Stability Analysis of Converter Control Strategies for Power Electronics-Dominated Power Systems

The electric power system, whose well-established structure consolidated over decades of studies is composed of large centralized generating units, transmission systems, and distributed loads, is currently experiencing a significant transformation, posing new challenges for its safe operation in the near future. The increasing amount of grid-connected power electronics-based converters associated with renewable energy sources, is reducing the amount of energy produced by means of conventional generating units, generally represented by large synchronous machines (SMs) directly connected to the grid. As a consequence, declining system inertia, as well as reduced fault currents affecting short-circuit level and retained voltage under fault conditions, are expected. This has caused concerns among system operators (SOs) worldwide about the stability of the future power system, triggering discussions in different countries about the need for new converter control strategies, which would allow safe system operation under the expected grid configuration. In this scenario, the concept of ”grid-forming (GFM) converters” has been recently proposed as a possible solution allowing high-penetration of power electronics-based generation. Initially introduced in the context of microgrids, the concept of GFM converters needs to be reviewed for applications in wide interconnected systems. Indeed, at the present time, a well-established formulation is still missing in the literature, and several committees worldwide are currently working on a definition for identifying the characteristics of such converters. Due to the initial concern of SOs related to declining system inertia, the concept of GFM converters has been often associated with the idea of virtual inertia, and namely the emulation of a synthetic inertial response by means of a power electronics-based converter. Yet, this is only one aspect related to the increase of power electronics-based generation, and the concept of a GFM converter includes other features, which, however, need to be properly specified in order to provide clear guidelines for manufacturers aiming to the development of suitable converter control strategies. This thesis addresses the topic of GFM converters from a control perspective, and aims to characterize potential features, as well as the relevant issues related to this technology. First, the characteristics of a GFM converter are identified according to an extensive literature overview, so that by reviewing international practice on this technology, a general formulation for a GFM converter control structure is identified. Particular emphasis is given to the synchronization principle adopted by the converter which, contrary to state-of-the-art grid-connected converters adopting a dedicated unit for grid synchronization purposes, is generally achieved in a GFM converter by reproducing the power-synchronization mechanism of a SM. An extensive small-signal stability analysis is performed in order to identify the implications of the identified converter behaviour on converter stability, as well as the effects due to the interactions between converters operating nearby. Finally, potential issues related to the implementation of a GFM converter are highlighted, and possible solutions are proposed, whose effectiveness is validated by means of hardware-in-the-loop (HIL) simulations, as well as experimental tests in a laboratory environment, by adopting power-HIL (PHIL) test benches

Geometric Modeling of Cellular Materials for Additive Manufacturing in Biomedical Field: A Review

Advances in additive manufacturing technologies facilitate the fabrication of cellular materials that have tailored functional characteristics. The application of solid freeform fabrication techniques is especially exploited in designing scaffolds for tissue engineering. In this review, firstly, a classification of cellular materials from a geometric point of view is proposed; then, the main approaches on geometric modeling of cellular materials are discussed. Finally, an investigation on porous scaffolds fabricated by additive manufacturing technologies is pointed out. Perspectives in geometric modeling of scaffolds for tissue engineering are also proposed

With good design, healthy backs : recommendations for the design and the production of healthy school furniture.

El mobiliario escolar puede constituir una concausa para la conformación saludable de la estructura ósea de niños y adolescentes. Este trabajo presenta un análisis de la postura sedente durante las actividades escolares; procura encontrar una relación entre el diseño del mobiliario utilizado actualmente en Mendoza y los factores posturales y rendimiento escolar de los alumnos. Dicho estudio fue subsidiado por la Secretaría de Ciencia, Técnica y Posgrado de la UNCUYO (SECTYP) en el período 2009-2011 y entre 2011-1013. Por su naturaleza, esta investigación es de característica ‘tecnológica’ aplicándose para su desarrollo el método propio de la Ergonomía basado en el "enfoque sistémico". Comprende las siguientes etapas: análisis y diagnóstico del mobiliario en uso, análisis de tareas, diseño de la propuesta, experimentación y validación. Se desarrollaron modelos de prueba bajo cánones ergonómicos de postura saludable para el aprendizaje, compuestos por silla y pupitre independientes. El resultado del estudio comprende una guía de recomendaciones para el diseño y la producción de mobiliario escolar saludable. El producto fue transferido a la Dirección General de Escuelas y el Ministerio de Infraestructura del Gobierno de Mendoza, y al Instituto Nacional de Tecnología Industrial (INTI), para su Programa de DiseñoThe school furniture can be a contributing cause to the formation of healthy bone structure of children and adolescents. This paper presents an analysis of the seated posture for school activities; try to find a relationship between furniture design currently used in Mendoza and postural factors and academic performance of students. This study was subsidized by the Ministry of Science,Technology and Graduate UNCUYO (SECTYP) in 2009-2011 and between 2011-1013. By its nature, this research is of "technology’ feature apply for own method development ergonomics based on the “systemic approach". Comprising the following steps: analysis and diagnosis of furniture in use, task analysis, proposal design, testing and validation. Test models were developed under ergonomic standards of healthy learning posture, composed of independent chair and desk. The result of the study includes a guide of recommendations for the design and production of healthy school furniture. The product was transferred to the Directorate General of Schools and the Ministry of Infrastructure of the Government of Mendoza, and the National Institute of Industrial Technology (INTI), for Program DesignFil: Del Rosso, Roxana. Universidad Nacional de Cuyo. Facultad de Artes y DiseñoFil: Tomasiello,Luis Roberto. Universidad Nacional de Cuyo. Facultad de Artes y Diseñ

El diseño desde las medidas humanas : concepción de una línea de instrumentos para la medición de personas

El conocimiento de los datos antropométricos de las personas es vital para el mejoramiento del nivel de calidad de vida y de las condiciones operativas de quienes interactúan con productos o se desempeñan en puestos laborales. Se plantea el diseño de un conjunto de aparatos para relevamientos antropométricos, compuesto por estadiómetro, calibres, plicómetros, goniómetros y valija porta-instrumentos, destinados a las poblaciones infantil, adulta y de la tercera edad. El trabajo se integra con la elaboración de una guía, para el uso correcto del referido equipamiento. Asimismo, se prevé que los aparatos puedan ser utilizados por profesionales de diferentes campos relacionados con el tema. El trabajo corresponde a un proyecto de investigación subsidiado por la SECyT, 2005-2007.Fil: Tomassiello, Roberto Luis. Universidad Nacional de Cuyo. Facultad de Artes y DiseñoFil: Del Rosso, Roxana. Universidad Nacional de Cuyo. Facultad de Artes y Diseñ

University teaching in healthy environments : ergonomic design for space and equipment

El trabajo plantea el estudio de ‘ambientes saludables’ en edificios de instituciones académicas, particularmente del campus de la Universidad Nacional de Cuyo. Su propósito es mejorar la calidad de vida, salud y seguridad de las personas en el trabajo. Se elaboraron propuestas como ‘guía de recomendaciones’ para el diseño y adquisición de equipamiento universitario. El método aplicado es el propio de la Ergonomía, incluyendo: análisis de tareas, desarrollo de propuestas, experimentación, validación, seguimiento. El resultado puede aplicarse a los edificios del contexto antes señalado y a otros similares, pudiendo transferirse asimismo a la enseñanza de la Ergonomía en diferentes disciplinas.The work presents the study of ‘healthy environments’ in academic buildings, particularly the campus of the Universidad Nacional de Cuyo. Its purpose is to improve the quality of life, health and safety of persons at work. Proposals were developed as a ‘guide recommendations’ for the design and acquisition of college teams. The method used is typical of ergonomics, including: task analysis, proposal development, testing, validation, monitoring. The result can be applied to the aforementioned context buildings and the like, can also be transferred to the teaching of ergonomics in different disciplines.Fil: Tomassiello, Roberto Luis. Universidad Nacional de CuyoFil: Del Rosso, Roxana. Universidad del Aconcagu

Las personas, sus medidas y el diseño : una propuesta de instrumentos para relevamientos antropométricos poblacionales

El conocimiento de los datos antropométricos de poblaciones específicas es crucial para el mejoramientode las condiciones de trabajo, así como del nivel de calidad de vida de las personas que interactúan con productos o puestos laborales. En este artículo se plantea el diseño de instrumentos para relevamientos antropométricos, cubriendo el siguiente target de usuarios: poblaciones infantil, adulta y de la tercera edad. Se prevé producir dichos instrumentos, orientándolos para ser usados por parte de diferentes profesionales relacionados con el tema. Igualmente, se asistirá a los usuarios con programas de entrenamiento y formación, para la utilización correcta del referido equipamiento.Fil: Tomassiello, Roberto Luis. Universidad Nacional de Cuyo. Facultad de Artes y DiseñoFil: Del Rosso, Roxana. Universidad Nacional de Cuyo. Facultad de Artes y Diseñ

Robust Stability Analysis of Synchronverters Operating in Parallel

Recent studies have shown how synchronization units of converters operating nearby may interact with each other, affecting the stability of the system. Synchronverters are able to self-synchronize to the grid without the need of a dedicated unit because they can reproduce the power synchronization mechanism of synchronous machines. Recently, the robust stability of a synchronverter has been investigated by means of structured singular values (commonly called μ-analysis). In this paper, μanalysis is performed to investigate how the robust stability of a synchronverter is affected by the presence of another converter of the same type operating in parallel. It is demonstrated that the parallel operation of synchronverters reduces their robust stability and a possible solution is proposed, based on the implementation of virtual impedances in the control algorithm. An accurate state-space model of the system under study is developed by adopting the component connection method and the robust stability analysis is validated against time-domain simulations in MATLAB/Simulink/PLECS and experimental results with a power-hardware-in-the-loop test bench

Robust Stability Investigation of the Interactions Among Grid-Forming and Grid-Following Converters

State-of-the-art grid-connected converters can be classified as “grid-following,” meaning that they require a dedicated synchronization unit in order to inject active and reactive currents into the grid. Recently, other converter control concepts have been proposed in the literature, such as the synchronverter, which can instead achieve synchronization without a dedicated unit and, within its physical limitations, make the converter behave as an ideal voltage source. Since it should be expected that the grid-connected converters having different control philosophies will coexist for many years, in this article, the interaction among the converters operating nearby are addressed. First, the component connection method (CCM) technique is introduced, as a means for obtaining the state-space representation of a complex system with several units operating nearby. Due to the complexity of the grid and the difficulty in obtaining its exact representation, μ-analysis is adopted in this article for assessing the robust stability of the converter under different operating conditions, according to a defined set of plant uncertainties. Simulation results and experimental tests in a laboratory environment by means of a power hardware-in-the-loop (PHIL) test bench are performed to demonstrate the validity of the presented analysis