1,893 research outputs found
Power Converters and Control Systems for DC Smart Grids and Smart Transformers Applications
No full textThe recent rapid growth of renewable energy technologies, such as solar photovoltaic (PV) and wind turbines, are changing the nature of transmission, distribution and utilization of electrical energy. Most of the electrical loads-lighting, adjustable speed motors, brushless DC motors, computing and communication equipment are more compatible with DC power. Most distributed renewable energy generator including solar PV, wind, fuel cell, produce DC voltage. Thus DC power has great potential for increased compatibility with high-penetration, distribution-connected solar PV and other Distributed Renewable Energy Generators (DREGs). Trying to foresee the possible future scenarios of the power systems, it can be noticed that DC Smart Grids with its structure enables interconnection of different kind of sources requiring different voltage levels due to integration of different renewable sources, loads and energy storage devices, hence the DC Multibus provide a viable solution. A DC Multibus operating at different voltage levels can provide flexibility and redundancy to a DC Smart Grid.
The role of a Single-Star-Bridge-Cell Modular Multilevel Cascaded Converter (SSBC MMCC) for the creation of a DC Multibus has been investigated and its model, from the switching function to the small signal model, has been studied and verified in detail. A proper control system has been designed in order to manage voltage regulation and power balance. The performances of the system have been verified in simulation and experimental results in the particular case of a 5-level SSBC MMCC confirming the validity of the proposed solution and the robustness of the control system in a wide range of loads variations (up to 50% of power unbalance operating condition). The SSBC MMCC is combined with DC/DC converters in order to extent the operating voltage range.
Looking at the DC Smart Grids, the Dual Active Bridge (DAB) converters provide flexibility to the DC Multibus thanks to the possibility to extend the voltage range operation and to ensure galvanic isolation avoiding faults propagation. The DAB converter has been investigated and its model, from the switching function to the small signal model, has been studied and verified with simulation and experimental results. A proper control system has been designed in order to manage its output voltage. The use of the DAB converter becomes necessary in other examples of DC Smart Grids such in a More Electric Aircraft (MEA) where volume and weight optimization is a critical issue.
An advanced active rectifier for a MEA has been proposed in this thesis. It is based on a SSBC MMCC consisting of four single-phase H-Bridge cells for each phase. The system is coupled to four DAB converters providing output voltage equal to 270V in compliance with the aircraft standards. The proposed topology exhibits high power quality performances with a THD(%) of injected current equal to 3.5%, since the operation of the power conversion stage is characterized by a virtual switching frequency of 80 kHz in case of rated frequency of 400 Hz. High performances are guaranteed also in case of load changes and frequency variations in the range 360-800 Hz.
Besides high efficiency, high power density is another of the main goals related to the power generation and distribution in MEA. As a consequence, the number of the power conversion stages has to be reduced at the least in order to reach this target. Isolated DC/DC converters topologies can provide the required high voltage gain: 270V/28V.
A 270/28 V SiC MOSFET DAB converter has been proposed for MEA applications. An investigation about the thermal behaviour of the converter in case of high ambient temperatures has been provided in order to verify compliance with harsh environments conditions. Feasible operation of the DAB converter can be guaranteed for ambient temperatures over 100°C thanks to the superior performances of the SIC MOSFETs. Further improvements have been obtained in case of optimization of the power stage or using more advanced modulation techniques. A significant efficiency improvement of the 2% at light load is obtained through the Trapezoidal Modulation technique instead of the traditional Phase Shift Modulation. A further improvement is achieved in case of a hybrid realization based on SiC MOSFETs plus Si automotive qualified MOSFETs instead of an all-SiC DAB converter. However, when specifications require high switching frequencies together with reduced size of the cooling system and harsh operation, the all-SiC DAB converter is the preferable choice.
Finally, a possible three stages Smart Transformer (ST) is developed based on a SSBC MMCC converter in the Medium Voltage (MV) side and several DABs converters in the isolation stage. On the basis of the thermal monitoring information of the power conversion cells, a power routing techniques can be used in order to increase the reliability of the ST. The overall small signal model for such ST is derived and a new voltage balance control operating in the isolation stage has been compared with the classical MV voltage balance control. It has been demonstrated that the balancing in the isolation stage can achieve a significantly higher bandwidth than in the commonly applied MV stage. The superior dynamic performances are verified by simulation and experimental results on a ST with a 5-levels SSBC MMCC. The validity of the proposed voltage balance control has been remarked in a new ST start-up procedure, where the balance voltage condition is verified during all the start-up (also when the SSBC MMCC is not already turned on) since the control is demanded to the DAB converters
Dynamic study of a photovoltaic power plant interconnected with the grid
No full textThe drop of prices of photovoltaic technology has attracted investors to develop medium and large scale photovoltaic power plants (PVPPs). Because of the extent of land occupied by these PVPPs, the solar radiation along the plant is different. This situation causes several problems into the grid. Thus, the objective of this paper is to analyse the effect of a 6 MW PVPP at the point of common coupling considering different ambient conditions for each array. Three study cases are analysed considering temperatures of 10 °C, 30 °C and 40 ° C. In all the cases, the solar radiation is different in each array. The simulation and the results are conducted to understand the impact of ambient conditions in voltage, frequency and active power at the point of common coupling in a weak grid
Effect of Variable Solar Irradiance on the Reactive Power Response of Photovoltaic Generators
No full textNew grid requirements for large scale photovoltaic power plants (LS-PVPPs) demanding ancillary services make necessary the enhancement of photovoltaic (PV) generator's control. One of the challenges is the reactive power control despite the variable conditions. The aim of this paper is to present the response of reactive power considering the PV generator's capability curves and variable ambient conditions when maximum power point tracker (MPPT) is used for the active power control. For this purpose, a single PV generator of 0.6 MVA is simulated in DIgSILENT PowerFactory®. The results show that the active and reactive power varies with the ambient conditions
Dynamic modelling and control of a PV generator for large scale applications
No full textAs large scale photovoltaic power plants are increasing their capacity, the new grid codes are requiring that these power plants have similar performance as conventional power plants do. Because of this, it is essential to study the performance of these power plants under different solar irradiance, temperature and electrical characteristics. As the basic unit of these type of power plants are the PV generators, the present study explains in detail the model of a PV generator: PV array, the DC bus, the PV inverter, the filter and the transformer. The control method for active and reactive power is also explained and considers the variation of ambient conditions plus the capability curves of PV generators. Finally, some simulations are developed to validate the model
Como a história das crianças de rua do Senegal atravessa as fronteiras
No full textO seguinte artigo registra a fala da atriz Patricia Gomis e da diretora Sylvie Baillon sobre seu espetáculo Petit Bout de Bois, seu processo de criação e seu contexto social e histórico, durante o evento 3º Pro-Vocação - Encontro Internacional sobre Formação no Teatro de Animação. Patricia fala sobre como a realidade das crianças que vivem na rua do Senegal dialoga com sua própria experiência de vida e com a extorsão e a escravidão que diversos países africanos ainda sofrem
El péndulo físico o compuesto
No full textDescripción de un pénduo físico y su estudio dinámico.https://polimedia.upv.es/visor/?id=8168f824-77a4-7642-84b1-20718ef36f39Gomis Hilario, O. (2009). El péndulo físico o compuesto. https://riunet.upv.es/handle/10251/514
Um olhar sobre o jornalismo
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão, Programa de Pós-Graduação em Jornalismo, Florianópolis, 2009Este trabalho objetiva demonstrar como o cinema hollywoodiano, produzido entre 1930 e 2000, representa o jornalismo. Para tanto, foram escolhidos, como objeto de análise, 14 filmes sobre jornalismo, a saber: Aconteceu Naquela Noite, Fúria, Adorável Vagabundo, Cidadão Kane, A Montanha dos Sete Abutres, A Embriaguez do Sucesso, O Homem que Matou o Facínora, Paixões que Alucinam, A Primeira Página, Rede de Intrigas, Ausência de Malícia, Sob Fogo Cerrado, O Quarto Poder, O Informante; e como referencial para a análise, quatro pressupostos teóricos: as transformações de ordem tecnológica pelas quais passou o jornalismo, baseada na relação que Carlos Eduardo Franciscato constrói entre jornalismo e história social do tempo; a teoria do comentário público, de Lorenzo Gomis; as questões éticas, de acordo com a visão de Francisco Karam; e a abordagem de Walter Lippmann sobre estereótipos. Utilizando como metodologia de pesquisa a análise de conteúdo, foi possível tomar os filmes como referência ilustrativa das teorias em questão, para identificar e analisar como fundamentos do jornalismo são representados pelo cinema americano do século XX
Estudio del comportamiento térmico de una construcción para ensayos al aire libre
No full textTrabajo científico técnico. Mediante el estudio del comportamiento térmico de dos recintos que están expuestos al aire libre, el proyecto se propone investigar métodos de reducción de la demanda energética en los edificios de nueva construcción o rehabilitación, a través de la cuantificación del ahorro energético según los sistemas pasivos utilizados.Santamaría Gomis, J. (2011). Estudio del comportamiento térmico de una construcción para ensayos al aire libre. https://riunet.upv.es/handle/10251/11698.Archivo delegad
The welfare effects of private sector participation in Guinea's urban water supply
No full textIn 1989 the government of Guinea enacted far-reaching reform of its water sector, which had been dominated by a poorly run public agency. The government signed a lease contract for operations and maintenance with a private operator, making a separate public enterprise responsible for ownershipof assets and investment. Although based on a successful model that had operated in Cote d'Ivoire for nearly 30 years, the reform had many highly innovative features. It is being transplanted to several other developing countries, so the authors evaluate its successes and failures in the early years of reform. They present standard performance measures and results from a cost-benefit analysis to assess reform's net effect on various stakeholders in the sector. They conclude that, compared with what might have been expected under continued public ownership, reform benefited consumers, the government, and, to a lesser extent, the foreign owners or the private operator. Most sector performance indicators improved, but some problems remain. The three most troublesome areas are water that is unaccounted for (there are many illegal connections and the quality of infrastructure is poor), poor collection rates, and high prices. The weak institutional environment makes it difficult to improve collection rates, but the government could take some steps to correct the problem. To begin with, it could pay its own bills on time. Also, the legislature could authorize the collection of unpaid bills from private individuals.Water Conservation,Environmental Economics&Policies,Water and Industry,Economic Theory&Research,Payment Systems&Infrastructure,Environmental Economics&Policies,Water and Industry,Water Supply and Sanitation Governance and Institutions,Water Conservation,Town Water Supply and Sanitation
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