Modeling and Control of High-Voltage Direct-Current Transmission Systems: From Theory to Practice and Back

The problem of modeling and control of multi-terminal high-voltage direct-current transmission systems is addressed in this paper, which contains five main contributions. First, to propose a unified, physically motivated, modeling framework - based on port-Hamiltonian representations - of the various network topologies used in this application. Second, to prove that the system can be globally asymptotically stabilized with a decentralized PI control, that exploits its passivity properties. Close connections between the proposed PI and the popular Akagi's PQ instantaneous power method are also established. Third, to reveal the transient performance limitations of the proposed controller that, interestingly, is shown to be intrinsic to PI passivity-based control. Fourth, motivated by the latter, an outer-loop that overcomes the aforementioned limitations is proposed. The performance limitation of the PI, and its drastic improvement using outer-loop controls, are verified via simulations on a three-terminals benchmark example. A final contribution is a novel formulation of the power flow equations for the centralized references calculation

Detection of Broken Bars in Induction Motors Using an Extended Kalman Filter for Rotor Resistance Sensorless Estimation

International audienceThis paper deals with the broken bars detection in induction motors. The hypothesis on which detection is based is that the apparent rotor resistance of an induction motor will increase when a rotor bar breaks. To detect broken bars, measurements of stator voltages and currents are processed by an Extended Kalman Filter for the speed and rotor resistance simultaneous estimation. In particular, rotor resistance is estimated and compared with its nominal value to detect broken bars. In the proposed extended Kalman Filter approach, the state covariance matrix is adequacy weighted leading to a better states estimation dynamic. Its main advantage is the correct rotor resistance estimation even for an unloaded induction motor. As part of this estimation process, it is necessary to compensate for the thermal variation in the rotor resistance. Computer simulations, carried out for a 4-kW four-pole squirrel cage induction motor, provide an encouraging validation of the proposed sensorless broken bars detection technique

Optimisation des Pertes par Commutation dans un Convertisseur Modulaire Multiniveaux (MMC)

International audienceLes pertes dans une liaison à courant continu àhaute tension sont un facteur pénalisant (4000 €/kW sur une duréede 30 ans). L’inconvénient vient des structures de type Onduleurde tension qui ont des pertes élevées (1.8%) relativement auxstructures à base de thyristors. L’arrivée des convertisseurs detype Modulaires Multiniveaux (MMC) a permis de réduire cespertes à 1%. Cet avantage permet d’envisager une forte utilisationde cette structure dans des applications HVDC. Le but de cetravail est d’étudier le contrôle bas niveau de ce convertisseur quicorrespond au choix des sous-modules à utiliser et à l’équilibragedes condensateurs afin de minimiser la fréquence de commutation.En se focalisant sur un contrôle de type ondulation des tensions dessous modules, une amélioration a été apportée via une réductionde la fréquence de commutation moyenne de ces sous-modules. Dessimulations sous MATLAB/Simulink ont été conduites et ontpermis de valider la méthode proposée

CHALLENGES OF TEACHING ARTS AT UNIVERSITY BETWEEN PEDAGOGY AND ANDRAGOGY PLASTIC ARTS AND CINEMA AS A MODEL

This study brings together the paradoxes of educational concepts focused on educating children and those focused on educating adults. It explores the question of variables and constants in the concept of andragogy. Furthermore, it seeks to define andragogy and related and adjacent concepts, taking into account the overlap between them, particularly in terms of their focus on teaching methods for adults, particularly in university settings, where students are not young learners to whom pedagogical concepts apply. This study also addresses the challenges of adult education in the fields of cinema and plastic arts, between university institutions whose primary concern is unconditional intellectual openness, and those whose sole concern is to build individuals and groups within political programs and specific agendas, whose sole concern is to integrate the individual within the collective mind of society or a single group, within the concept of the nation-state

The strategy of developing the domestic tourism sector in Algeria in light of the Corona pandemic

Domestic (internal) tourism is currently considered as an important strategic option, as it is one of the most important sectors contributing to achieving economic and social development goals, as Algeria has natural, cultural, and heritage tourism potentials that make it a tourist destination and a tourist attraction by excellence, and we have relied in our research on the descriptive approach in an attempt to know the strategy followed by the government in order to advance this sector in light of the significant decline left by the Corona Covid-19 pandemic, the results showed that appropriate strategies must be followed that target the internal tourism markets in order to attract more tourists by providing various services and entertainment at the same time, at competitive prices with diversification of promotional activities and marketing through social networking sites, in addition to attention to monitoring, evaluation and follow-up of tourist destinations and attention to their cleanliness

Optical properties of the massive Vanadium dioxide

We can easily extract the optical properties from a material starting from its permittivity complexes Ô‘; . The real part of this dielectric function clearly takes its place in the Colombian interaction of an exciton. We are interested in exciton 1S in the case of the massive vanadium dioxide. We will solve Schrdingers equation for this exciton by variational method and we obtain  according to energy E of the same exciton. We make a simulation by means of the Maple software of and of the index of refraction n according to energy E of the exciton 1S, around and far from the band gap of this material while being based on the approximation of the effective mass. We will extract the reflectivity R and transmittivity T of the massive vanadium dioxide for the normal incidence of the incidental photons by considering a slightly absorbent semiconductor state

Optical properties of a thin layer of the Vanadium dioxide at the metal state

The vanadium dioxide VO? currently became very motivating for the nanotechnologies’ researchers. It makes party of the intelligent materials because these optical properties abruptly change semiconductor state with metal at a critical temperature ? = 68 °C. This transition from reversible phase is carried out from a monoclinical structure characterizing its semiconductor state at low temperature towards the metal state of this material which becomes tétragonal rutile for ? > 68°????; it is done during a few nanoseconds. Several studies were made on this material in a massive state and a thin layer. We will simulate by Maple the constant optics of a thin layer of VO? thickness z = 82 nm for the metal state according to the energy ? of the incidental photons in the energy interval: 0.001242 ? ? (ev) ? 6, from the infra-red (I.R) to the ultra-violet (U.V) so as to be able to control the various technological nano applications, like the detectors I.R or the U.V, the intelligent windows to increase the energy efficiency in the buildings in order to save the cost of energy consumption by electric air-conditioning and the paintings containing nano crystals of this material. The constant optics, which we will simulate, is: the index of refraction, the reflectivity, the transmittivity, the coefficient of extinction, the dielectric functions ?1 real part and ?2 imaginary part of the permittivity complexes ? of this material and the coefficient absorption.&nbsp

Optical properties of the Vanadium dioxide

The vanadium dioxide is a material thermo chromium which sees its optical properties changing at the time of the transition from the phase of semiconductor state†” metal, at a critical temperature of 68°C. The study of the optical properties of a thin layer of VOâ‚‚ thickness 82 nm, such as the dielectric function, the index of refraction, the coefficient of extinction, the absorptions coefficient, the reflectivity, the transmittivity, in the photonic spectrum of energy ω located in the interval: 0.001242 ≤ ω (ev) ≤ 6, enables us to control well its practical utility in various applications, like the intelligent panes, the photovoltaic, paintings for increasing energy efficiency in buildings, detectors of infra-red (I.R) or ultra-violet (U.V). We will make simulations with Maple and compare our results with those of the literatur