Grupo de Sistemas Electrónicos Industriales
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Experimental Study of a Centralized Control Strategy of a DC Microgrid Working in Grid Connected Mode
[EN] The results concerning the integration of a set of power management strategies and serial communications for the efficient coordination of the power converters composing an experimental DC microgrid is presented. The DC microgrid operates in grid connected mode by means of an interlinking converter. The overall control is carried out by means of a centralized microgrid controller implemented on a Texas Instruments TMS320F28335 DSP. The main objectives of the applied control strategies are to ensure the extract/inject power limits established by the grid operator as well as the renewable generation limits if it is required; to devise a realistic charging procedure of the energy storage batteries as a function of the microgrid status; to manage sudden changes of the available power from the photovoltaic energy sources, of the load power demand and of the power references established by the central controller; and to implement a load shedding functionality. The experimental results demonstrate that the proposed power management methodology allows the control of the power dispatch inside the DC microgrid properly.
Concepción e integración de arquitecturas y protocolos de comunicación dentro de sistemas de supervisión y control de microrredes inteligentes
[ES] Las microrredes inteligentes se presentan como una solución para integrar las energías renovables así como para mejorar la eficiencia de la red por medio de la incorporación de las Tecnologías de Información y Comunicación (TIC). Sin embargo, la alta penetración de los recursos energéticos distribuidos (RED) en las microrredes, requiere una serie de cambios técnicos en los sistemas de comunicación caracterizados tradicionalmente por esquemas centralizados, donde un controlador central se comunica con todos los recursos energéticos distribuidos y toma decisiones, hacia esquemas descentralizados donde cada recurso energético distribuido tiene capacidad de comunicación y decisión de forma local. En este sentido, el objetivo global de las estrategias de comunicación descentralizadas es dotar al sistema energético de una mayor escalabilidad, fiabilidad, robustez, y flexibilidad que la que presentan los sistemas centralizados. Además, las microrredes con esquemas descentralizados presentan una gran oportunidad para el advenimiento del futuro Internet de la Energía o Internet of Energy (IoE), ya que cada recurso energético distribuido desplegado en la microrred es susceptible de conectarse a la nube y enviar y recibir datos desde hacia la red en tiempo real, en cualquier momento y lugar. Uno de los puntos críticos derivados de la incorporación de las TIC en las microrredes de gestión distribuida es garantizar la conectividad entre los recursos energéticos al tiempo que se satisfacen los requisitos técnicos de estos sistemas energéticos. Los distintos estándares y normas establecidas para el despliegue de microrredes destacan la necesidad de cumplir con algunos parámetros de calidad de servicio (Quality of Service, QoS) como ancho de banda, latencias, throughput (rendimiento), entre otros, ya que un ancho de banda bajo puede dar lugar a cuellos de botella, pérdida de paquetes de datos y distorsión. Por otra parte, si la comunicación no presenta una tasa positiva de promedio de éxito o sufre retardos y/o supera el tiempo requerido, la información no cumple su cometido y, en el peor de los casos, daños eléctricos se pueden producir en la microrred. En la presente tesis se presenta el diseño, desarrollo e implementación de infraestructuras de comunicación distribuidas para la gestión, monitorización y control de microrredes que permitan administrar la potencia y energía eficientemente mediante comunicaciones síncronas y asíncronas. Además, este estudio describe las principales características de la Internet de la Energía, los principios en los que se basa, los elementos y tecnologías disponibles para lograr la comunicación entre los recursos distribuidos desplegados en la microrred y establece las principales diferencias de IoE con respecto a los sistemas tradicionales de monitoreo y gestión. Con toda esta información, se describe una propuesta de arquitectura de la Internet de la Energía aplicada a las microrredes y un prototipo de monitoreo y gestión. Se han realizado ensayos experimentales para validar los estudios y propuestas realizadas. Para ello se ha desplegado una red Ethernet en la microrred experimental del Grupo de Sistemas Electrónicos Industriales (GSEI) y se ha dotado a cada recurso energético distribuido de capacidades de comunicación e inteligencia a través del acoplamiento de sistemas de placa única BeagleBone Black donde poder instaurar el software desarrollado. Los resultados han evidenciado que las arquitecturas de comunicación distribuida propuestas permiten comunicaciones robustas, eficientes, escalables y flexibles en el ámbito de las microrredes a la vez que se cumplen con los requerimientos técnicos demandados por éstas.
Practical Analysis and Design of a Battery Management System for a Grid-Connected DC Microgrid for the Reduction of the Tariff Cost and Battery Life Maximization
[EN] This study is focused on two areas: the design of a Battery Energy Storage System(BESS) for a grid-connected DC Microgrid and the power management of that microgrid. The power management is performed by a Microgrid Central Controller (MGCC). A Microgrid operator provides daily information to the MGCC about the photovoltaic generation profile, the load demand profile, and the real-time prices of the electricity in order to plan the power interchange between the BESS and the main grid, establishing the desired state of charge (SOC) of the batteries at any time. The main goals of the power management strategy under study are to minimize the cost of the electricity that is imported from the grid and to maximize battery life by means of an adequate charging procedure, which sets the charging rate as a function of the MG state. Experimental and simulation results in many realistic scenarios demonstrate that the proposed methodology achieves a proper power management of the DC microgrid.
Power Management of the DC Bus Connected Converters in a Hybrid AC/DC Microgrid Tied to the Main Grid
[EN] In this paper, a centralized control strategy for the efficient power management of power converters composing a hybrid AC/DC microgrid is explained. The study is focused on the converters connected to the DC bus. The proposed power management algorithm is implemented in a microgrid central processor which is based on assigning several operation functions to each of the generators, loads and energy storage systems in the microgrid. The power flows between the DC and AC buses are studied in several operational scenarios to verify the proposed control. Experimental and simulation results demonstrate that the algorithm allows control of the power dispatch inside the microgrid properly by performing the following tasks: communication among power converters, the grid operator and loads; connection and disconnection of loads; control of the power exchange between the distributed generators and the energy storage system and, finally, supervision of the power dispatch limit set by the grid operator.
Efficient Event Notification Middleware for Smart Microgrids over P2P Networks
[EN] Microgrids are moving towards large-scale smart distributed networks which demand an efficient and reliable communication infrastructure to manage, control and monitor energy resources. With regard to this, publisher/subscriber eventbased middleware has become relevant for large-scale distributed time applications because it allows decouple time and space between senders and receivers. Particularly the content publish/subscribe systems over structured peer-to-peer (P2P) networks has emerged to enhance scalability and dynamism of notification middleware systems. However, this type of systems use multicast routing schemes that still generate much network traffic and as a consequence an overload of the communication channel is produced. This results in inefficient network utilization and rapid depletion of network resources leading to unreliable operations, degradation of system performance and even instability of the microgrid. In this paper, a new content-based publish/subscribe notification middleware over structured P2P systems is proposed, such that smart microgrid communication requirements are met. This proposed system organizes the publications and subscriptions in a one dimensional representation using the Hilbert space filling curve. Through this representation, an innovative routing and matching algorithms are developed. Experimental results demonstrate that the proposed publisher/subscribe system significantly enhance efficiency of the system, network performance and the use of computational resources.
Diseño, Desarrollo e Implementación de una Infraestructura de Comunicación P2P para el Control y Monitorización de Microrredes Inteligentes
[EN] The concept of Microgrid has emerged as a feasible answer to the challenges raised by the increasing introduction of Distributed Energy Resources (DERs) and Renewable Energy Sources (RES) into the electrical grid towards a more active, flexible, efficient and environmental alternative to consider a set of various microgeneration together with storage and loads units as a system that can be operated in a non-autonomous way, if interconnected to the grid, or in an autonomous way, if disconnected from the main grid. From the technological point of view, guaranteeing, highly and bidirectional connectivity between microgrid resources, reliable communications and seamless integration of multiple devices are mandatory in a microgrid. Therefore, the aim of this project is design, development and implementation, on an experimental microgrid, of a communication infrastructure that enables an optimal, safe and reliable execution of microgrid hierarchical control levels to optimize power flows inside itself.
An Algorithm for the Efficient Management of the Power Converters Connected to the DC Bus of a Hybrid Microgrid Operating in Grid-connection Mode
[EN] In this paper a centralized control strategy for the efficient power management of the power converters conforming a hybrid distributed generation microgrid is explained. The microgrid is based on a DC and an AC bus. The study is focused on the converters connected to the DC bus. The proposed power management algorithm is implemented in a microgrid central processor. This algorithm is based on assigning several operation functions to each of the generators, loads and energy storage systems in the microgrid. A communication system is used to assign the operation functions to each of the microgrid elements. The power flows between the DC and AC buses are studied in several operation scenarios, in which the proposed control can be verified. Experimental and simulation results demonstrate that the algorithm allows to control the power dispatch inside the microgrid properly, by performing the following tasks: (1) the communications among power converters, the grid operator and intelligent loads, (2) the connection and disconnection of loads, (3) the control of the power exchange between the distributed generators and the energy storage system, (4) the compliance of the power dispatch limit set by the grid operator, (5) the synchronization with the grid and (6) the control of the voltage at the DC bus.
Current challenges and future trends in the field of communication architectures for microgrids
[EN] The concept of microgrid has emerged as a feasible answer to cope with the increasing number of distributed renewable energy sources which are being introduced into the electrical grid. The microgrid communication network should guarantee a complete and bidirectional connectivity among the microgrid resources, a high reliability and a feasible interoperability. This is in a contrast to the current electrical grid structure which is characterized by the lack of connectivity, being a centralized-unidirectional system. In this paper a review of the microgrids information and communication technologies (ICT) is shown. In addition, a guideline for the transition from the current communication systems to the future generation of microgrid communications is provided. This paper contains a systematic review of the most suitable communication network topologies, technologies and protocols for smart microgrids. It is concluded that a new generation of peer-to-peer communication systems is required towards a dynamic smart microgrid. Potential future research about communications of the next microgrid generation is also identified.
A Novel Locality Algorithm and Peer-to-Peer Communication Infrastructure for Optimizing Network Performance in Smart Microgrids
[EN] Peer-to-Peer (P2P) overlay communications networks have emerged as a new paradigm for implementing distributed services in microgrids due to their potential benefits: they are robust, scalable, fault-tolerant, and they can route messages even with a large number of nodes which are frequently entering or leaving from the network. However, current P2P systems have been mainly developed for file sharing or cycle sharing applications where the processes of searching and managing resources are not optimized. Locality algorithms have gained a lot of attention due to their potential to provide an optimized path to groups with similar interests for routing messages in order to get better network performance. This paper develops a fully functional decentralized communication architecture with a new P2P locality algorithm and a specific protocol for monitoring and control of microgrids. Experimental results show that the proposed locality algorithm reduces the number of lookup messages and the lookup delay time. Moreover, the proposed communication architecture heavily depends of the lookup used algorithm as well as the placement of the communication layers within the architecture. Experimental results will show that the proposed techniques meet the network requirements of smart microgrids even with a large number of nodes on stream.
Synchronization of power inverters in islanded microgrids using an FM-modulated signal
A microgrid can operate in island mode, isolated from the main grid during certain time intervals. When operated in island mode, the electronic converters of the microgrid must keep the voltage and frequency of the microgrid inside the desired range. The converters of a microgrid can be classified into three groups: 1) grid-feeding; 2) grid-supporting; and 3) grid-forming power converters. The grid-forming converters operate as a voltage source, and require an external synchronization signal provided by the microgrid central controller. Both the noise and the delay in the synchronization signals received by the grid-forming converters are critical issues, which deteriorate the quality of the microgrid voltage and may overload those converters. The synchronization signals must be robust and suitable for operating in noisy environments. In this paper, the synchronization signal is frequency-modulated to be transmitted, being robust against noise. The transmission is done through an industrial RS-485 line with a low delay. The demodulation is performed with a low computational load by the control processors of the grid-forming power converters.