635 research outputs found

    Advanced Signal Processing Techniques Applied to Power Systems Control and Analysis

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    The work published in this book is related to the application of advanced signal processing in smart grids, including power quality, data management, stability and economic management in presence of renewable energy sources, energy storage systems, and electric vehicles. The distinct architecture of smart grids has prompted investigations into the use of advanced algorithms combined with signal processing methods to provide optimal results. The presented applications are focused on data management with cloud computing, power quality assessment, photovoltaic power plant control, and electrical vehicle charge stations, all supported by modern AI-based optimization methods

    the case study of TWIST project

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    Power quality requirements and responsibilities at the point of connection

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    In the present power delivery environment, electricity as a product has become more competitive than before. Modern electrical devices are complex in terms of their functionalities and are more sensitive to the quality of the supplied electricity. A disturbance in supply voltage can cause significant financial losses for an industrial customer. Moreover, there are increasing number of disputes in different countries of the world among the network operators, the customers and the device manufacturers regarding their individual responsibility concerning 'Power Quality' (PQ) problems and solutions. In addition, the existing standards on PQ give very limited information about responsibility sharing among the involved parties. PQ disturbances can be originated in the network as well as at the customer's premises and can propagate to other parts of the network. The PQ level in the network is also highly influenced by PQ emission behaviors of customer's devices and the network characteristics. During the last decades, PQ related complaints have increased largely. Inadequate PQ can lead to various technical and financial inconveniences to the customers and the network operators. This research aims to find out a socio-economically optimum solution to PQ problems. The main objectives of this thesis are defined as: "Analyze main PO problems and their consequences to various involved parties in the network. Next, define optimal PQ criteria at the customer's point of connection (POC) and finally specify responsibilities of the involved parties". The thesis is based on practical field measurements of PQ parameters in the network, on analyzing the developed network models by using computer simulations and laboratory experiments. The most important part of the work is the verification of simulation results with thepractical measurements. Further, the obtained results are compared with the values given in the available standards. Lastly optimal PQ parameters at a poc are defined for flicker, harmonics and voltage dips. A summary of the research work reported in this thesis is as follows: • Obtained a deeper insight in PQ problems around the world • Developed typical network models for computer simulations on different PQ phenomena (such as flicker, harmonics and voltage dips) and verified the results with field measured data • Gathered practical information on various technical and financial consequences of inadequate PQ for different parties namely: the network operators, the customers and the equipment manufacturers • Made an inventory on various existing (and developing) standards and technical documents on PQ around the world. Then, compared the limits given on various PQ parameters in those standards/documents and discussed their relevance and applicability in the future • A proposal is given about optimal PQ limits (for flicker, harmonics) at the low voltage (LV) customer's POC Also, the average and maximum values of voltage dips in the networks are estimated • Suitable planning level limit values for flicker, harmonics and voltage dips are proposed • PQ related responsibilities of the customers, network operators and device manufacturer at the customer's POC are defined The main conclusions and thesis contributions are: • It is found that a harmonization among the presently available PQ standards is required and a dedicated set of global standards is needed to get optimal PQ at the customer's POC Various limiting values on different PQ parameters (e.g. flicker emission and harmonic current emission limits for a customer) at a POC are proposed in this thesis. Also, the average and maximum numbers of voltage dips in the Dutch high voltage (HV) and medium voltage (MV) networks are estimated. • A new set of planning level values for flicker severities at different voltage levels of a network is proposed. For harmonics, a proposal is given to change the planning level values for 'triple n' harmonic voltages and new values are suggested for the MV and LV networks. Moreover, it was proposed that the 3rd harmonic summation coefficient value of the standard can be modified to a higher value as sufficient diversity is found in the system. Regarding voltage dips, the numbers of planning and compatibility levels are proposed for a MV network in the Netherlands. In this thesis, PQ responsibility sharing procedures are defined for a network operator, customer and a device manufacturer. Network impedance is identified as an important parameter in deciding flicker and harmonics at a POC The network operator should provide information on the approximate number of occurrence of voltage dips in a year at a customer's POC To maintain sufficient PQ level in the network, all the involved parties should follow certain rules and duties. It was concluded that PQ regulation can be successfully implemented in the electricity business when all the involved parties are aware of their respective responsibilities in the network

    Metric for seleting the number of topics in the LDA Model

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    The latest technological trends are driving a vast and growing amount of textual data. Topic modeling is a useful tool for extracting information from large corpora of text. A topic template is based on a corpus of documents, discovers the topics that permeate the corpus and assigns documents to those topics. The Latent Dirichlet Allocation (LDA) model is the main, or most popular, of the probabilistic topic models. The LDA model is conditioned by three parameters: two Dirichlet hyperparameters (α and β ) and the number of topics (K). Determining the parameter K is extremely important and not extensively explored in the literature, mainly due to the intensive computation and long processing time. Most topic modeling methods implicitly assume that the number of topics is known in advance, thus considering it demands an exogenous parameter. That is annoying, leaving the technique prone to subjectivities. The quality of insights offered by LDA is quite sensitive to the value of the parameter K, and perhaps an excess of subjectivity in its choice might influence the confidence managers put on the techniques results, thus undermining its usage by firms. This dissertation’s main objective is to develop a metric to identify the ideal value for the parameter K of the LDA model that allows an adequate representation of the corpus and within a tolerable elapsed time of the process. We apply the proposed metric alongside existing metrics to two datasets. Experiments show that the proposed method selects a number of topics similar to that of other metrics, but with better performance in terms of processing time. Although each metric has its own method for determining the number of topics, some results are similar for the same database, as evidenced in the study. Our metric is superior when considering the processing time. Experiments show this method is effective.As tendências tecnológicas mais recentes impulsionam uma vasta e crescente quantidade de dados textuais. Modelagem de tópicos é uma ferramenta útil para extrair informações relevantes de grandes corpora de texto. Um modelo de tópico é baseado em um corpus de documentos, descobre os tópicos que permeiam o corpus e atribui documentos a esses tópicos. O modelo de Alocação de Dirichlet Latente (LDA) é o principal, ou mais popular, dos modelos de tópicos probabilísticos. O modelo LDA é condicionado por três parâmetros: os hiperparâmetros de Dirichlet (α and β ) e o número de tópicos (K). A determinação do parâmetro K é extremamente importante e pouco explorada na literatura, principalmente devido à computação intensiva e ao longo tempo de processamento. A maioria dos métodos de modelagem de tópicos assume implicitamente que o número de tópicos é conhecido com antecedência, portanto, considerando que exige um parâmetro exógeno. Isso é um tanto complicado para o pesquisador pois acaba acrescentando à técnica uma subjetividade. A qualidade dos insights oferecidos pelo LDA é bastante sensível ao valor do parâmetro K, e pode-se argumentar que um excesso de subjetividade em sua escolha possa influenciar a confiança que os gerentes depositam nos resultados da técnica, prejudicando assim seu uso pelas empresas. O principal objetivo desta dissertação é desenvolver uma métrica para identificar o valor ideal para o parâmetro K do modelo LDA que permita uma representação adequada do corpus e dentro de um tempo de processamento tolerável. Embora cada métrica possua método próprio para determinação do número de tópicos, alguns resultados são semelhantes para a mesma base de dados, conforme evidenciado no estudo. Nossa métrica é superior ao considerar o tempo de processamento. Experimentos mostram que esse método é eficaz

    Control contributions to the universal operation of wind turbines

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    Ante la creciente dependencia energética de los países de la Unión Europea y los informes de contaminación atmosférica, la generación distribuida mediante energías renovables está modificando el sistema eléctrico actualmente basado en el paradigma centralizado. Dentro de las energías renovables con mayor impacto actual se encuentra la energía eólica. Un aspecto importante a mejorar en el marco de la calidad de potencia por parte del operador de la red de transmisión, es la continuidad del suministro. En estas circunstancias se define el concepto de microgrid como un sistema compuesto de al menos una fuente de generación distribuida asociada a cargas locales que pueden intencionalmente desconectarse del sistema de distribución con el objetivo de mejorar la fiabilidad del suministro. Este trabajo introduce la Operación Universal de aerogeneradores, donde éstos pueden trabajar conectados a red eléctrica y desconectarse de ella cuando ocurre un hueco o interrupción del suministro operando en modo isla. Es una aplicación específica del concepto de microgrid a aerogeneradores que evita el uso de sistemas de almacenamiento empleando únicamente las capacidades de almacenamiento y disipación intrínsecas de los aerogeneradores y se centra en contrarrestar interrupciones del suministro eléctrico del orden de unidades de minutos. Este trabajo se centra en abordar la problemática asociada a la Operación Universal de aerogeneradores desde el punto de vista del control de los convertidores de potencia: regulación del balance energético, compartición de la carga y control de la tensión local en modo isla y transiciones suaves entre modos de operación. Además, el sistema debe seguir manteniendo un rendimiento óptimo en modo conectado a red respetando los códigos de red: respuesta en potencia, calidad de potencia y respuesta ante perturbaciones

    Electric Power Conversion and Micro-Grids

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    This edited volume is a collection of reviewed and relevant research chapters offering a comprehensive overview of recent achievements in the field of micro-grids and electric power conversion. The book comprises single chapters authored by various researchers and is edited by a group of experts in such research areas. All chapters are complete in themselves but united under a common research study topic. This publication aims at providing a thorough overview of the latest research efforts by international authors on electric power conversion, micro-grids, and their up-to-the-minute technological advances and opens new possible research paths for further novel developments

    Impact of vehicle to grid in the power system dynamic behaviour

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    This work was supported in part by FCT-Fundação para a Ciência e a Tecnologia de Portugal, under the grant SFRH/BD/47973/2008 and within the framework of the Project "Green Island" with the Reference MIT-PT/SES-GI/0008/2008, by the European Commission within the framework of the European Project MERGE - Mobile Energy Resources in Grids of Electricity, contract nr. 241399 (FP7) and by INESC Porto - Instituto de Engenharia de Sistemas e Computadores do PortoTese de doutoramento. Sistemas Sustentáveis de Energia. Universidade do Porto. Faculdade de Engenharia. 201

    Virtual Synchronous Generator Operation of Full Converter Wind Turbine ‒ Control and Testing in a Hardware Based Emulation Platform

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    Wind is one of the most promising renewable energy forms that can be harvested to into the electrical power system. The installation has been rising worldwide in the past and will continue to steadily increase. The high penetration of wind energy has bought about a number of difficulties to the power system operation due to its stochastic nature, lack of exhibited inertia, and differing responses to the traditional energy sources in grid disturbances. Various grid support functions are then proposed to resolve the issues. One solution is to allow the renewable energy sources to behave like a traditional synchronous generator in the system, as a virtual synchronous generator (VSG). On the other hand, testing the control of the future power grid with high penetration renewable often relies on digital simulation or hardware-based experiments. But they either suffer from fidelity and numerical stability issues, or are bulky and inflexible. A power electronics based power system emulation platform is built in the University of Tennessee. This Hardware Testbed (HTB) allows testing of both system level and component level controls, with a good balance between the fidelity of the hardware-based testing platform, and the coverage of the digital simulation.This dissertation proposal investigates the VSG operation of the full converter wind turbine (FCWT), focusing on its control and testing in the HTB. Specifically, a FCWT emulator was developed using a single converter to include its physical model and control strategies. The existing grid support functions are also included to demonstrate their feasibility.The comprehensive VSG controls are then proposed for a FCWT with short term energy storage. The dynamic response of the FCWT can be comparable to the traditional generation during grid disturbance. The control can also allow the FCWT to be dispatched by the system operator, and even operate stand-alone without other grid sources.To study the system response under faults, a short circuit fault emulator was developed in the HTB platform. Four basic types of the short circuit faults with various fault impedance can be emulated using the emulator. The power system transient stability in terms of critical clearing time can be measured using the developed fault emulator

    Photovoltaic and Wind Energy Conversion Systems

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    In the first decades of the current millennium, the contribution of photovoltaic and wind energy systems to power generation capacity has grown extraordinarily all around the world; in some countries, these systems have become two of the most relevant sources to meet the needs of energy supply. This Special Issue deals with all aspects of the development, implementation, and exploitation of systems and installations that operate with both sources of energy
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