Mathematical Model of Bridge-Linked Photovoltaic Arrays Operating Under Irregular Conditions

Este artículo presenta un procedimiento matemático para modelar un arreglo fotovoltaico (N filas y M columnas) en configuración puente-vinculado operando en condiciones regulares o irregulares. Dicho procedimiento usa el modelo ideal de un diodo para representar cada modulo fotovoltaico y la ecuación de Shockley para representar cada diodo de desviación. Para plantear el sistema de NxM ecuaciones no lineales requerido para obtener los voltajes de cada modulo, el modelo propuesto aplica la ley de corrientes de Kirchhoff a cada nodo interno del arreglo y la ley de voltajes de Kirchhoff a: cada lazo creado en la parte superior de una conexión entre dos columnas consecutivas y a cada columna con respecto al voltaje del arreglo. Además, el modelo provee un procedimiento para obtener la matriz Jacobiana para reducir el tiempo de solución del sistema de ecuaciones. El modelo circuital de dos arreglos (pequeño: 3x3 y mediano: 20x3) fue implementado en Simulink para validar el modelo. La exactitud y mejora en la velocidad de cálculo del modelo propuesto permite su uso para realizar evaluaciones energéticas de arreglos en puente vinculado o su comparación con otras configuraciones típicas, lo cual puede ser útil en el diseño de plantas fotovoltaica.This paper presents a mathematical procedure to model a photovoltaic array (N rows and M columns) in bridge-linked configuration operating under regular and irregular conditions. The proposed procedure uses the ideal single-diode model representation for each photovoltaic module and the Shockley equation to represent each bypass diode. To pose the system of NxM non-linear equations required to obtain the voltages of each module of the array, the proposed model apply the Kirchhoff current law to each internal node of the array and the Kirchhoff voltage law to: each loop created in the upper part of each connection of two consecutive strings and each string with respect to the output voltage of the array. Moreover, the model provide a procedure to obtain the Jacobian matrix to reduce the solution time of the equation system. The circuital model of two arrays (small: 3x3 and medium: 20x3) were implemented in Simulink to validate the proposed model. The accuracy and improved calculation speed of the proposed model allow its use to perform energetic evaluations of bridge-linked arrays or its comparison with other typical array configurations, which can be useful in the designing of photovoltaic plants

Photovoltaic battery charger with sliding mode control and charging current derivative limitation

En los sistemas fotovoltaicos (PV) aislados, los cargadores de baterías son importantespara garantizar el suministro de energía cuando la luz solar no está disponible. Dichoscargadores necesitan realizar el seguimiento del punto de máxima potencia (MPPT) ylimitar la derivada de corriente de carga de las baterías para extender su vida útil. Esteartículo propone un sistema cargador de baterías compuesto por un convertidor Buck, uncontrol en cascada de la corriente de las baterías y la tensión del panel PV, y la técnica deMPPT Perturbar y Observar (P&O). El P&O genera la referencia de tensión del panel parael lazo externo del control en cascada, implementado con un regulador P, cuya acción decontrol es la referencia de la corriente de carga de las baterías. Dicha referencia de corrientepasa por un limitador de derivada antes de llegar al lazo interno de control de corriente delas baterías, el cual es implementado con un control por modos deslizantes (SMC). Elartículo incluye el análisis de transversalidad y alcanzabilidad del SMC, así como elprocedimiento de diseño del regulador P. El sistema propuesto se valida por medio desimulaciones en el software PSIM mostrando la capacidad de realizar el MPPT y limitar laderivada de corriente de carga de las baterías al mismo tiempo.In stand-alone photovoltaic (PV) systems, battery chargers are important to guaranteethe energy supply when sunlight is not available. Such chargers need to track the maximumpower point (MPPT) and limit the derivative of the batteries’ charging current to extendtheir lifetime. This paper proposes a battery charging system composed of a Buck converter,a cascade control of the battery current and the PV panel voltage, and the Perturb andObserve (P&O) MPPT technique. P&O generates the reference of the panel voltage for theexternal loop of the cascade control implemented with a P regulator, whose control action isthe reference of the batteries’ charging current. Such current reference passes through aderivative limiter before reaching the internal current control loop, which is implementedby a sliding-mode controller (SMC). This paper includes transversality and reachabilityanalyses of the SMC, as well as the procedure to design the P regulator. The proposedsystem is validated by simulations in PSIM software to show its capacity to perform MPPTand limit the battery’s charging current derivative at the same time

Caribbean Corals in Crisis: Record Thermal Stress, Bleaching, and Mortality in 2005

BACKGROUND The rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin. METHODOLOGY/PRINCIPAL FINDINGS Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles. CONCLUSIONS/SIGNIFICANCE Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate.This work was partially supported by salaries from the NOAA Coral Reef Conservation Program to the NOAA Coral Reef Conservation Program authors. NOAA provided funding to Caribbean ReefCheck investigators to undertake surveys of bleaching and mortality. Otherwise, no funding from outside authors' institutions was necessary for the undertaking of this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Marine Biodiversity in the Caribbean: Regional Estimates and Distribution Patterns

This paper provides an analysis of the distribution patterns of marine biodiversity and summarizes the major activities of the Census of Marine Life program in the Caribbean region. The coastal Caribbean region is a large marine ecosystem (LME) characterized by coral reefs, mangroves, and seagrasses, but including other environments, such as sandy beaches and rocky shores. These tropical ecosystems incorporate a high diversity of associated flora and fauna, and the nations that border the Caribbean collectively encompass a major global marine biodiversity hot spot. We analyze the state of knowledge of marine biodiversity based on the geographic distribution of georeferenced species records and regional taxonomic lists. A total of 12,046 marine species are reported in this paper for the Caribbean region. These include representatives from 31 animal phyla, two plant phyla, one group of Chromista, and three groups of Protoctista. Sampling effort has been greatest in shallow, nearshore waters, where there is relatively good coverage of species records; offshore and deep environments have been less studied. Additionally, we found that the currently accepted classification of marine ecoregions of the Caribbean did not apply for the benthic distributions of five relatively well known taxonomic groups. Coastal species richness tends to concentrate along the Antillean arc (Cuba to the southernmost Antilles) and the northern coast of South America (Venezuela – Colombia), while no pattern can be observed in the deep sea with the available data. Several factors make it impossible to determine the extent to which these distribution patterns accurately reflect the true situation for marine biodiversity in general: (1) highly localized concentrations of collecting effort and a lack of collecting in many areas and ecosystems, (2) high variability among collecting methods, (3) limited taxonomic expertise for many groups, and (4) differing levels of activity in the study of different taxa

Lalinet Network Status

LALINET (Latin American Lidar Network) follows its goal to consolidation as a federative lidar network to provide regional coverage over Latin America in providing aerosol and greenhouse gas profiles following QA/QC protocols and promoting the development of researchers and students in atmopheric science field. We show recent results on different approaches for studying the optical properties of the atmosphere regarding aerosols at tropospheric and stratospheric level and greenhouse gas mixing ratio profiles followed by our recent support and validation efforts towards present and future satellite missions

Lalinet Network Status

LALINET (Latin American Lidar Network) follows its goal to consolidation as a federative lidar network to provide regional coverage over Latin America in providing aerosol and greenhouse gas profiles following QA/QC protocols and promoting the development of researchers and students in atmopheric science field. We show recent results on different approaches for studying the optical properties of the atmosphere regarding aerosols at tropospheric and stratospheric level and greenhouse gas mixing ratio profiles followed by our recent support and validation efforts towards present and future satellite missions

Monitoring stabilizing procedures of archaeological iron using electrochemical impedance spectroscopy

A methodology for monitoring washing procedures applied to stabilize archaeological iron is described. It is based on the combination of voltammetry of microparticles (VMP) with electrochemical impedance spectroscopy (EIS). A semi-empirical approach is used where the impedances at low and high frequencies were related with the fraction areas of passive and corrosion layers generated during the stabilizing treatment, the thickness, and the porosity of the corrosion layer. The variation of such parameters with the time of washing was determined from EIS data for four types of desalination procedures using concentrated NaOH and/or Na2SO3 aqueous solutions on archaeological iron artifacts. After 2 months of treatment, EIS data indicate that an essentially identical “stable” state was attained in all cases, as confirmed by the formation of a passive magnetite layer identified in VMP measurements while the rate of variation of corroded surface and porosity at short washing times varied significantly from one stabilization procedure to another.Peer Reviewe

Caribbean corals in crisis: Record thermal stress, bleaching, and mortality in 2005

Background: The rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin. Methodology/Principal Findings: Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the iming and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles. Conclusions/Significance: Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate