Control de parques eólicos "offshore" conectados a red mediante enlace de continua HVdc-LCC

Los parques eólicos offshore tienen un gran potencial para convertirse en una fuente de energía a gran escala para la producción de electricidad. Los futuros proyectos para parques eólicos offshore tendrán un rango de capacidad instalada de 250MW hasta 1000MW, por lo que han de desarrollarse nuevos conceptos para todo el sistema eléctrico, incluyendo la transmisión dentro del parque, así como hacia la orilla y la integración con la red eléctrica. Sin embargo, los costes de inversión para implementar los parques eólicos offshore son muy elevados en comparación con las instalaciones que se podrían realizar en tierra. El sistema de transmisión hacia la costa implica casi el 30% de la inversión total de los parques eólicos offshore. Por lo tanto, su adecuado diseño es un factor muy importante que debe ser considerado. A medida que las distancias a la orilla se incrementan, también se incrementan los costes de los cables en corriente alterna (c.a.), volviéndose prohibitivos al superar ciertas distancias. Los cables c.a. de gran longitud producen grandes cantidades de potencia reactiva capacitiva y, por lo tanto, disminuyen la capacidad de transmisión. Dado su bajo coste, su sencillo diseño, su simple forma de operar y su bajo impacto en la red receptora, la interconexión mediante sistemas de transmisión HVdc puede ofrecer en estas aplicaciones algunas ventajas cuando se compara con las conexiones HVac. En respuesta a los citados retos, esta Tesis se presenta como una aportación original en la gestión, operación y control de un parque eólico offshore basado en aerogeneradores con generadores asíncronos doblemente alimentados (GADA) y conectados a la orilla por un sistema de transmisión de corriente continua a alta tensión HVdc conmutado por red (LCC). Se han desarrollado técnicas de control que permiten al aerogenerador, con GADA, coordinar su operación con el enlace HVdc-LCC. De igual forma, se ha analizado la gestión de potencia reactiva del sistema GADA-HVdc, todo lo cual se aborda como un problema de optimización.--------------------------------------------------------------------------------------------------------------------------------------------------------------------------Offshore wind farms have a great potential to become a large-scale source of energy for the production of electricity. Future project offshore wind farms will have an installed capacity range between 250MW and 1000MW and therefore new concepts must be developed for the entire electrical system, including both transmission within the park as well as to shore, and grid integration. However, the investment costs involved in offshore wind farms are very high when compared with those of onshore installations. The transmission system to shore entails nearly 30% of the overall investment of offshore wind farms and, consequently, its adequate design is an important factor to be considered. As the distances to shore increase, so do the costs of the alternating current (ac) power cables, which become prohibitive beyond certain distance. Long ac cables produce large amounts of capacitive reactive power, and therefore reduce the transmission capacity. In these applications, interconnection by means of high voltage dc (HVdc) transmission systems may offer some advantages when compared with high voltage ac (HVac) connections, due to their lower costs, plain design, simple operation procedures and low impact on the receiving power grid. As an answer to the mentioned challenges, this Thesis presents an original contribution for the management, operation and control of an offshore wind farms working with wind turbines based on doubly fed induction generator (DFIG) technologies, and with a line commutated converter high voltage dc (LCC-HVdc) transmission connection to the grid. Control techniques have been developed that allow the wind turbines based on DFIG, to coordinate its operation with the LCC-HVdc link. In the same way, the reactive power management of the DFIG-HVdc systems has been analyzed and dealt with as an optimization problem

Control of Variable Speed Wind Turbines with Doubly Fed Asynchronous Generators for Stand-Alone Applications

This paper addresses the design and implementation of a novel control of a variable speed wind turbine with doubly fed induction generator for stand-alone applications. In opposition to grid-tied applications, in stand-alone systems the voltage and frequency must be generated by the doubly fed induction generator. Therefore, a voltage and frequency controller is required for supplying the load at constant voltage and frequency. This controller is implemented by orientation of the generator stator flux vector along a synchronous reference axis. In this way, constant voltage and frequency is obtained and the generator will supply the active and reactive power demanded by the load, while the wind turbine will be responsible for achieving power balance in the system. Then, power control is assumed by the pitch actuator controlling the rotational speed of the wind turbine for power balancing. A load shedding mechanism is needed if the load power exceeds the maximum available wind power. Detailed simulation results are presented and discussed to demonstrate the capabilities and contributions of the proposed control scheme.This work has been supported by the I+D program for Research Groups of the Autonomous Community of Madrid under ref. S2013/ICE-2933.PublicadoPublicad

Optimal Power Transmission of Offshore Wind Power Using a VSC-HVdc Interconnection

High-voltage dc transmission based on voltage-source converter (VSC-HVdc) is quickly increasing its power rating, and it can be the most appropriate link for the connection of offshore wind farms (OWFs) to the grid in many locations. This paper presents a steady-state operation model to calculate the optimal power transmission of an OWF connected to the grid through a VSC-HVdc link. The wind turbines are based on doubly fed induction generators (DFIGs), and a detailed model of the internal OWF grid is considered in the model. The objective of the optimization problem is to maximize the active power output of the OWF, i.e., the reduction of losses, by considering the optimal reactive power allocation while taking into account the restrictions imposed by the available wind power, the reactive power capability of the DFIG, the DC link model, and the operating conditions. Realistic simulations are performed to evaluate the proposed model and to execute optimal operation analyses. The results show the effectiveness of the proposed method and demonstrate the advantages of using the reactive control performed by DFIG to achieve the optimal operation of the VSC-HVdc.This work has been supported by the I+D program for Research Groups of the Autonomous Community of Madrid under ref. S2013/ICE-2933.Publicad

Modeling and Control of LCC Rectifiers for Offshore Wind Farms Connected by HVDC Links

This paper presents a voltage and frequency control (VFC) and an average-value model (AVM) of a line-commutated converter for a rectifier station in an offshore wind farm (OWF) connected by a high-voltage direct current link. A capacitor bank is placed at the AC terminals of the rectifier station to perform VFC within the OWF. The proposed model uses the active and reactive power generated by the OWF as inputs, while the state variables are the voltage magnitude and phase angle at the capacitor bank bus. The proposed VFC is based on the orientation of the voltage vector at the capacitor bank bus toward a synchronous reference axis. It is then demonstrated that frequency control is achieved by regulating the reactive power balance at the capacitor bank bus, while voltage control is carried out by regulating the active power balance. Moreover, it is demonstrated that in a diode rectifier, although voltage cannot be controlled as in a thyristor rectifier, it is bounded within acceptable limits. In addition, small-signal study is performed to facilitate controller design and system stability analysis. VFC and the accuracy of the proposed AVM are validated by simulation, using both the proposed AVM and a detailed switching model

Coordinated control system between grid-vsc and a dc microgrid with hybrid energy storage system

Direct current microgrids (DCMGs) are currently presented as an alternative solution for small systems that feed sensitive electrical loads into DC. According to the scientific literature, DCMG maintains good voltage regulation. However, when the system is in islanded mode, very pronounced voltage variations are presented, compromising the system"s ability to achieve reliable and stable energy management. Therefore, the authors propose a solution, connecting the electrical network through a grid-tied voltage source converter (GVSC) in order to reduce voltage variations. A coordinated control strategy between the DCMG and GVSC is proposed to regulate the DC voltage and find a stable power flow between the various active elements, which feed the load. The results show that the control strategy between the GVSC and DCMG, when tested under different disturbances, improves the performance of the system, making it more reliable and stable. Furthermore, the GVSC supports the AC voltage at the point of common coupling (PCC) without reducing the operating capacity of the DCMG and without exceeding even its most restrictive limit. All simulations were carried out in MATLAB 2020

Fundação ontológica do mundo virtual a partir da filosofia de Nicolaï Hartmann

The following article presents a philosophical investigation into the ontological shaping ofthe virtual world. It is a theoretical contribution to the contemporary debate in the philosophy ofcomputation on the ontological characterization of digital computing and its emerging products,as it proposes an approach to this field of study from the philosophical perspective of NicolaïHartmann. The main objective of this article is to explain the stratification of the virtual world basedon Hartmann’s ontological theory of strata and categories. To achieve this goal, a critical review ofthe state of the art of the philosophical ontology of virtuality was carried out. Then we proceededto present a stratification and categorization proposal called ‘The virtual world factory’ which is ahermeneutic ontology of digital virtuality based on Hartmann’s postulates. The main conclusionsreached are: i) The emergence of virtual world reality is constituted of the same strata that makeup the sphere of real-world knowledge: material, organic, psychic and social. ii) Virtual reality is aproduct of computation that occurs in the sphere of knowledge in which there is intervention of theideal sphere and the sphere of the real world.En el siguiente artículo se presenta una investigación filosófica acerca de la conformación ontológica delmundo virtual. Esta es un aporte teórico al debate contemporáneo de la filosofía de la computación sobrela caracterización ontológica de la computación digital y sus productos emergentes, ya que se propone unaaproximación a este campo de estudio desde la perspectiva filosófica de Nicolaï Hartmann. El objetivo principal del presente artículo es explicar la estratificación del mundo virtual a partir de la teoría ontológica de estratos y categorías de Hartmann. Para cumplir con este objetivo se procedió a una revisión crítica del estado de la cuestión de la ontología filosófica de la virtualidad. Luego se procedió a presentar una propuesta de estratificación y categorización denominada ‘La fábrica del mundo virtual’ que es una ontología hermenéutica de la virtualidad digital basada en los postulados de Hartmann. Las principales conclusiones alcanzadas son: i) La emergencia de la realidad del mundo virtual se encuentra constituida de los mismos estratos que conforman la esfera del conocimiento del mundo real: material, orgánico, psíquico y social. ii) La realidad virtual es un producto de la computación que ocurre en la esfera del conocimiento en el que existe intervención de la esfera ideal y de la esfera del mundo real.O artigo seguinte apresenta uma investigação filosófica sobre a modelação ontológica de o mundo virtual. É uma contribuição teórica para o debate contemporâneo na filosofia de computação sobre a caracterização ontológica da computação digital e dos seus produtos emergentes, uma vez que propõe uma abordagem deste campo de estudo a partir da perspectiva filosófica de Nicolaï Hartmann. O principal objectivo deste artigo é explicar a estratificação do mundo virtual baseado sobre a teoria ontológica de Hartmann dos estratos e categorias. Para atingir este objectivo, uma revisão crítica de foi realizado o estado da arte da ontologia filosófica da virtualidade. Depois prosseguimos para apresentar uma proposta de estratificação e categorização chamada "A fábrica mundial virtual", que é uma ontologia hermenêutica da virtualidade digital com base nos postulados de Hartmann. As principais conclusões são: i) A emergência da realidade do mundo virtual é constituída pelos mesmos estratos que fazem no domínio do conhecimento do mundo real: material, orgânico, psíquico e social. ii) A realidade virtual é uma produto de computação que ocorre na esfera do conhecimento em que há intervenção do esfera ideal e a esfera do mundo real

Enhanced flat adenoma detection rate with high definition colonoscopy plus i-scan for average-risk colorectal cancer screening

Background and aim: The usefulness of high definition colonoscopy plus i-scan (HD+i-SCAN) for average-risk colorectal cancer screening has not been fully assessed. The detection rate of adenomas and other measurements such as the number of adenomas per colonoscopy and the flat adenoma detection rate have been recognized as markers of colonoscopy quality. The aim of the present study was to compare the diagnostic performance of an HD+i-SCAN with that of standard resolution white-light colonoscope. Methods: This is a retrospective analysis of a prospectively collected screening colonoscopy database. A comparative analysis of the diagnostic yield of an HD+i-SCAN or standard resolution colonoscopy for average-risk colorectal screening was conducted. Results: During the period of study, 155/163 (95.1%) patients met the inclusion criteria. The mean age was 56.9 years. Sixty of 155 (39%) colonoscopies were performed using a HD+i-SCAN. Adenoma-detection-rates during the withdrawal of the standard resolution versus HD+i-SCAN colonoscopies were 29.5% and 30% (p = n.s.). Adenoma/colonoscopy values for standard resolution versus HD+i-SCAN colonoscopies were 0.46 (SD = 0.9) and 0.72 (SD = 1.3) (p = n.s.). A greater number of flat adenomas were detected in the HD+i-SCAN group (6/60 vs. 2/95) (p < .05). Likewise, serrated adenomas/polyps per colonoscopy were also higher in the HD+i-SCAN group. Conclusions: A HD+i-SCAN colonoscopy increases the flat adenoma detection rate and serrated adenomas/polyps per colonoscopy compared to a standard colonoscopy in average-risk screening population. HD+i-SCAN is a simple, available procedure that can be helpful, even for experienced providers. The performance of HD+i-SCAN and substantial prevalence of flat lesions in our average-risk screening cohort support its usefulness in improving the efficacy of screening colonoscopies

Mice infectivity of Trypanosoma cruzi forms differentiated by culture in LIT medium.

Editorial. Ética, Bioética y MedicinaSalinas, Pedro JoséPrincipios activos y utilización terapéutica de las plantas tóxicas del género DaturaActive ingredients and therapeutical utilization of toxic plants of the genus Datura.Salinas, Pedro JoséBermúdez B., María MónicaEfecto de la glucosa sobre la expresión aeróbica de una fusión de operón moa::lac en Escherichia coli K12Glucose effect on the aerobic expression of a genomic moa::lac operon fusion in Escherichia coli K12l.Ortega de López, MariemmaEl origen de los biopotencialesTucci Reali, AlvaroTécnicas participativas en la educación sexual y cambios de conducta en adolescentesParticipative techniques in sexual education and behavior changes in adolescents.Rubio, IvánGranadillo Vera, DervisSalinas, Pedro JoséLa progresión de la enfermedad renal. Una revisiónThe progression of renal disease. A review.Rondón Nucete, MiguelLopez, PilarActitudes del profesional de la salud hacia los pacientes con SIDAHealth professional attitudes toward AIDS patients.Prieto Belisario, SoniaInfectividad en ratón de las formas de Trypanosoma cruzi diferenciadas por primocultivo en medio LITMice infectivity of Trypanosoma cruzi forms differentiated by culture in LIT medium.López Eyzarguirre, NelsonD'Jesús, RosaPrevalencia de Blastocystis hominis en pacientes sintomáticosPrevalence of Blastocystis hominis in symptomatic patients.Carrero Sulbarán, SarelieCarrero de Pérez, María C.Pérez Feo, MirnaCarrero Guerra, José ElielReflexiones sobre la dignidad del Educador MédicoRengel Sánchez, LuisXIV Congreso Venezolano de Ciencias Mé[email protected] analíticosemestra

Tipe of Feeding and Development of Weight and Height in Children Born Alive in The Area of Ambulatorio El Llano, Mérida, Venezuela.

Editorial. La edición de una revista de MedicinaSalinas, Pedro JoséDistorsión del Mapa Enzimático Hepático en la Hipervitaminosis K3 AgudaChanges in the enzyme pattern of the liver in the acute hypervitaminosis K3.Alarcón Corredor, Oscar MarinoSilva Larralte, TaniaPadrón, AleydaTauil B., EduarChavarría, RoviroCarnevali de Tatá, ElizabethLa Etnobotánica de Pteridium aquilinum (L.) Kuhn en Venezuela y sus posibles riesgos asociados de CarcinogénesisThe ethnobotany of Pteridium aquilinum (L.) Kuhn in Venezuela and possible associated carcinogenic risks.Ortega M., Francisco J.Tipo de Alimentación y Desarrollo Pondo-Estatural en Niños Nacidos Vivos del Área del Ambulatorio «El LLano», Mérida, VenezuelaTipe of Feeding and Development of Weight and Height in Children Born Alive in the Area Ambulatorio El Llano, Mérida, VenezuelaGranadillo Vera, DervisSalinas, Pedro JoséNava D'Jesús, LuisDelgado, IsabelArandia, JohnyEfecto de la fibra dietética no soluble sobre lípidos séricos en ratasEffect of dietetic fiber on the seric lipids of male and female ratsBastardo de Castañeda, GladysRamírez de Fernández, MaríaGarcía de Méndez, María GuadalupeMartens Cook, JorgeVías metabólicas en el músculo cardíaco de ratas sometidas a estrés hipobáricoMetabolic Pathway in the myocardial tissue of rats under hypobaric stress.Ramírez de Martens, LuisaLópez de Piña, DianaSuárez de León, LuzMartens Cook, JorgeCólera: Una revisión actualizada. Parte 3. Complicaciones del cólera. Tratamiento. Genética del cólera. Mecanismos de control de la epidemia. ReferenciasCholera: An updated review. Part 3. Cholera complications. Treatment. Genetics of cholera. Mechanisms for the control of the epidaemia. References.Salinas, Pedro JoséSemblanza. Dr. Rafael Pérez Clavierde Sardi, [email protected] analíticosemestra

Comparative clinical study after one year, in children born alive in the area of the Ambulatory Hospital El Llano, Mérida, Venezuela.

Editorial. Revista científica de la Facultad de Medicina. Creación y objetivos.The creation of MedULA, Journal of the Faculty of Medicine of the University of The Andes.Salinas, Pedro JoséEstudio clínico comparativo al término de un año de los niños nacidos vivos del área del Ambulatorio El Llano, Mérida, Venezuela.Comparative clinical study after one year, in children born alive in the area of the Ambulatory Hospital El Llano, Mérida, Venezuela.Granadillo Vera, DervisSalinas, Pedro JoséNava D'Jesús, LuisDelgado, IsabelArandia, JohnyMecanismos de control neural cardíaco en la Enfermedad de Chagas. Implicaciones terapéuticasCardiac autonomic control mechanisms in Chagas' heart disease. Therapeutic implicatioxis.Dávila S., Diego F.Donis, José H.Torres M., ArgenisArata de Bellabarba, GabrielaNavas, MaríaSardi, GalenoVásquez, Carlos J.Madariaga, WilliamGottberg, Carlos F.Rossell R., OsmanIntoxicación por PlomoLead intoxicationCastro Peñalver, Pedro ElíasConducta heterosexual en un grupo de estudiantes universitariosHeterosexual Behavior in a Group of University StudentsPérez Feo, MirnaSalinas, Pedro JoséReacciones psicológicas ante un desastre natural: La inundación de El LimónPsychological reactions to a natural disaster: The flood victims of El Limón Community.Romero García, OswaldoMorales de Romero, MaríaSemblanza. Dr. Antonio José Uzcátegui BurgueraSalinas, Pedro JoséNoticias del Centro de Investigaciones Psicoló[email protected] analíticosemestra