30 research outputs found

    Pem fuel cell modeling and converters design for a 48 v dc power bus

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    Fuel cells (FC) are electrochemical devices that directly convert the chemical energy of a fuel into electricity. Power systems based on proton exchange membrane fuel cell (PEMFC) technology have been the object of increasing attention in recent years as they appear very promising in both stationary and mobile applications due to their high efficiency, low operating temperature allowing fast startup, high power density, solid electrolyte, long cell and stack life, low corrosion, excellent dynamic response with respect to the other FCs, and nonpolluting emissions to the environment if the hydrogen is obtained from renewable sources. The output-voltage characteristic in a PEMFC is limited by the mechanical devices which are used for regulating the air flow in its cathode, the hydrogen flow in its anode, its inner temperature, and the humidity of the air supplied to it. Usually, the FC time constants are dominated by the fuel delivery system, in particular by the slow dynamics of the compressor responsible for supplying the oxygen. As a consequence, a fast load transient demand could cause a high voltage drop in a short time known as oxygen starvation phenomenon that is harmful for the FC. Thus, FCs are considered as a slow dynamic response equipment with respect to the load transient requirements. Therefore, batteries, ultracapacitors or other auxiliary power sources are needed to support the operation of the FC in order to ensure a fast response to any load power transient. The resulting systems, known as FC hybrid systems, can limit the slope of the current or the power generated by the FC with the use of current-controlled dc-dc converters. In this way, the reactant gas starvation phenomena can be avoided and the system can operate with higher efficiency. The purpose of this thesis is the design of a DC-DC converter suitable to interconnect all the different elements in a PEMFC-hybrid 48-V DC bus. Since the converter could be placed between elements with very different voltage levels, a buck-boost structure has been selected. Especially to fulfill the low ripple requirements of the PEMFCs, but also those of the auxiliary storage elements and loads, our structure has inductors in series at both its input and its output. Magnetically coupling these inductors and adding a damping network to its intermediate capacitor we have designed an easily controllable converter with second-order-buck-like dominant dynamics. This new proposed topology has high efficiency and wide bandwidth acting either as a voltage or as a current regulator. The magnetic coupling allows to control with similar performances the input or the output inductor currents. This characteristic is very useful because the designed current-controlled converter is able to withstand shortcircuits at its output and, when connected to the FC, it facilitates to regulate the current extracted from the FC to avoid the oxygen starvation phenomenon. Testing in a safe way the converter connected to the FC required to build an FC simulator that was subsequently improved by developing an emulator that offered real-time processing and oxygen-starvation indication. To study the developed converters and emulators with different brands of PEMFCs it was necessary to reactivate long-time inactive Palcan FCs. Since the results provided by the manual reactivation procedure were unsatisfactory, an automatic reactivation system has been developed as a complementary study of the thesis.En esta tesis se avanzo en el diseño de un bus DC de 48 V que utiliza como elemento principal de generación de energía eléctrica una pila de combustible. Debido a que la dinámica de las pilas de combustible están limitadas por sus elementos mecánicos auxiliares de control una variación rápida de una carga conectada a ella puede ocasionar daños. Es por esto que es necesario utilizar elementos almacenadores de energía que puedan suministrar estas rápidas variaciones de carga y convertidores para que gestionen de una forma controlada la potencia del bus DC. Durante la realización de pruebas de los convertidores es de gran importancia utilizar emuladores o simuladores de pilas de combustibles, esto nos permite de una forma económica y segura realizar pruebas criticas antes de conectar los convertidores a la pila. Adicionalmente una nueva topologia de convertidor fue presentada y ésta gestionará la potencia en el bu

    Solid state transformer technologies and applications: a bibliographical survey

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    This paper presents a bibliographical survey of the work carried out to date on the solid state transformer (SST). The paper provides a list of references that cover most work related to this device and a short discussion about several aspects. The sections of the paper are respectively dedicated to summarize configurations and control strategies for each SST stage, the work carried out for optimizing the design of high-frequency transformers that could adequately work in the isolation stage of a SST, the efficiency of this device, the various modelling approaches and simulation tools used to analyze the performance of a SST (working a component of a microgrid, a distribution system or just in a standalone scenario), and the potential applications that this device is offering as a component of a power grid, a smart house, or a traction system.Peer ReviewedPostprint (published version

    A variable duty cycle maximum power point tracking algorithm for wind energy conversion systems.

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    This thesis proposes a new Maximum Power Point Tracking (MPPT) algorithm employed in Wind Energy Conversion Systems (WECS). One of the major issues discussed in the literature concerning HCS is its inefficiency in detecting the peak power when there is a change in wind •speed. In addition, the HCS produces oscillations in delivered power once this peak is detected. A modified HCS algorithm is proposed in this thesis to overcome these limitations. This algorithm employs a variable duty cycle to reduce the oscillations in delivered power once the peak power is detected. The performance of the proposed algorithm was evaluated using MA TLAB-SIMULINK. Efficiencies of 95.48%, 98.8%, and 92.2% were observed under constant wind speed, abrupt wind speed change from 10m/s to 5m/s, and a continuously varying wind speed between 5m/s and 12m/s respectively. The traditional HCS algorithm was also simulated for comparison with efficiencies reduced to 76.27%, 81.35, and 67.86% under the same conditions. These efficiency improvements and the reduction of oscillations during varying wind speeds demonstrate the major achievements of the proposed algorithm

    Integration of AC/DC Microgrids into Power Grids

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    AC/DC Microgrids are a small part of low voltage distribution networks that are located far from power substations, and are interconnected through the point of common coupling to power grids. These systems are important keys for the flexible, techno-economic, and environmental-friendly generation of units for the reliable operation and cost-effective planning of smart electricity grids. Although AC/DC microgrids, with the integration of renewable energy resources and other energy systems, such as power-to-gas, combined heat and power, combined cooling heat and power, power-to-heat, power-to-vehicle, pump and compressed air storage, have several advantages, there are some technical aspects that must be addressed. This Special Issue aims to study the configuration, impacts, and prospects of AC/DC microgrids that enable enhanced solutions for intelligent and optimized electricity systems, energy storage systems, and demand-side management in power grids with an increasing share of distributed energy resources. It includes AC/DC microgrid modeling, simulation, control, operation, protection, dynamics, planning, reliability and security, as well as considering power quality improvement, load forecasting, market operations, energy conversion, cyber/physical security, supervisory and monitoring, diagnostics and prognostics systems

    Design and Control of Electrical Motor Drives

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    Dear Colleagues, I am very happy to have this Special Issue of the journal Energies on the topic of Design and Control of Electrical Motor Drives published. Electrical motor drives are widely used in the industry, automation, transportation, and home appliances. Indeed, rolling mills, machine tools, high-speed trains, subway systems, elevators, electric vehicles, air conditioners, all depend on electrical motor drives.However, the production of effective and practical motors and drives requires flexibility in the regulation of current, torque, flux, acceleration, position, and speed. Without proper modeling, drive, and control, these motor drive systems cannot function effectively.To address these issues, we need to focus on the design, modeling, drive, and control of different types of motors, such as induction motors, permanent magnet synchronous motors, brushless DC motors, DC motors, synchronous reluctance motors, switched reluctance motors, flux-switching motors, linear motors, and step motors.Therefore, relevant research topics in this field of study include modeling electrical motor drives, both in transient and in steady-state, and designing control methods based on novel control strategies (e.g., PI controllers, fuzzy logic controllers, neural network controllers, predictive controllers, adaptive controllers, nonlinear controllers, etc.), with particular attention to transient responses, load disturbances, fault tolerance, and multi-motor drive techniques. This Special Issue include original contributions regarding recent developments and ideas in motor design, motor drive, and motor control. The topics include motor design, field-oriented control, torque control, reliability improvement, advanced controllers for motor drive systems, DSP-based sensorless motor drive systems, high-performance motor drive systems, high-efficiency motor drive systems, and practical applications of motor drive systems. I want to sincerely thank authors, reviewers, and staff members for their time and efforts. Prof. Dr. Tian-Hua Liu Guest Edito

    Controle coordenado em microrredes de baixa tensão baseado no algoritmo power-based control e conversor utility interface

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    Orientadores: José Antenor Pomilio, Fernando Pinhabel MarafãoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Esta tese apresenta uma possível arquitetura e sua respectiva estratégia de controle para microrredes de baixa tensão, considerando-se a existência de geradores distribuídos pela rede. A técnica explora totalmente a capacidade dos geradores distribuídos em ambos os modos de operação: conectado à rede e ilhado. Quando conectado à rede, sob o modo de otimização global, o controle busca a operação quase ótima da microrrede, reduzindo as perdas de distribuição e os desvios de tensão. Quando em modo ilhado, a técnica regula de forma eficaz os geradores distribuídos disponíveis, garantindo a operação autônoma, segura e suave da microrrede. A estratégia de controle é aplicada a uma estrutura de microrrede completamente despachável, baseada em uma arquitetura de controle mestre-escravo, em que as unidades distribuídas são coordenadas por meio do recém-desenvolvido algoritmo Power-Based Control. As principais vantagens da arquitetura proposta são a expansividade e a capacidade de operar sem sincronização ou sem conhecimento das impedâncias de linha. Além disso, a microrrede regula as interações com a rede por meio do conversor chamado de Utility Interface, o qual é um inversor trifásico com armazenador de energia. Esta estrutura de microrrede permite algumas vantagens como: compensação de desbalanço e reativo, rápida resposta aos transitórios de carga e de rede, e suave transição entre os modos de operação. Em contrapartida, para compartilhar a potência ativa e reativa proporcionalmente entre as unidades distribuídas, controlar a circulação de reativos, e maximizar a operação, a comunicação da microrrede requer em um canal de comunicação confiável, ainda que sem grandes exigências em termos de resolução ou velocidade de transmissão. Neste sentido, foi demonstrado que uma falha na comunicação não colapsa o sistema, apenas prejudica o modo de otimização global. Entretanto, o sistema continua a operar corretamente sob o modo de otimização local, que é baseado em um algoritmo de programação linear que visa otimizar a compensação de reativos, harmônicos e desbalanço de cargas por meio dos gerador distribuído, particularmente, quando sua capacidade de potência é limitada. Esta formulação consiste em atingir melhores índices de qualidade de energia, definidos pelo lado da rede e dentro de uma região factível em termos de capacidade do conversor. Baseado nas medições de tensão e corrente de carga e uma determinada função objetiva, o algoritmo rastreia as correntes da rede ótima, as quais são utilizadas para calcular os coeficientes escalares e finalmente estes são aplicados para encontrar as referências da corrente de compensação. Finalmente, ainda é proposta uma técnica eficiente para controlar os conversores monofásicos conectados arbitrariamente ao sistema de distribuição trifásico, sejam conectados entre fase e neutro ou entre fase e fase, com o objetivo de compensar o desbalanço de carga e controlar o fluxo de potência entre as diferentes fases da microrrede. Isto melhora a qualidade da energia elétrica no ponto de acoplamento comum, melhora o perfil de tensão nas linhas, e reduz as perdas de distribuição. A arquitetura da microrrede e a estratégia de controle foi analisada e validada através de simulações computacionais e resultados experimentais, sob condições de tensão senoidal/simétrica e não-senoidal/assimétrica, avaliando-se o comportamento em regime permanente e dinâmico do sistema. O algoritmo de programação linear que visa otimizar a compensação foi analisado por meio de resultados de simulaçãoAbstract: This thesis presents a flexible and robust architecture and corresponding control strategy for modern low voltage microgrids with distributed energy resources. The strategy fully exploits the potential of distributed energy resources, under grid-connected and islanded operating modes. In grid-connected mode, under global optimization mode, the control strategy pursues quasi-optimum operation of the microgrid, so as to reduce distribution loss and voltage deviations. In islanded mode, it effectively manages any available energy source to ensure a safe and smooth autonomous operation of the microgrid. Such strategy is applied to a fully-dispatchable microgrid structure, based on a master-slave control architecture, in which the distributed units are coordinated by means of the recently developed power-based control. The main advantages of the proposed architecture are the scalability (plug-and-play) and capability to run the distributed units without synchronization or knowledge of line impedances. Moreover, the proposed microgrid topology manages promptly the interaction with the mains by means of a utility interface, which is a grid-interactive inverter equipped with energy storage. This allows a number of advantages, including compensation of load unbalance, reduction of harmonic injection, fast reaction to load and line transients, and smooth transition between operating mode. On the other hand, in order to provide demand response, proportional power sharing, reactive power control, and full utilization of distributed energy resources, the microgrid employs a reliable communication link with limited bit rate that does not involve time-critical communications among distributed units. It has been shown that a communication failure does not jeopardize the system, and just impairs the global optimization mode. However, the system keeps properly operating under the local optimization mode, which is managed by a linear algorithm in order to optimize the compensation of reactive power, harmonic distortion and load unbalance by means of distributed electronic power processors, for example, active power filters and other grid-connected inverters, especially when their capability is limited. It consists in attain several power quality performance indexes, defined at the grid side and within a feasible power region in terms of the power converter capability. Based on measured load quantities and a certain objective function, the algorithm tracks the expected optimal source currents, which are thereupon used to calculate some scaling coefficients and, therefore, the optimal compensation current references. Finally, the thesis also proposes an efficient technique to control single-phase converters, arbitrarily connected to a three-phase distribution system (line-to-neutral or line-to-line), aiming for reduce unbalance load and control the power flow among different phases. It enhances the power quality at the point-of-common-coupling of the microgrid, improve voltage profile through the lines, and reduce the overall distribution loss. The master-slave microgrid architecture has been analyzed and validated by means of computer simulations and experimental results under sinusoidal/symmetrical and nonsinusoidal/asymmetrical voltage conditions, considering both the steady-state and dynamic performances. The local optimization mode, i.e., linear algorithm for optimized compensation, has been analyzed by simulation resultsDoutoradoEnergia EletricaDoutor em Engenharia Elétrica2012/24309-8, 2013/21922-3FAPES

    Control of power converter in modern power systems

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    A la portada consta el nom del programa interuniversitari: Joint Doctoral Programme in Electric Energy Systems [by the] Universidad de Málaga, Universidad de Sevilla, Universidad del País Vasco/Euskal Erriko Unibertsitatea i Universitat Politècnica de CatalunyaPower system is undergoing an unpreceded paradigm shift: from centralized to distributed generation. As the renewable-based generations and battery storage systems are increasingly displacing conventional generations, it becomes more and. more difficult to maintain the stability and reliability of the grid by using only conventional generations. The main reason for the degradation of grid stability is the rapid penetration of nonconventional sources. These new generations interface with the grids through power electronics converters which are conventionally designed to maximize conversion efficiency and resource utilization. Indeed, these power converters only focus on their internal operation despite the grid conditions, which often worsens the grid operation. To overcome such a drawback, the grid-forming concept has been proposed for power converters, aiming to redesign the control of the power converters to enforce more grid-friendly behaviours such as inertia response and power oscillation damping to name a few. Despite the rich literature, actual adaptation of grid-forming controller in real-world applications is still rare because incentives for renewable power plants to provide services based on such advanced grid-forming functions were at best scarce. In the last years, however, several system operators have imposed new requirements and markets for grid-supporting services. In addition, the existing grid-forming controllers require modification to low-level control firmware of a power converter, which is often unrealistic due to the control hardware limitations as well as necessary testing and certifications. To ensure a stable operation of a grid-forming converter under adverse operating conditions, a robust voltage sensorless current controller is developed in this PhD thesis. The proposed controller is able to handle most of the possible abnormal conditions of the grid such as impedance variations, unbalanced voltage; harmonics distortion. These abnormalities of the grid are mathematically represented using equivalent linear models such that they can be used for calculating the controller gains. Linear matrix inequality techniques are also used to facilitate parameter tuning. In fact, the performance and stability of the current control loop can be determined through only two tuning parameters instead of eight parameters for a controller of a similar structure. The existing grid-forming implementations are designed considering that the control firmware of the power converter can be upgraded at will. However, modifications of the control firmware are not straightforward and cost-effective at mass scale. To overcome such a limitation, an external synchronous controller is presented in this PhD thesis. The external synchronous controller uses measurements, which are either provided by the power converter or a dedicated measurement unit, to calculate the actual active and reactive power that should be injected by the power converters in a way that the power plant acts as an aggregated grid­forming converter. As a result, any conventional power converters can be utilized for providing grid-supporting services with minimal modification to the existing infrastructure. Power converters can provide even better performance than a synchronous generator if a proper control scheme is used. In this regard, the final chapter of this PhD thesis presents the multi-rotor virtual machine implementation for grid-forming converter to boost their damping performance to power oscillations. The multi-rotor virtual machine-controller implements several virtual rotors instead of only one rotor as in typical grid-forming strategies. Since each of the virtual rotors is tuned to target a specific critical mode, the damping participation to such a mode can be increased and adjusted individually. The controllers presented in this PhD thesis are validated through simulators and experiments in the framework of the H2020 FlexiTranstore project. The results are throughout analysed to assess the control performance as well as to highlight possible implications.A medida que las generaciones basadas en energías renovables y los sistemas de almacenamiento de baterías desplazan la generación convencional, se vuelve cada vez más difícil mantener la estabilidad y confiabilidad de la red. Estas nuevas generaciones interactúan con las redes a través de convertidores de electrónica de potencia que están diseñados tradicionalmente para maximizar la eficiencia de conversión y la utilización de recursos. Estos convertidores centran su funcionamiento interno independientemente de las condiciones de la red, lo que a menudo empeora el funcionamiento de la red. Para esto, se ha propuesto el concepto de convertidores de potencia formadores de red (grid-forming), con el objetivo de rediseñar el control de los convertidores de potencia para imponer comportamientos más favorables a la red, por ejemplo, la respuesta inercial y la amortiguación de oscilaciones de potencia. No en tanto, la adaptación real del controlador grid-forming en aplicaciones del mundo real todavía es escasa debido a los pocos incentivos para que las plantas de energía renovable proporcionen servicios basados en funciones de formación de red tan avanzadas. Aunque en los últimos años, operadores de sistemas han impuesto nuevos requisitos y mercados para servicios auxiliares, los controladores grid-forming existentes requieren cambios en el firmware de control de bajo nivel de un convertidor de potencia, algo poco realista debido a las limitaciones del hardware de control, así como a las pruebas y certificaciones necesarias. En esta tesis se desarrolla un controlador de corriente robusto, sin sensor de tensión, para garantizar el funcionamiento estable de un convertidor grid-forming en condiciones de operación adversas. Este controlador es capaz de manejar la mayoría de las condiciones anormales de red, como variaciones de impedancia, tensión desequilibrada y distorsión de armónicos. Estas anomalías de la red se representan matemáticamente mediante modelos lineales equivalentes, utilizados para calcular las ganancias del controlador. También, usando técnicas de desigualdad matricial lineal para facilitar el ajuste de parámetros. De hecho, el rendimiento y la estabilidad del bucle de control de la corriente pueden determinarse mediante sólo dos parámetros de sintonización. Las implementaciones de formación de red existentes están diseñadas considerando que el firmware de control del convertidor de potencia puede actualizarse a voluntad. Sin embargo, las modificaciones del firmware de control no son sencillas ni rentables a gran escala. Por tanto, esta tesis presenta un controlador síncrono externo que utiliza las mediciones proporcionadas por el convertidor de potencia o por una unidad de medición dedicada para calcular la potencia activa y reactiva real que deben inyectar los convertidores de potencia, de forma que la central eléctrica actúe como un convertidor grid-forming agregado. Como resultado, cualquier convertidor de potencia convencional puede utilizarse para proporcionar servicios de apoyo a la red con una modificación mínima de la infraestructura existente. Los convertidores de potencia pueden ofrecer mejor rendimiento que un generador síncrono utilizando un esquema de control adecuado. El último capítulo de esta tesis presenta la implementación de una máquina virtual multirrotor para que los convertidores de red aumenten su rendimiento de amortiguación de las oscilaciones de potencia. El controlador de la máquina virtual multirrotor implementa varios rotores virtuales en lugar de un solo rotor como en las estrategias típicas de grid-forming. Dado que cada uno de los rotores virtuales está sintonizado para dirigirse a un modo crítico específico, la participación de la amortiguación a dicho modo puede aumentarse y ajustarse individualmente. Los controladores presentados en esta tesis doctoral han sido validados mediante simulaciones y experimentos en el marco del proyecto H2020 FlexiTranstore.Postprint (published version

    PV System Design and Performance

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    Photovoltaic solar energy technology (PV) has been developing rapidly in the past decades, leading to a multi-billion-dollar global market. It is of paramount importance that PV systems function properly, which requires the generation of expected energy both for small-scale systems that consist of a few solar modules and for very large-scale systems containing millions of modules. This book increases the understanding of the issues relevant to PV system design and correlated performance; moreover, it contains research from scholars across the globe in the fields of data analysis and data mapping for the optimal performance of PV systems, faults analysis, various causes for energy loss, and design and integration issues. The chapters in this book demonstrate the importance of designing and properly monitoring photovoltaic systems in the field in order to ensure continued good performance
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