal pulsewidth modulation. A control loop for balancing the voltages on the dc-link capacitors is also proposed. This balancing strategy is designed, so that it does not further increase the switching frequencies of the devices when it is applied to the converter. The proposed modulation technique is verified by simulation and experiment.