Suppression of Second-Order Harmonic Current for Droop-Controlled Distributed Energy Resource Converters in DC Microgrids

Droop-controlled distributed energy resource converters in dc microgrids usually show low output impedances. When coupled with ac systems, second-order harmonics typically appear on the dc-bus voltage, causing significant harmonic currents at the converters resource side. This paper shows how to reduce such undesired currents by means of notch filters and resonant regulators included in the converters control loops. The main characteristics of these techniques in terms of harmonic attenuation and stability are systematically investigated. In particular, it is shown that the voltage control-loop bandwidth is limited to be below twice the line frequency to avoid instability. Then, a modified notch filter and a modified resonant regulator are proposed, allowing to remove the constraint on the voltage loop bandwidth. The resulting methods (i.e., the notch filter, the resonant regulator, and their corresponding modified versions) are evaluated in terms of output impedance and stability. Experimental results from a dc microgrid prototype composed of three dc-dc converters and one dc-ac converter, all with a rated power of 5kW, are reported

Exploring children online risk situation in Uruguay’

Internet se ha convertido finalmente en "el tejido de nuestras vidas", tal como lo anunciaba en 2001 Manuel Castells, arraigándose en casi todas las dimensiones de esta como el trabajo, estudio, entretenimiento y ciudadanía, entre otras. De la misma manera internet es en un elemento relevante en la vida e niños y adolescentes, quienes al 2015 representaban un tercio de los internautas globales y se conectan cada vez a edades más tempranas. Esto ha ignificado grandes oportunidades pero también desafíos para garantizar la protección de estos en el espacio virtual, convirtiéndose esta en una creciente reocupación para los gobiernos, las escuelas y los adultos familiares. La temática es más aún compleja ya que estudios muestran que el nivel de dominio de internet por parte de menores de edad y la probabilidad de estos encuentren riesgos en dicho espacio están positivamente relacionados. El gobierno de Uruguay creó una "revolución digital" única a nivel global, ya que en 4 años prácticamente todos los niños y adolescentes tuvieron acceso a una omputadora e internet con el programa de gobierno, Plan Ceibal. Ceibal facilitó muchas oportunidades pero al mismo tiempo podría sugerirse que amplificó las amenazas en línea para menores. Los principales beneficiarios de Ceibal provienen de familias de nivel socioeconómico bajo, cuyos adultos familiares no contaban en la mayoría de los casos con experiencia previa con el uso de tecnologías digitales. Asimismo Ceibal representó un desafío para los docentes, ya ue en varios casos también accedían a una computadora por primera vez. Este estudio utiliza la literatura de referencia en el campo de la protección en línea de menores para estudiar el caso uruguayo explorando en qué medida las particularidades del Plan Ceibal y del contexto local pueden amplificar o restringir los riesgos que menores pueden experimentar al utilizar internet. Se argumentará que es relevante que el gobierno implemente estrategias educativas que aborden temas no exclusivamente vinculadas al uso de TIC, especialmente enfocadas en atender la violencia en centros educativos y educación sexual, ya que los riesgos en línea en sectores más vulnerables de la población podrían estar amplificándose debido a un déficit en este sentido.Agencia Nacional de Investigación e Innovació

Microbial Zoopoetics in Octavia Butler’s Clay’s Ark

This paper reads Octavia Butler’s 1984 novel Clay’s Ark as a speculative handbook for living collaboratively in a more-than-human world. Drawing on Aaron Moe’s theory of zoopoetics, as well as emerging research on the effects of the human microbiome on health, behavior, and personality, I consider how the novel’s “villain,” an infectious microbe, might be not just a germ but an author, writing difference into the text of the human species. Depicting this interspecies relationship as both troubling and productive, Butler suggests the urgent need for humans to construct responsible and mutually beneficial forms of collaboration with their nonhuman neighbors of all sorts

Finding Ferality in the Anthropocene: Marie Darrieussecq’s “My Mother Told Me Monsters Do Not Exist”

What will it take to undomesticate the world—to begin to loosen humanity’s tight grasp on the planet’s spaces, structures, resources, and populations? Marie Darrieussecq’s short story “My Mother Told Me Monsters Do Not Exist” describes the intrusion of an unidentifiable creature into a fastidious woman’s apartment home, a modest but powerful scene of undomestication. This brief tale illustrates the intertwined forces of domestication and feralization that link humans and animals and proposes interspecies companionship as a lively and productive site of ferality in the regimented unwildness of the Anthropocene

Plug and Play DC-DC Converters for Smart DC Nanogrids with Advanced Control Ancillary Services

This paper gives a general view of the control possibilities for dc-dc converters in dc nanogrids. A widely adopted control method is the droop control, which is able to achieve proportional load sharing among multiple sources and to stabilize the voltage of the dc distribution bus. Based on the droop control, several advanced control functions can be implemented. For example, power-based droop controllers allow dc-dc converters to operate with power flow control or droop control, whether the hosting nanogrid is operating connected to a strong upstream grid or it is operating autonomously (i.e., islanded). Converters can also be equipped with various supporting functions. Functions that are expected to play a crucial role in nanogrids that fully embrace the plug-and-play paradigm are those aiming at the monitoring and tuning of the key performance indices of the control loops. On-line stability monitoring tools respond to this need, by continuously providing estimates of the stability margins of the loops of interest; self- tuning can be eventually achieved on the basis of the obtained estimates. These control solutions can significantly enhance the operation and the plug-and-play feature of dc nanogrids, even with a variable number of hosted converters. Experimental results are reported to show the performance of the control approaches

Analysis of an On-Line Stability Monitoring Approach for DC Microgrid Power Converters

An online approach to evaluate and monitor the stability margins of dc microgrid power converters is presented in this paper. The discussed online stability monitoring technique is based on the Middlebrook's loop-gain measurement technique, adapted to the digitally controlled power converters. In this approach, a perturbation is injected into a specific digital control loop of the converter and after measuring the loop gain, its crossover frequency and phase margin are continuously evaluated and monitored. The complete analytical derivation of the model, as well as detailed design aspects, are reported. In addition, the presence of multiple power converters connected to the same dc bus, all having the stability monitoring unit, is also investigated. An experimental microgrid prototype is implemented and considered to validate the theoretical analysis and simulation results, and to evaluate the effectiveness of the digital implementation of the technique for different control loops. The obtained results confirm the expected performance of the stability monitoring tool in steady-state and transient operating conditions. The proposed method can be extended to generic control loops in power converters operating in dc microgrids

Synthesis and characterization of metal oxide nanoparticles

Nanoparticles of CuO, Co3O4 and Mn5O 8 were prepared via sol-gel chemical routes. Thermal treatments of the gels were used to obtain particles of different sizes, as determined by the widths of the Bragg lines in x-ray diffraction. To prepare CuO nanoparticles, a Cu(OH)2 gel was first produced by reacting copper nitrate with sodium hydroxide, followed by annealing the gel at temperatures between 160°C to 1,000°C to produce particles in the 6 to 36 nm range. Nanoparticles of Co3O4 in the size range of 9 to 45 nm were prepared in an analogous manner by reacting cobalt nitrate and sodium hydroxide. Similar procedures to produce nanoparticles of MnO resulted only in the synthesis of Mn3O4. Annealing Mn3O4 at 400°C for three hours produced nanoscale Mn5O8 (14nm), a difficult-to-prepare oxide. Using an electrochemical route, 30nm particles of NiO were also synthesized. Thermogravimetric measurements were used to identify the thermally-induced phase transformations and x-ray diffraction was used to identify the phases and determine the average particle sizes of the phases

Reconstructing Ohio\u27s Ancient Past One Pot Sherd at a Time

The primary focus of our research was to analyze, conserve, and reconstruct ancient prehistoric pottery from the Cramer Village Site, a Fort Ancient-era (AD 900-1200) site located on the west bank of the Scioto River in Union Township, Ross County, Ohio.https://engagedscholarship.csuohio.edu/u_poster_2012/1011/thumbnail.jp