Active power sharing and frequency regulation in inverter-based islanded microgrids subject to clock drifts, damage in power links and loss of communications

Tesi en modalitat de compendi de publicacions; hi ha diferents seccions retallades per drets de l'editorMicrogrids (MGs) are small-scale power systems containing storage elements, loads and distributed generators that are interfaced with the electric network via power electronic inverters. When an MG is in islanded mode, its dynamics are no longer dominated by the main grid. Then, inverters, driven by digital processors that may exchange data over digital communication, must act as voltage source inverters (VSIs) to take coordinated actions to ensure power quality and supply. The scope of this thesis is bounded to control strategies for active power sharing and frequency regulation in islanded MGs. The focus is on the analysis of prototype control policies when operating conditions are no longer ideal. In particular, the thesis covers the effect that a) clock drifts of digital processors, b) damage in power transmission lines, and c) failures in digital communications have in control performance. The work is submitted as a compendium of publications, including journal and international conference papers, where two main areas of research can be distinguished. The first area refers to the analysis of the effect that clock drifts have on frequency regulation and active power sharing. VSIs digital processors are equipped with oscillators, which run at not necessarily identical frequencies. As consequence, the local clocks in the physically distributed VSIs may differ. This part, reported in two conference papers and one journal paper, investigates state-of-the-art control policies when clocks of the computational devices drift. The contributions related to this part are a) the reformulation of existing control policies in terms of clock drifts, b) the steady-state analysis of these policies that offers analytical expressions to quantify the impact that drifts have on frequency and active power equilibrium points, c) the closed-loop model capable of accommodating all the policies, d) the stability analysis of the equilibrium points, and e) the experimental results. The second area copes with the analysis of the effect that electrical and communication failures have on frequency regulation and active power sharing. This investigation focuses on distributed/cooperative control policies where each inverter control action is computed using both local measures and data received from other inverters within the MG. This part, reported in one conference paper and two journal papers, investigates two control policies when the considered failures in terms of damage in power links and/or loss of communication between inverters provoke partitions within the MG. The contributions related to this part are a) the formulation of the MG as two connected graphs corresponding to the electrical and communication networks where both type of failures lead to disconnected electrical/communication sub-graphs, named partitions, that co-exist within the MG, b) the closed-loop model integrating the two graph Laplacian matrices, c) the stability analysis that identifies which type of partitions may lead to MG instability, d) the steady-state analysis that indicates how to compute the equilibrium points for the case of stable dynamics, e) a new control strategy based on switched control principles that permits avoiding the instability scenario, and f) the experimental results. For the purpose of verifying the operational performance of the analytical results, diverse experiments on a laboratory MG have been performed. The outcomes obtained are discussed and analyzed in terms of the objectives sought. Finally, conclusions and future research lines complete the thesis.Las microredes (MG) son sistemas de energía a pequeña escala que contienen elementos de almacenamiento, cargas y generadores distribuidos que están conectados con la red eléctrica a través de inversores de potencia. Cuando una MG está en modo aislado, su dinámica no está dominada por la red principal. Así, los inversores, comandados por procesadores digitales que pueden intercambiar información a través de comunicaciones digitales, deben actuar como fuentes de voltaje para ejecutar acciones coordinadas que garanticen el suministro de energía. Esta tesis se enmarca dentro de estrategias de control de última generación para compartir potencia activa y regular frecuencia en MG aisladas basadas en inversores. Su enfoque se centra en analizar estas políticas cuando las condiciones de operación no son ideales. En particular, la tesis cubre el efecto que a) desviaciones del reloj de los procesadores digitales, b) daños en las líneas de transmisión de energía, y c) fallas en las comunicaciones digitales, provocan en el rendimiento de control. El trabajo se presenta como un compendio que incluye publicaciones de revistas y de conferencias internacionales, donde se pueden distinguir dos temas principales de investigación. El primer tema comprende el análisis del efecto que tienen las desviaciones de reloj sobre la regulación de frecuencia y la compartición de potencia activa. Los procesadores de los inversores están equipados con osciladores que funcionan a frecuencias no necesariamente idénticas. Como consecuencia, los relojes locales en los inversores distribuidos físicamente, pueden diferir. Esta parte, descrita a través de dos artículos de conferencia y uno de revista, analiza el comportamiento de las políticas de control cuando los relojes de los dispositivos computacionales se desvían. Las contribuciones relacionadas con este tema son a) reformulación de las políticas de control de última generación en términos de desviaciones de reloj, b) análisis de estado estacionario de estas estrategias que ofrece expresiones analíticas para cuantificar el impacto que las desviaciones de reloj tienen sobre los puntos de equilibrio de frecuencia y potencia activa, c) modelo de lazo cerrado adaptable a todas las políticas, d) análisis de estabilidad de los puntos de equilibrio, y e) resultados experimentales. El segundo tema hace frente al análisis del efecto que las fallas eléctricas y de comunicaciones tienen sobre la regulación de frecuencia y el uso compartido de potencia activa. Esta parte se centra en políticas de control distribuido/cooperativo donde cada acción de control del inversor se calcula utilizando medidas locales y datos recibidos de otros inversores de la MG. Esta parte, descrita a través de un artículo de conferencia y dos de revista, investiga dos políticas de control cuando particiones en la MG son provocadas por daños en los enlaces de alimentación y/o por pérdida de comunicación entre inversores. Las contribuciones relacionadas con este tema son a) formulación de la MG como dos grafos correspondientes a las redes eléctrica y de comunicación donde ambos tipos de fallas conducen a sub-grafos eléctricos/comunicacionales desconectados, llamados particiones, que coexisten dentro de la MG, b) modelo de lazo cerrado que integra las matrices Laplacianas de los dos grafos, c) análisis de estabilidad que identifica las particiones que pueden conducir a inestabilidad en la MG, d) análisis de estado estacionario para calcular puntos de equilibrio cuando la dinámica es estable, e) nueva estrategia basada en principios de control conmutado para evitar el escenario de inestabilidad, y f) resultados experimentales. Con el fin de verificar el rendimiento operativo de los resultados analíticos, se han realizado diversos experimentos sobre una microred de laboratorio, los mismos que se discuten en términos de los objetivos de la tesis. El trabajo finaliza con las conclusionesPostprint (published version

A Comprehensive Review of Control Strategies and Optimization Methods for Individual and Community Microgrids

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Community Microgrid offers effective energy harvesting from distributed energy resources and efficient energy consumption by employing an energy management system (EMS). Therefore, the collaborative microgrids are essentially required to apply an EMS, underlying an operative control strategy in order to provide an efficient system. An EMS is apt to optimize the operation of microgrids from several points of view. Optimal production planning, optimal demand-side management, fuel and emission constraints, the revenue of trading spinning and non-spinning reserve capacity can effectively be managed by EMS. Consequently, the importance of optimization is explicit in microgrid applications. In this paper, the most common control strategies in the microgrid community with potential pros and cons are analyzed. Moreover, a comprehensive review of single objective and multi-objective optimization methods is performed by considering the practical and technical constraints, uncertainty, and intermittency of renewable energies sources. The Pareto-optimal solution as the most popular multi-objective optimization approach is investigated for the advanced optimization algorithms. Eventually, feature selection and neural network-based clustering algorithms in order to analyze the Pareto-optimal set are introduced.This work was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN)–Agencia Estatal de Investigación (AEI), and by the European Regional Development Funds (ERDF), a way of making Europe, under Grant PGC2018-098946-B-I00 funded by MCIN/AEI/10.13039/501100011033/.Peer ReviewedPostprint (published version

Robust, Resilient and Reliable Architecture for V2X Communication

The new developments in mobile edge computing (MEC) and vehicle-to-everything (V2X) communications has positioned 5G and beyond in a strong position to answer the market need towards future emerging intelligent transportation systems and smart city applications. The major attractive features of V2X communication is the inherent ability to adapt to any type of network, device, or data, and to ensure robustness, resilience and reliability of the network, which is challenging to realize. In this work, we propose to drive these further these features by proposing a novel robust, resilient and reliable architecture for V2X communication based on harnessing MEC and blockchain technology. A three stage computing service is proposed. Firstly, a hierarchcial computing architecture is deployed spanning over the vehicular network that constitutes cloud computing (CC), edge computing (EC), fog computing (FC) nodes. The resources and data bases can migrate from the high capacity cloud services (furthest away from the individual node of the network) to the edge (medium) and low level fog node, according to computing service requirements. Secondly, the resource allocation filters the data according to its significance, and rank the nodes according to their usability, and selects the network technology according to their physical channel characteristics. Thirdly, we propose a blockchain-based transaction service that ensures reliability. We discussed two use cases for experimental analysis, plug- in electric vehicles in smart grid scenarios, and massive IoT data services for autonomous cars. The results show that car connectivity prediction is accurate 98% of the times, where 92% more data blocks are added using micro-blockchain solution compared to the public blockchain, where it is able to reduce the time to sign and compute the proof-of-work (PoW), and deliver a low-overhead Proof-of-Stake (PoS) consensus mechanism. This approach can be considered a strong candidate architecture for future V2X, and with more general application for everything- to-everything (X2X) communications