With an increasing capacity of inverter-based generation and with a 100% renewable energy power system on the horizon, grid forming converters have the potential to become the prevalent control mode ...in the grid. Thus, the correct performance of these devices is going to be crucial for system stability and security of supply. Most research related to the grid-forming control is focused on normal operating conditions, although significant effort has been devoted to current limitation strategies to ensure Low Voltage Ride Through (LVRT) capability. However, most contributions usually consider only balanced faults. This paper, proposes a new current limiting method based on the well-known threshold virtual impedance (TVI) that keeps the voltage source behaviour associated to the grid forming (GFM) capability, even when the current limit is reached, while reducing the voltage unbalance according to user-defined settings.
Las empresas actualmente demandan sistemas de costos que reporten un mayor detalle en la información generada, con el propósito de orientar la aplicación de estrategias que conduzcan a captar y ...apropiarse de mayores espacios de mercado, sobre todo cuando la competitividad es elevada; por ello, se formuló un sistema de costos basado en actividades, conocido por sus siglas en inglés como ABC (Activity-Based Costing), aplicado a los hoteles de turismo de cuatro estrellas de Mérida, en Venezuela, para el control y reducción de costos en los servicios prestados. A partir de una investigación de carácter exploratorio, con un diseño de campo y con apoyo docu-mental, se halló que el sector hotelero encuentra en el ABC una oportunidad para afinar controles sobre los altos y variados costos en los que incurre a partir del conocimiento profundo de actividades consumidas, con sus medidas y frecuencia. De esta manera, se obtiene el costo real de los distintos servicios al vincularlos con las actividades desarrolladas para su obtención; finalmente, se sugiere un conjunto de variables que pudieran fungir como generadoras de valor e indicadoras de eficiencia. Se concluye que el ABC representa una herramienta de gestión que orienta las decisiones estratégicas y el control de los costos con la consecuente reducción de los mismos para la maximización de beneficios.
To ensure power system stability in the presence of a high penetration of power-electronic interfaced resources, Transmission System Operators (TSOs) require access to transparent, reliable and ...validated dynamic models to be able to conduct comprehensive large-scale studies. One possible approach is the utilization of so-called generic models that offer a modular structure capable of representing a wide range of installations by appropriately adjusting the parameters. This paper provides a thorough comparison of the two predominant generic models for Type 4 Wind Turbine (WT), developed by the International Electrotechnical Commission (IEC) and the Western Electric Coordinating Council (WECC), respectively. It highlights both the shared functionalities and the notable differences between these models, offering insights into their applicability. Furthermore, this analysis identifies unresolved questions regarding their implementation, emphasizing the need for further clarification to ensure a common understanding of their structure and consistent behavior across different tools.
•This work presents a detailed comparison of IEC/WECC type 4 wind turbine models.•A visual side-to-side comparison in a harmonized structure facilitates analyses.•Simulations investigate the origin of specific differences in behavior.•Recommendations for updates in both models’ documentations are made.
This paper discusses the performance assessment of new secondary voltage regulators currently under study in France to address challenges posed by the energy transition. With renewable integration ...and increasing cross-border interconnections, power flow variations surge across the network. Coupled with the historical SVRs’ relatively slow response, operational since the late 1970s, recent observations show higher voltage volatility. Prior research has already highlighted the potential of two novel regulators: the Average Q-SVR and the LQ-SVR, in mitigating these issues. Our focus here centres on the latter and begins by discussing the implications of control design hypotheses on closed-loop system performance. These include linearisation, neglecting communication delays, and assuming uniform dynamic behaviour across all resources. We then propose a two-step control design, leveraging Linear Quadratic Regulator (LQR) and eigenstructure placement methods and demonstrate that this approach surpasses the LQR method alone in terms of transient reactive power tracking.
•Analysis of the control design hypothesis on closed-loop system performance.•Proposal for a two-step control design, leveraging Linear Quadratic Regulator (LQR) and eigenstructure placement methods.•Performance assessment of the Linear Quadratic Regulator in simulation using Dynaωo tool.
This paper presents a new Matlab toolbox, aimed at facilitating the use of polynomial optimization for stability analysis of nonlinear systems. In the past decade several decisive contributions made ...it possible to recast this type of problems as convex optimization ones that are tractable in modest dimensions. However, available software requires their user to be fluent in Sum-of-Squares programming, preventing them from being more widely explored by practitioners. To address this issue, SOStab entirely automates the writing and solving of optimization problems, and directly outputs relevant data for the user, while requiring minimal input. In particular, no specific knowledge of optimization is needed for implementation. The toolbox allows a user to obtain outer and inner approximates of the Region of Attraction (RoA) of the operating point of different grid connected devices such as synchronous machines and power converters.
•SoStab is a toolbox that gives Region of Attraction for non linear dynamical systems.•It makes Sums-of-square programming more accessible to untrained users.•SOStab gives outer and inner approximations of finite horizon Region of Attraction.•Two cases show how to use it for transient stability assessment of power systems.
Normal bone remodeling is maintained by a balance between osteoclast and osteoblast activity, whereas defects in osteoclast activity affecting such balance result in metabolic bone disease. ...Macrophage-macrophage fusion leading to multinucleated osteoclasts being formed is still not well understood. Here we present PEG-induced fusion of macrophages from both U937/A and J774 cell lines and the induced differentiation and activation of osteoclast-like cells according to the expression of osteoclast markers such as tartrate resistant acid phosphatase (TRAP) and bone resorptive activity. PEG-induced macrophage fusion, during the non-confluent stage, significantly increased the osteoclastogenic activity of macrophages from cell lines compared to that of spontaneous cell fusion in the absence of PEG (polyethylene glycol). The results shown in this work provide evidence that cell fusion per se induces osteoclast-like activity. PEG-fused macrophage differential response to pretreatment with osteoclastogenic factors was also examined in terms of its ability to form TRAP positive multinucleated cells (TPMNC) and its resorptive activity on bovine cortical bone slices. Our work has also led to a relatively simple method regarding those previously reported involving cell co-cultures. Multinucleated osteoclast-like cells obtained by PEG-induced fusion of macrophages from cell lines could represent a suitable system for conducting biochemical studies related to basic macrophage fusion mechanisms, bone-resorption activity and the experimental search for bone disease therapeutic alternatives.
Frequency constrained unit commitment Cardozo, Carmen; Capely, Laurent; Dessante, Philippe
Energy systems (Berlin. Periodical),
02/2017, Letnik:
8, Številka:
1
Journal Article
Recenzirano
The unit commitment (UC) problem deals with the short-term schedule of the electrical generation to meet the power demand. The main objective is to minimize the production cost, while respecting ...technical and security constraints. In addition to the system load, a specific amount of spare capacity is committed to cope with uncertainties, such as forecasting errors and unit outages; this is called reserve and it has been traditionally specified following a static reliability criterion. In a system with a conventional generation mix, this security constraint allows one to obtain UC solutions that naturally provide an acceptable transient response. However, the increasing penetration of variable generation sources, such as wind and solar, can lead to UC solutions that no longer ensure system security. Thus, enhanced security constraints have been proposed to consider the power system dynamics when optimising the day-ahead generation schedule. Some published works are focused on the formulation of these constraints in a mixed-integer linear programming structure to apply classic optimisation techniques. Nevertheless, power system dynamics is a non-linear problem, and, to the authors’ knowledge, the limits of these linear approximations have not been discussed in literature. This work examines the ability of different UC models to produce secure schedules when facing unit outages, through the implementation of a set of primary reserve and energy co-optimisation models. These models are built based on linear approximations of dynamic constraints that are available in recent literature. Then, dynamic simulations are performed for every conceivable outage to observe the transient response of a test system and to quantify the risk of under frequency load shedding. It is shown that the system’s need for frequency regulation depends on the operating point and that enforcing a fixed reserve, inertia or maximal frequency slope constraint is not cost/effective to limit the dynamic risk. If used, these values should be set on an hourly basis by iteration between the optimisation and the dynamic simulator.
Desde sus orígenes, la Ingeniería de Tejidos ha buscado diversos materiales que puedan ser utilizados para la generación de soportes que sirvan para el anclaje, proliferación y diferenciación celular ...que conduzcan a la obtención de tejidos humanos. Muchos materiales de tipo cerámico, polimérico y metálico se han evaluado, pero hasta la fecha muchos de ellos han sido rechazados por diversas razones, entre otras su escasa biocompatibilidad y biodegradabilidad, la respuesta inmune generada, la baja resistencia mecánica o el riesgo de transmisión de virus o priones. El fibrinógeno es una proteína presente en el plasma sanguíneo que puede ser utilizada para la generación de soportes tridimensionales que favorezcan el crecimiento de células; se obtiene a partir del propio paciente, bancos de sangre o como proteína purificada (TisseelR o TissucolR, Laboratorios Baxter). El fibrinógeno evita el desencadenamiento de una respuesta inmunológica y el uso de productos xenogénicos. Debido a la estructura proteica, la adhesión y proliferación celular se ven favorecidas dando excelentes resultados en la generación de equivalentes de piel, cartílago, córnea y reemplazos cardiacos en aplicaciones in vitro e in vivo. Como desventajas presenta su rápida degradación y su baja resistencia mecánica; sin embargo, en los últimos años se han venido evaluando mezclas con algunos biopolímeros como ácido poliláctico (PLLA), ácido poli-glicólico (PGA) y alginato de sodio. Esta revisión presenta algunas de las principales aplicaciones del fibrinógeno en Ingeniería de Tejidos.
El propósito de la presente investigación documental y descriptiva, es fijar posición acerca de la eficiencia del mercado de valores venezolano. En Venezuela, el órgano regulador en esta materia es ...la Superintendencia Nacional de Valores (SNV). El hecho de que en el mercado de valores se oferte una gama de instrumentos financieros que sirvan como fuente opcional de capital e inversión, garanticen liquidez en sus operaciones y sus participantes perciban en este seguridad y transparencia, son las bases fundamentales sobre las que descansa la eficiencia de un mercado. Por ello y en función de la hipótesis de los mercados eficientes, la cual fija su atención en el grado en que el mercado provee información sin necesidad de incurrir en costos de transacción adicionales, se concluye que el mercado de valores venezolano posee un nivel débil e intermedio, ya que la información necesaria para hacer análisis, tanto técnicos como fundamentales, está a disposición de cualquier agente dentro del mencionado sistema. Por otra parte, la opinión última del inversor es la que prevalece en correspondencia al perfil de riesgo que presente y se inclinará por lo tanto hacia una estrategia de inversión pasiva en la medida en que crea que el mercado es en sí mismo eficiente.
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