236 research outputs found

    A review of recent control techniques of drooped inverter‐based AC microgrids

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    As the penetration of distributed generation (DG) systems in the grid is increasing, the challenge of combining large numbers of DGs in the power systems has to be carefully clarified and managed. The control strategy and management concept of the interconnected systems should be flexible and reliable to handle the various types of DGs. This can be suitably met by microgrids. This paper introduces the microgrid structure and elements and states the main objectives that should be achieved by the microgrid controllers and each DG controller in both operation modes (grid-connected and island mode). It also presents the challenges of having multiple DG units in a microgrid in terms of accurate power control/sharing, voltage and frequency regulation, power management between DGs, different renewable energy sources integration and deployment, seamless mode transfer, and the modeling issues. The centralized and decentralized control techniques as potential solutions have been discussed and compared by highlighting the advantages and disadvantages of each. Furthermore, the recent control techniques for drooped alternating current microgrids and the main proposed solutions and contributions in the literature have been exposed to finally overcome the droop control limitations and obtain a flexible and smart distributed power system

    Smart power conditioners for electric railway power grids

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    Programa doutoral em Engenharia Eletrónica e de Computadores (especialidade de Eletrónica de Potência e Energia)Railway transport presents itself as one of the greatest economic and social drivers of several nations in the world. Furthermore, it is considered the safest means of land transport, with the electric rail system being efficient and environmentally friendly. However, for the inclusion of more and larger electric locomotives, it is necessary to increase the capacity of the railway supply systems. This doctoral thesis intends to contribute to the development of power electronics solutions capable of increasing the capacity of railway supply systems. As such, a power electronics converter connected in a neutral section located between two traction power substations (TPS) is proposed. The proposed algorithm makes it possible to dynamically balance the average active powers of the two substations, mitigating overload problems. In the event of deceleration or braking of a locomotive on one side, it is possible to use the energy from this regenerative braking to assist another locomotive on the other side of the neutral section. Moreover, the proposed solution still presents the interface with a photovoltaic solar system and an energy storage system. In this way, it is possible to minimize energy dependence on the power grid, as well as to include renewable energy sources. The storage system also makes it possible to store surplus production or energy from regenerative braking for later use. The proposed solution is validated with the help of computer simulations considering a real implementation scale. The simulation model is based on cascaded multilevel modular converters, with each submodule also featuring solid-state transformers. Considering a reduced-scale prototype developed in the laboratory, computer simulations of the prototype are also presented and discussed. The document also presents a chapter that portrays all the steps taken for the implementation of the reduced-scale sectioning post-Rail Power Conditioner (sp-RPC) laboratory prototype. Once its implementation was completed, its experimental validation was carried out, proving the correct functioning of the system based on the proposed algorithm.O transporte ferroviário apresenta-se como um dos maiores impulsionadores económicos e sociais de várias nações do mundo. Para além disso, é considerado como o meio de transporte terrestre mais seguro, sendo o sistema ferroviário elétrico eficiente e amigo do ambiente. Contudo, para a inclusão de mais e maiores locomotivas elétricas é necessário aumentar a capacidade dos sistemas de alimentação ferroviários. Esta tese de doutoramento pretende contribuir com o desenvolvimento de soluções de eletrónica de potência capazes de aumentar a capacidade dos sistemas de alimentação ferroviários. Como tal, é proposto um conversor de eletrónica de potência conectado numa secção neutra que se encontra entre duas subestações de tração de energia. A algoritmia proposta permite equilibrar as potências ativas médias das duas subestações de forma dinâmica, mitigando os problemas de sobrecarga. Na ocorrência de uma desaceleração ou travagem de uma locomotiva num dos lados, é possível utilizar a energia proveniente desta travagem regenerativa para o auxílio de marcha de outra locomotiva existente no outro lado da secção neutra. Não obstante, a solução proposta apresenta ainda a interface com um sistema solar fotovoltaico e um sistema de armazenamento de energia. Desta forma, é possível minimizar a dependência energética da rede elétrica, bem como incluir fontes de energia renovável. O sistema de armazenamento permite ainda armazenar o excedente de produção ou a energia proveniente de uma travagem regenerativa para posterior utilização. O conceito proposto é estudado com auxílio de simulações computacionais considerando uma escala de implementação real. O modelo de simulação é baseado em conversores modulares multinível em cascata, sendo que cada sub-módulo apresenta ainda transformadores de estado sólido. Considerando um protótipo de pequena escala desenvolvido em laboratório, simulações computacionais do protótipo são igualmente apresentadas e validadas. O documento apresenta ainda um capítulo que retrata todos os passos realizados para a implementação do protótipo laboratorial do sectioning post-Rail Power Conditioner (sp-RPC) de pequena escala. Uma vez finalizada a sua implementação, procedeu-se à sua validação experimental, comprovando o correto funcionamento do sistema com base na algoritmia proposta.This work has been supported by FCT — Fundação para a Ciência e Tecnologia, within the R&D Units Project Scope UIDB/00319/2020. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018, granted by the Portuguese FCT foundation

    Power Quality in Electrified Transportation Systems

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    "Power Quality in Electrified Transportation Systems" has covered interesting horizontal topics over diversified transportation technologies, ranging from railways to electric vehicles and ships. Although the attention is chiefly focused on typical railway issues such as harmonics, resonances and reactive power flow compensation, the integration of electric vehicles plays a significant role. The book is completed by some additional significant contributions, focusing on the interpretation of Power Quality phenomena propagation in railways using the fundamentals of electromagnetic theory and on electric ships in the light of the latest standardization efforts

    Design and Control of Power Converters 2019

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    In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

    Wide Bandgap Based Devices

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    Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits

    ECOS 2012

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    The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

    Microgrids/Nanogrids Implementation, Planning, and Operation

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    Today’s power system is facing the challenges of increasing global demand for electricity, high-reliability requirements, the need for clean energy and environmental protection, and planning restrictions. To move towards a green and smart electric power system, centralized generation facilities are being transformed into smaller and more distributed ones. As a result, the microgrid concept is emerging, where a microgrid can operate as a single controllable system and can be viewed as a group of distributed energy loads and resources, which can include many renewable energy sources and energy storage systems. The energy management of a large number of distributed energy resources is required for the reliable operation of the microgrid. Microgrids and nanogrids can allow for better integration of distributed energy storage capacity and renewable energy sources into the power grid, therefore increasing its efficiency and resilience to natural and technical disruptive events. Microgrid networking with optimal energy management will lead to a sort of smart grid with numerous benefits such as reduced cost and enhanced reliability and resiliency. They include small-scale renewable energy harvesters and fixed energy storage units typically installed in commercial and residential buildings. In this challenging context, the objective of this book is to address and disseminate state-of-the-art research and development results on the implementation, planning, and operation of microgrids/nanogrids, where energy management is one of the core issues

    Fase Anizdun bihurgailuentzako modulazio berriak

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    266 p.Los convertidores multifase han adquirido una gran relevancia debido a sus ventajas sobre los convertidores trifásicos convencionales. Debido a estas ventajas, destacando la tolerancia a fallos, los sistemas multifase se emplean cada vez más en aplicaciones donde la fiabilidad es un factor clave. Sin embargo, estos sistemas no son inmunes a las faltas y, por ello, deben tomarse medidas que aumenten su fiabilidad y robustez. En concreto, esta tesis hace frente a dos de los mayores causantes de faltas en los sistemas basados en motores eléctricos (las faltas por circuito abierto y las faltas en los rodamientos debido a la tensión del modo común) mediante el uso de técnicas de modulación. Por un lado, en caso de perder una de las fases, las técnicas de modulación permiten generar tensiones equilibradas a la salida del convertidor, permitiendo a su vez que el convertidor siga funcionando aunque de forma degradada. Por otro lado, la tensión de modo común generada debido a la conmutación de los dispositivos que forman el convertidor daña los rodamientos de la máquina eléctrica. Por ello, siendo los rodamientos una pieza clave del motor, es necesario desarrollar nuevas técnicas de modulación que minimicen los efectos de la tensión de modo común. De esta forma, esta tesis, además de analizar en profundidad las fuentes causantes de las faltas mencionadas, propone nuevas técnicas de modulación capaces de mejorar el comportamiento del convertidor ante dichos problemas, con el fin de mejorar la tolerancia a fallos del convertidor y alargar la vida útil de los rodamientos del motor

    Delta STATCOM with partially rated energy storage for intended provision of ancillary services

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    This thesis presents research on two distinct areas, where the work carried out in the first half highlights the challenges posed by the declining system inertia in the future power systems and the potential capability of the energy storage systems in bridging the gap, supporting a safe and reliable operation. A comparison of various energy storage technologies based on their specific energy, specific power, response time, life-cycle, efficiency, cost and further correlating these characteristics to the timescale requirements of frequency and RoCoF services showed that supercapacitors (SC) and Li-ion batteries present the most suitable candidates. Results of a network stability study showed that for a power system rated at 2940 MVA with a high RES contribution of 1688 MVA, equating to 57% of the energy mix, during a power imbalance of 200 MW, an ESS designed to provide emulated inertia response (EIR) in isolation required a power and energy rating of 39.54 MW and 0.0365 MWh respectively. Similarly, providing primary frequency response (PFR) on its own required a power and energy rating of 114.52 MW and 2.14 MWh respectively. ESS providing these services in isolation was not able to maintain all the frequency operating limits and similar results were also seen in the case of the recently introduced Dynamic Containment service. However, with the introduction of a combined response capability, a significantly improved performance, comparable to that of the synchronous generators was observed. In order to maintain the RoCoF and the statutory frequency limit of 0.5 Hz/s and ±0.5 Hz respectively, an ESS must be able to respond with a delay time of no more than 0.2 seconds and be able to ramp up to full response within 0.3 seconds (0.5 seconds from the start of contingency) for a frequency deviation of ±0.5 Hz. The second half of the thesis focused on investigating the current state-of-the-art power conversion system topologies, with the objective of identifying a suitable topology for interfacing ESSs to the grid at MV level. A delta-connected Modular Multilevel STATCOM with partially rated storage (PRS-STATCOM) is proposed, capable of providing both reactive and active power support. The purpose is to provide short-term energy storage enabled grid support services such as inertial and frequency response, either alongside or temporarily instead of standard STATCOM voltage support. The topology proposed here contains two types of sub-modules (SM) in each phase-leg: standard sub-modules (STD-SMs) and energy storage element sub-modules (ESE-SMs) with a DC-DC interface converter between the SM capacitor and the ESE. A control structure has been developed that allows energy transfer between the SM capacitor and the ESE, resulting in an active power exchange between the converter and the grid. A 3rd harmonic current injection into the converter waveforms was used to increase the amount of power that can be extracted from the ESE-SMs and so reduce the required ESE-SMs fraction in each phase-leg. Simulation results demonstrate that for three selected active power ratings, 1 pu, 2/3 pu, & 1/3 pu, the fraction of SMs that need to be converted to ESE-SMs are only 69%, 59% & 38%. Thus, the proposed topology is effective in adding real power capability to a STATCOM without a large increase in equipment cost. Furthermore, modifying the initially proposed topology with the use of Silicon Carbide (SiC) switching devices and interleaved DC-DC interface converter with inverse coupled inductors resulted in similar efficiencies when operated in STATCOM mode.Open Acces

    Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

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    Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems
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