Search

Microgrids (MG) are exposed to voltage quality deterioration due to the presence of voltage unbalance. To deal with this problem, existing solutions based on Distributed Generation (DG) units interfaced by power electronics offer two type of strategies for voltage unbalance compensation depending on whether the compensation is performed at one remote node or at multiple local nodes. The first type is limited to a single node, and the second type is limited to apply at the DG units output (locally). This paper presents a multi nodal control scheme where DGs can compensate for voltage unbalance at multiple remote nodes of the MG, thus overcoming both state-of-the-art strategies limitations. In particular, negative-sequence voltage is eliminated at as many remote nodes as the number of available DG's. A systematic approach for the multiple-input/multiple-output (MIMO) nature of the problem is presented covering three aspects. First, a square MIMO control strategy is established and a feasibility test is derived to assess whether the problem can be solved. Second, the cross-coupling interaction between the multiple controllers is minimized by optimally selecting which DGs will contribute to mitigate the remote unbalances. Third, stability and transient dynamics are analyzed. Laboratory experimental results corroborate the control performance., This work was supported by I+D+i PID2021-122835OB-C21 research project, financed by MCIN/AEI/10.13039/501000011033 and FEDER “Una manera de hacer Europa., Peer Reviewed, Postprint (author's final draft)

Títol diferent emprat a la intranet docent de l'EPSEVG: "Estudio del contenido armónico de la tensión de salida de un inversor trifásico conectado a la red eléctrica", Aquesta investigació es va centrar en l'anàlisi i estudi dels harmònics generats a la xarxa utilitzant mètodes de control avançats com el SOGI, amb l'objectiu de comparar diferents casos i desenvolupar conclusions basades en els resultats obtinguts a les simulacions i proves, per intentar mitigar i oferir una resposta a la degradació en el seguiment dels paràmetres de la xarxa. Aquest treball presenta un mètode de sincronització en freqüència multiresonant per a dispositius connectats a la xarxa, que permet estimar no només les components de seqüència positiva i negativa de la senyal a la freqüència fonamental, sinó també en altres components de seqüència harmònica. El sistema proposat es diu MDSOGI ja que es basa en una xarxa de desacoblament harmònic que consta de múltiples integradors generalitzats de segon ordre (MSOGI). En aquest treball s'analitza el MDSOGI per a aplicacions trifàsiques, deduint algunes expressions clau respecte a la seva estabilitat i sintonització. A més, el rendiment del MDSOGI s'avalua mitjançant simulacions per mostrar la seva capacitat per detectar diferents components harmòniques en diferents tipus d'escenaris a la xarxa, mitjançant la implementació de diferents tipus de càrregues., Esta investigación se enfocó en el análisis y estudio de los armónicos generados en la red utilizando métodos de control avanzados como el SOGI, con el objetivo de comparar distintos casos y desarrollar conclusiones en base a los resultados obtenidos en las simulaciones y testeos, para intentar mitigar y ofrecer una respuesta a la degradación en el seguimiento de los parámetros de la red. Este trabajo presenta un método de sincronización en frecuencia multirresonante para dispositivos conectados a red, que permite estimar no sólo las componentes de secuencia positiva y negativa de la señal en la frecuencia fundamental, sino también en otras componentes de secuencia armónica. El sistema propuesto se llama MDSOGI ya que se basa en una red de desacoplamiento armónico que consta de múltiples integradores generalizados de segundo orden (MSOGI). En este trabajo se analiza el MDSOGI para aplicaciones trifásicas, deduciendo algunas expresiones clave respecto a su estabilidad y sintonización. Además, el rendimiento del MDSOGI se evalúa mediante simulaciones para mostrar su capacidad para detectar diferentes componentes armónicas en diferentes tipos de escenarios en la red, mediante la implementación de distintos tipos de cargas., This research focused on the analysis and study of harmonics generated in the network using advanced control methods such as SOGI, with the aim of comparing different cases and drawing conclusions based on the results obtained in simulations and testing. The goal was to attempt to mitigate and provide a response to the degradation in tracking network parameters. This work introduces a multiresonant frequency synchronization method for network-connected devices, allowing for the estimation of not only the positive and negative sequence components of the signal at the fundamental frequency, but also at other harmonic sequence components. The proposed system is called MDSOGI, as it is based on a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGI). The MDSOGI is analysed for three-phase applications in this work, deducing key expressions regarding its stability and tuning. Furthermore, the performance of the MDSOGI is evaluated through simulations to demonstrate its capability to detect different harmonic components in various network scenarios by implementing different types of loads.

© 2023 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., During voltage sags, three-phase three-wire power inverters can provide voltage support with several current injection strategies. In general, good results are ob- tained, except in overvoltage situations when one or more phase voltages exceed the allowed limit in grid codes. In three-wire inverters, this is a challenging problem because phase voltages are coupled. In this article, we present a strategy that performs independent reactive current injec- tion for each phase, which solves the overvoltage problem. This approach also includes a current-limiting technique that guarantees the injection of the maximum active power under safe current conditions. A stability analysis is carried out based on the small-gain theorem. The properties of the proposed control are experimentally validated with selected tests in a laboratory setup. A performance comparison with state-of-the-art control strategies is also included in the experimental validation., Postprint (published version)

El desenvolupament de vehicles elèctrics amb arquitectura de 800V representa un avenç significatiu a la indústria automotriu, optimitzant la càrrega ràpida i la eficiència energètica. Aquest treball explora les estratègies utilitzades per els fabricants per adaptar les tensions de càrrega de 500V fins a la tensió de 800V de les bateries. Mitjançant un projecte de benchmarking realitzat a l’empresa Applus+ IDIADA, s’analitzen quatre vehicles 100% elèctrics (Porsche Taycan, BYD HAN, Hyundai IONIQ6 i Hummer), amb els quals s’analitza l’eficiència del convertidor elevador intern comparant els ripples durant la càrrega. Els resultats mostren que mentre els sistemes de BYD i Hyundai presenten nivells alts de ripple, el sistema de Porsche en genera menys, oferint la millor eficiència però amb alguna limitació per carregar a màxima potència amb estacions de càrrega de 500V. El sistema de càrrega del Hummer, tot i no generar ripple, mostra alguna limitació al carregar a màxima potència com el Porsche. Aquest estudi remarca la importància de seleccionar una estratègia de càrrega que equilibri eficàcia, cost i adaptabilitat., El desarrollo de vehículos eléctricos con arquitectura de 800V representa un avance significativo en la industria automotriz, optimizando la carga rápida y la eficiencia energética. Este trabajo explora las estrategias utilizadas por los fabricantes para adaptar las tensiones de carga de 500V hasta la tensión de 800V de las baterías. Mediante un proyecto de benchmarking realizado en la empresa Applus+ IDIADA, se analizan cuatro vehículos 100% eléctricos (Porsche Taycan, BYD HAN, Hyundai IONIQ6 y Hummer), con los cuales se analiza la eficiencia del convertidor elevador interno comparando los ripples durante la carga. Los resultados muestran que mientras los sistemas de BYD y Hyundai presentan niveles altos de ripple, el sistema de Porsche genera menos, ofreciendo la mejor eficiencia pero con alguna limitación para cargar a máxima potencia con estaciones de carga de 500V. El sistema de carga del Hummer, a pesar de no generar ripple, muestra alguna limitación al cargar a máxima potencia como el Porsche. Este estudio subraya la importancia de seleccionar una estrategia de carga que equilibre eficacia, costo y adaptabilidad., The development of electric vehicles with 800V architecture represents a significant advancement in Automotive industry, optimizing rapid charging and energy efficiency. This study explores the strategies used by manufacturers to adapt the charging voltages from 500V to the 800V battery voltage. Through a benchmarking project conducted at Applus+ IDIADA, four 100% electric vehicles (Porsche Taycan, BYD HAN, Hyundai IONIQ6 and Hummer) are tested, examining the efficency of the internal boost converter by comparing the ripple during charging. The results show that the BYD and Hyundai systems exhibit high levels of ripple, the Porsche System generates less, offering the best efficiency but with some limitations when charging at màximum power with 500V charging stations . The Hummer’s charging System, although not generating ripple, shows some limitations when Charging at maximum power like the Porsche. This study highlights the importance of selecting a charging strategy that balances effectiveness, cost and adaptability.

Con el rápido desarrollo de la tecnología moderna de electrónica de potencia, varios dispositivos electrónicos de potencia se utilizan ampliamente en diversos campos, como los sistemas de energía, la industria y el transporte, etc. Sin embargo, dado que los dispositivos electrónicos de potencia son un tipo de carga topológica no lineal variable en el tiempo, los armónicos y la potencia reactiva generados por ellos se inyectan en la red eléctrica, lo que aumentará la capacidad de los equipos y la pérdida de línea, provocará una disminución de la utilización de los equipos de generación y distribución de energía, afectará a la calidad del suministro eléctrico y supondrá una amenaza potencial para el funcionamiento seguro y estable del sistema eléctrico. Constituye una amenaza potencial para el funcionamiento seguro y estable del sistema eléctrico. En la actualidad, la contaminación armónica, las interferencias electromagnéticas y la reducción del factor de potencia se han convertido en las tres principales molestias del sistema eléctrico público, por lo que es de gran importancia práctica estudiar y analizar las causas de la generación de armónicos, proporcionar un buen método de detección para suprimir las interferencias armónicas en el sistema eléctrico y mejorar la calidad del funcionamiento de la red eléctrica. Se utiliza un método de detección de sincronización adaptable a la frecuencia para garantizar que la salida del convertidor de potencia se sincroniza con la red cuando ésta presenta condiciones como desequilibrio de tensión trifásica o contiene armónicos de baja frecuencia. El método se basa en una red de desacoplamiento basada en múltiples integradores generalizados de segundo orden, y la separación de las componentes fundamental y armónica se consigue mediante filtros equivalentes. El método puede detectar las componentes de secuencia positiva y negativa de la señal de potencia en la frecuencia fundamental, y también es adecuado para detectar las componen, With the rapid development of modern power electronics technology, various power electronic devices are widely used in various fields, such as power systems, industry and transportation, etc. However, since power electronic devices are a kind of non-linear timevarying topological load, the harmonics and reactive power generated by them are injected into the power grid, which will increase the equipment capacity and line loss, cause a decrease in the utilization of power generation and distribution equipment, affect the quality of power supply, and pose a potential threat to the safe and stable operation of the power system. At present, harmonic pollution, electromagnetic interference and power factor reduction have become the three major nuisances in the public power system, so it is of great practical importance to study and analyze the causes of harmonic generation, provide a good detection method to suppress harmonic interference in the power system and improve the quality of power grid operation. A frequency adaptive synchronization detection method is used to ensure that the output of the power converter is synchronized with the grid when the grid exhibits conditions such as three-phase voltage unbalance or contains low-frequency harmonics. The method is based on a decoupling network based on multiple generalized second-order integrators, and separation of the fundamental and harmonic components is achieved by equivalent filters. The method can detect the positive and negative sequence components of the power signal at the fundamental frequency, and is also suitable for detecting the continuous components of multiple harmonics. Theoretical analysis and Matlab simulations show that the frequency-adaptive synchronous detection method can effectively obtain the phase and amplitude of the positive and negative sequence components of harmonics under grid-fault conditions, and has good static and dynamic performance. In this work, the definition of harmonics and the

© 2024 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., Grid-connected ac microgrids (MG) are commonly exposed to voltage quality deterioration due to the presence of voltage imbalance. This article presents a control strategy that enables MG grid-feeding inverters (interfacing distributed generation units) to compensate for the voltage unbalance at a given remote node of the MG where for example a sensitive load is likely to be damaged. Each inverter is equipped with a new controller whose operation 1) allows to contribute in the control of the imbalance by only using a measure of the negative-sequence voltage at the remote node while 2) ensuring a fairly redistribution of the control effort among the participating inverters in terms of an inherent negative-sequence current sharing functionality. Since both control objectives are achieved without requiring the collaboration among the participating inverters, the presented solution offers an inherent robustness not found in previous state-of-the-art voltage unbalance control strategies. The new control strategy is accompanied by a controller parameter design receipt, and it is complemented by a formal analysis that permits evaluating how MG modeling errors and uncertainties affect stability and performance. Laboratory experimental results corroborate the properties of the presented control., This work was supported in part by the I+D+i PID2021-122835OB-C21 research project, financed by MCIN/AEI/10.13039/501000011033 and in part by the FEDER “Una manera de hacer Europa.”, Peer Reviewed, Postprint (author's final draft)

This article presents a new switching strategy for a unity power factor rectifier (UPFR) using sliding-mode control (SMC). The traditional SMC in the natural frame suffers from a cross-coupling problem among controllers due to the neutral point voltage. To address this issue, a nonlinear transformation is applied to obtain the voltages and currents in a new 2-D reference frame. Based on the transformed variables, a nonlinear model is derived, and two different sliding-mode surfaces are designed using hysteresis band comparators. The nonlinear transformation is based on a switching strategy that not only avoids the cross-coupling problem but also injects a third harmonic in the control signal, providing an extended control range. As a result, a SMC is designed, providing relevant properties such as output voltage robustness, fast transient response against sudden load changes, and grid-voltage sags. Experimental results are provided to validate the theoretical contributions of this article., This work was supported in part by I+D+i PID2021-122835OB-C21 research project through MCIN/AEI/ 10.13039/501000011033 and FEDER “Una manera de hacer Europa.”, Peer Reviewed, Postprint (published version)

En el contexto de la creciente integración de fuentes de energía renovable en las redes eléctricas, los inversores conectados a la red juegan un papel crucial. Sin embargo, uno de los desafíos más significativos asociados con estos dispositivos es la presencia de componentes de voltaje desbalanceados en el punto de acoplamiento común (PCC), especialmente el voltaje de secuencia negativa. Este fenómeno puede afectar negativamente la calidad de la energía y la estabilidad del sistema. Esta investigación se centra en el análisis y la reducción del voltaje de secuencia negativa en la salida de los inversores conectados a la red para mejorar la calidad de la energía. El objetivo del control es que el inversor extraiga la potencia activa suministrada por la fuente de corriente continua y elimine el voltaje de secuencia negativa en la salida del inversor. En primer lugar, se analiza el mecanismo de generación de secuencias positiva y negativa bajo voltajes de red desbalanceados y se propone un esquema de separación de secuencias basado en el Integrador Generalizado de Segunda Orden (SOGI) para completar la separación de voltajes de secuencias positiva y negativa. Para eliminar el voltaje de secuencia negativa en la salida del convertidor, el convertidor inyecta una corriente de secuencia negativa. Se propone un generador de corriente de referencia basado en el voltaje de red virtual y se establece un modelo matemático de la microrred SEPIC real para calcular el valor de la inductancia virtual. Posteriormente, se obtienen los valores de referencia de la corriente mediante la separación de secuencias positiva y negativa con SOGI y el nuevo generador de corriente de referencia. Se utiliza un controlador PRES para mejorar el desbalance de voltaje en la microrred y lograr un seguimiento sin errores de las señales sinusoidales. Las simulaciones se realizaron en MATLAB/Simulink para validar la eficacia del método propuesto., In the context of the increasing integration of renewable energy sources into electrical grids, grid-connected inverters play a crucial role. However, one of the most significant challenges associated with these devices is the presence of unbalanced voltage components at the point of common coupling (PCC), especially the negative sequence voltage. This phenomenon can negatively affect power quality and system stability. This research focuses on the analysis and reduction of the negative sequence voltage at the output of grid-connected inverters to improve power quality. The control objective is for the inverter to extract the active power supplied by the direct current source and eliminate the negative sequence voltage at the inverter output. Firstly, the generation mechanism of positive and negative sequences under unbalanced grid voltages is analyzed, and a sequence separation scheme based on the SecondOrder Generalized Integrator (SOGI) is proposed to complete the separation of positive and negative sequence voltages. To eliminate the negative sequence voltage at the converter output, the converter injects a negative sequence current. A reference current generator based on the virtual grid voltage is proposed, and a mathematical model of the actual SEPIC microgrid is established to calculate the value of the virtual inductance. Subsequently, the reference current values are obtained through the separation of positive and negative sequences using SOGI and the new reference current generator. A Proportional Resonant (PRES) controller is used to improve the voltage unbalance in the microgrid and achieve error-free tracking of sinusoidal signals. Simulations were carried out in MATLAB/Simulink to validate the effectiveness of the proposed method.

2023/2024, 2n quadrimestre

A microgrid is a group of interconnected loads and distributed energy resources that can fill the gap between the dependence on a bulk power grid and the transition to renewable energies. The islanded mode presents itself as the most interesting scenario, when local controllers should maintain the power quality standards based on several parameters. A tool specifically focused on the process of parameter tuning of the secondary consensus-based control for inverter-based islanded microgrids was proposed in this paper. One often-quoted drawback in this process is the great number of parameters that must be tuned, even for a very simple microgrid structure. To manage such a large number of parameters, the design of experiments was used in this study. The main motivation for this work was to present an optimized way to define the correct parameters for the secondary consensus control for inverter-based islanded microgrids. The study shows how experimental design methodology can be an efficient tool to tune microgrid parameters, which are typically multi-objective-based experiments. From the results, it is correct to state that the design of experiments is able to reach the optimal setting with a minimal number of experiments, which would be almost impossible to obtain with the trial-and-error method., This work was supported by the Brazilian agencies of the Council for Scientific and Technological Development (CNPq), Coordination for the Improvement of Higher Education Personnel (CAPES), and Research Support Foundation of the Minas Gerais State (FAPEMIG). This publication is part of the R&D project PID2021-122835OB-C21, financed by MCIN/AEI/10.13039/ 501000011033 and FEDER “Una manera de hacer Europa”., Peer Reviewed, Postprint (published version)

Títol diferent a la intranet docent de l'EPSEVG: "Control de convertidores en microrredes aisladas durante cortocircuitos", Este documento propone nuevas estrategias de limitación de corriente para proteger a inversores trifásicos en modo “grid-feeding” ante sobrecorrientes causadas por fallos en la red eléctrica. A diferencia de estrategias ya existentes para estas situaciones, estos controles alternativos no requieren reducir, a priori, todas las corrientes del convertidor simultáneamente para limitar la corriente máxima del convertidor. Esto permite que se pueda dar prioridad a una consigna de funcionamiento del inversor específica por encima del resto al aplicar la estrategia correcta. Se estudian dos tipos de condiciones anormales de red distintas: tensión entre fases Vabc simétrica y asimétrica. Para cada una se propone un funcionamiento del inversor coherente acorde al fallo producido. El diseño de las estrategias alternativas se acompaña de un gran número de explicaciones sobre el fundamento teórico de las mismas. Además, se presentan los resultados experimentales obtenidos tras implementar cada una de las estrategias en un entorno práctico para corroborar la validez del estudio., This document presents new current limitation strategies to protect three-phase inverters in grid-feeding mode against overcurrent produced by grid faults. Unlike already existing strategies for these situations, these alternative control methods do not require, in most cases, to lower all converter’s currents simultaneously to limit the maximum current. This allows one to prioritize one of the inverter's operating references ahead of others by applying the correct strategy. Two different types of abnormal grid conditions are studied: symmetric and asymmetric phase-to-phase voltages Vabc. For each case, a coherent inverter operation is proposed. The design of alternative strategies is presented along with a large number of explanations regarding the theoretical base of each strategy. Moreover, experimental results obtained after implementing each strategy in a practical environment have been included to corroborate the validity of the study.

El objetivo de este proyecto es realizar el cálculo, diseño y simulación de un cargador bidireccional con aplicaciones vehículo a red para un vehículo eléctrico, principalmente para vehículos eléctricos particulares tipo Nissan Leaf, Nissan eNV200, Renault ZOE o Ford F-150 Lightning. Además de hacer el cálculo, diseño y simulación de un cargador bidireccional para aplicaciones vehículo a red, primero se hará una introducción de los diferentes conceptos para proporcionar ciertas nociones sobre que es la tecnología vehículo a red donde se explicarán las diferentes variables que tiene y sus aplicaciones, como funciona esta tecnología, las ventajas y desventajas que presenta y la normativa que tiene que cumplir esta tecnología. También se hará un estudio del arte para poder ver las diferentes topologías de electrónica de potencia aplicadas a esta tecnología, además se hará un pequeño estudio de mercado para ver los cargadores bidireccionales que hay actualmente en el mercado, sus características de funcionamiento y quien los fabrica. Una vez realizada la parte teórica se procederá al diseño, cálculo, modelado y simulación de una topología de electrónica de potencia aplicada a la tecnología vehículo a red. Primeramente se hará el diseño del circuito y el control de este, para después realizar los cálculos de los diferentes componentes que comprenden el circuito que se diseñara, una vez realizados los cálculos se modelara y simulara en diferentes entornos de funcionamiento, la herramienta con la que se modelara y simulara es SIMULINK la cual pertenece al grupo de aplicaciones de MATLAB., L'objectiu d'aquest projecte és fer el càlcul, el disseny i la simulació d'un carregador bidireccional amb aplicacions vehicle a xarxa per a un vehicle elèctric, principalment per a vehicles elèctrics particulars tipus Nissan Leaf, Nissan eNV200, Renault ZOE o Ford F-150 Lightning. A més de fer el càlcul, el disseny i la simulació d'un carregador bidireccional per a aplicacions vehicle a xarxa, primer es farà una introducció dels diferents conceptes per proporcionar certes nocions sobre què és la tecnologia vehicle a xarxa on s'explicaran les diferents variables que té i les seves aplicacions, com funciona aquesta tecnologia, els avantatges i els desavantatges que presenta i la normativa que ha de complir aquesta tecnologia. També es farà un estudi de l'art per poder veure les diferents topologies d'electrònica de potència aplicades a aquesta tecnologia, a més es farà un petit estudi de mercat per veure els carregadors bidireccionals que hi ha actualment al mercat, les seves característiques de funcionament i qui els fabrica. Un cop feta la part teòrica es procedirà al disseny, càlcul, modelatge i simulació d'una topologia d'electrònica de potència aplicada a la tecnologia vehicle a xarxa. Primerament es farà el disseny del circuit i el control d'aquest, per després realitzar els càlculs dels diferents components que comprenen el circuit que es dissenyés, un cop realitzats els càlculs es modelarà i simularà en diferents entorns de funcionament, l'eina amb què es modelarà i simularà és SIMULINK la qual pertany al grup d'aplicacions de MATLAB., The objective of this project is to carry out the calculation, design and simulation of a bidirectional charger with vehicle-to-grid applications for an electric vehicle, mainly for private electric vehicles such as Nissan Leaf, Nissan eNV200, Renault ZOE or Ford F-150 Lightning. In addition to calculating, designing, and simulating a bidirectional charger for vehicle-to-grid applications, first there will be an introduction to the different concepts to provide certain notions about what vehicle-to-grid technology is, where the different variables it has and its consequences will be explained. applications, how this technology works, the advantages and disadvantages it presents and the regulations that this technology must comply with. There will also be a study of the art to be able to see the different topologies of power electronics applied to this technology, in addition there will be a small market study to see the bidirectional chargers that are currently on the market, their operating characteristics and who makes them. Once the theoretical part has been completed, we will proceed to the design, calculation, modeling and simulation of a power electronics topology applied to vehicle-to-grid technology. Firstly, the design of the circuit and its control will be made, to later carry out the calculations of the different components that comprise the circuit to be designed, once the calculations have been made, it will be modeled and simulated in different operating environments, the tool with which It will be modeled and simulated is SIMULINK which belongs to the MATLAB group of applications.

Line-to-line short circuits are the transient disturbances that cause the highest currents as well as the largest voltage imbalances in inverter-based microgrids. This paper presents a control scheme for grid-forming inverters in islanded microgrids that limits the current to a safe value during these types of short circuits while providing a lower voltage imbalance compared to state-of-the-art current limiting techniques. This control scheme is based on reducing both the amplitude of the reference voltage with the maximum amplitude of the reference current and the instantaneous reference voltage with only the inductive component of the virtual impedance. The combination of these two control actions provides low voltage imbalance, as the theoretical and experimental studies reveal. This voltage imbalance improvement is the main contribution of this paper and is maintained when the microgrid supplies linear and non-linear loads. In the theoretical study, the paper includes control design guidelines to satisfy static and dynamic specifications. The theoretical predictions are validated by means of experimental results measured in a laboratory microgrid. A practical performance comparison of current limiting techniques based on experimental tests is also reported., This publication is part of the project PID2021-122835OB-C21, financed by MCIN/AEI/10.13039/501000011033 and FEDER “Una manera de hacer Europa”., Postprint (published version)

In islanded microgrids, when a short circuit or a sudden overload occurs, it provokes an abrupt increment in the currents supplied by the generation nodes, which feed the load collaboratively. This is particularly challenging for inverter-based nodes, due to its reduced power capacity. This work takes advantage of the droop-method basic configuration to propose an additional closed-loop control, which ensures maximum current injection during any kind of short circuit maintaining the underlying droop control. Ensuring that any node injects its maximum rated current during the short circuit, it emulates the most common low-voltage ride-through protocols for grid-feeding sources oriented to support the grid and, in this way, the voltage unbalance is reduced. To develop the control proposal, a model of the faulted system is presented in order to evaluate the stability of the closed-loop system. A general modelling methodology is introduced in order to derive the control for any microgrid configuration. Finally, selected experimental results are reported in order to validate the effectiveness of the proposed control., Peer Reviewed, Postprint (author's final draft)

This paper presents a model predictive control (MPC) for a grid-connected voltage source inverter (VSI) with current limitation. The control algorithm is performed in the dq frame to obtain the amplitude of the inverter currents. First, a state observer with a reduced model of the converter is used to estimate the inverter current and perform active damping. Then, an MPC algorithm is used to regulate the currents to a desired reference but with the advantage that these currents can be limited to a maximum value by introducing a constraint in the cost function instead of clipping the current of the inverter above a maximum current. This controller has been tested experimentally under a current reference step change and without a physical damping resistor., This publication is part of the project I+D+i PID2021-122835OB-C21, financed by MCIN/AEI/10.13039/501000011033 and FEDER “Una manera de hacer Europa”., Peer Reviewed, Postprint (author's final draft)

© 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., The number of electric vehicles connected to the grid is growing constantly due to environmental and regulatory issues. Using these connected vehicles as distributed generators is a promising future functionality, known as vehicle to grid concept. When connected to an islanded microgrid, the electric vehicles can collaborate to support the overall system stability. Specially during grid faults, as voltage sags or over currents, when electric vehicles can mimic the low voltage ride through protocols required to distributed generators. This work deals with an islanded microgrid with electric vehicles injecting reactive power when a sag occurs. The control proposal has three main objectives: from the microgrid point of view, it provides optimized voltage support reducing the voltage unbalance and avoids over voltages in the less faulty phases; from electric vehicle point of view, it avoids active power oscillations which affects positively to the lifespan of the electric vehicle charger-components. Selected experimental results demonstrate the effectiveness of the control proposal., This publication is part of the project I + D + I RTI2018–100732 – B – C22, financed by MCIN / AEI / 10.13039 / 501000011033 and FEDER “Una manera de hacer Europa"., Peer Reviewed, Postprint (author's final draft)

The use of renewable energies and their participation in the electricity market has been increasing in recent years with the aim of achieving a future where 100% of the generation comes from renewable sources. In this new scenario, in which most of the synchronous generators with high inertias will no longer participate, the main reference of the network will have to be formed in an alternative and robust way. Given that renewable energy generation and storage systems require power converters to adapt to an AC grid, they already now shall have power distribution control algorithms based on the network voltage and frequency. On the other hand, a power converter can behave and be modeled as a controlled voltage source or controlled current source according to the variable that is been regulated. In the absence of synchronous generators in the future, the formation and responsibility of a stable grid must be distributed among different converters working as voltage controlled sources with power distribution algorithms. When a converter works as a controlled voltage source, it presents a new challenge in the field of the corresponding control algorithm when facing a fault scenario at the grid side. In the event of a short circuit, the output current of the inverter must be saturated to prevent possible damage of the inverter. This limitation can have consequences for the upper control loops if they are not consistently adapted. This master thesis presents a new control strategy for dealing with short-circuit scenarios by saturating the amplitude of the reference voltage from the droop power distribution loop. In this way, possible windup effects are avoided, which would cause the instability of the system., El uso de las energias renovables y su participación en el mercado eléctrico viene en aumento durante los últimos años con el objetivo de alcanzar un futuro donde el 100% de la generación provenga de fuentes renovables. En este nuevo escenario, en el cual los generadores síncronos con grandes inercias dejarán de participar en gran medida, la red principal de referencia deberá formarse de una manera alternativa y rebusta. Teniendo en cuenta que los sistemas de generación renovables y almacenamiento de enegia eléctrica requieren de convertidores de potencia para adaptarse a una red AC, estos en la actualidad ya deben contar con algoritmos de control de distribución de potencia en función de la tensión y frecuencia de la red. Por otro lado, un convertidor de potencia puede comportarse y modelarse como una fuente de tensión controlada o fuente de corriente controlada según la variable a monitorizar. En un futuro ausente de generadores síncronos, la formación y responsabilidad de una red estable debe estar distribuida entre los distintos convertidores trabajando como fuente de tensión controlada con algoritmos de distribución de potencia. Cuando un convertidor trabaja como fuente de tensión controlada presenta un nuevo reto en el ámbito del correspondiente algoritmo de control frente a un escenario de falta en el lado de la red. En caso de cortocircuito, la corriente de salida del convertidor debe saturarse para evitar posibles daños de este. Esta limitación, puede tener consecuencias en los lazos de control superiores si estos no son adaptados de forma coherente. Este trabajo presenta una nueva estrategia de control para abordar escenarios de cortocircito mediante la saturación de la amplitud de la tensión de referencia proviniente del lazo de repartición de potencias "droop". De esta forma, se evitan posibles efectos de "windup", los cuales causarian la inestabilidad del sistema., L'ús de les energies renovables i la seva participació en el mercat elèctric ve en augment durant els darrers anys amb l'objectiu d'assolir un futur on el 100% de la generació provingui de fonts renovables. En aquest nou escenari, en el qual els generadors síncrons amb grans inèrcies deixaran de participar-hi en gran mesura, la xarxa principal de referència haurà de formar-se d'una manera alternativa i robusta. Tenint en compte que els sistemes de generació renovables i emmagatzemament d'energia elèctrica requereixen de convertidors de potència per a adaptar-se a una xarxa AC, aquests en la actualitat ja han de comptar amb algoritmes de control de distribució de potència en funció de la tensió i freqüència de la xarxa. Per altra banda, un convertidor de potència pot comportarse i modelarse segons una font de tensió controlada o font de corrent controlada segons la variable a monitoritzar. En un futur absent de generadors síncrons, la formació i responsabilitat d'una xarxa estable ha d'estar distribuida entre diferents convertidors treballant com a font de tensió controlada amb algoritmes de distribució de potència. Quan un convertidor treballa com a font de tensió controlada presenta un nou repte en l'àmbit del corresponent algoritme de control davant un escenari de falta al costat de la xarxa. En cas de curtcircuit, la corrent de sortida del convertidor s'ha de saturar per a evitar possibles danys d'aquest. Aquesta limitació, pot tenir conseqüènices ens els llaços de control superiors si aquests no són adaptats coherentment. Aquest treball presenta una nova estrategia de control per a afrontar escenaris de curtcircuit mitjançant la saturació de l'amplitud de la tensió de referència provinent del llaç de repartició de potència "droop". D'aquesta forma, s'eviten possibles efectes de "windup", els quals causarien la inestabilitat del sistema.

© 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., The number of electric vehicles connected to the grid is growing constantly due to environmental and regulatory issues. Conventionally these vehicles work as variable loads, although using them as distributed generators is a promising future functionality, known as vehicle to grid concept. Using vehicle to grid capacities to support the grid during voltage sags, emulating Low Voltage Ride Through protocols, have been studied extensively, also in the field of islanded microgrids based on power electronics converters. This work proposes a change of paradigm for low voltage islanded microgrids, where the network impedances are mainly resistive. Instead of injecting reactive currents during the sag, this work proposes the injection of unbalanced active currents with two main objectives. First, support the microgrid voltage prioritizing in the reduction of voltage unbalance to avoid over voltages in the less faulty phases. And second, collaborate in the active power injection with the distributed generators to supply the over currents that demands the system during short circuits which produce voltage sags. Selected simulation results demonstrate the effectiveness of the control proposal., This publication is part of the project I + D + I RTI2018–100732 – B – C22, financed by MCIN / AEI / 10.13039 / 501000011033 and FEDER “Una manera de hacer Europa"., Peer Reviewed, Postprint (author's final draft)

The objective of this project is to analyze the impact that solar panels and electric vehicles would have on the power grid, specifically, the injection and/or absorption of reactive power by the inverters of these. Prior to the topic in question, the document contains a brief explanation of the climate situation, energy and smart grids (all of which are core topics in the document). The study will be carried out with simulations made by Simulink on 3 different cases. The first and second case will consist of single-phase inverters, while the third case will be run with three-phase inverters. Each case will vary the number of houses that will be connected to the grid. Apart from the incidence of reactive power, in case 3, the behavior of the system subjected to disturbances in the electrical grid will also be studied. The work consists of all the necessary explanations to fully understand the operation of the Matlab and Simulink simulation files. The Excel program will also be used for some graphics., El objetivo de este proyecto es analizar el impacto que tendrían los paneles solares y los vehículos eléctricos en la red eléctrica, concretamente, la inyección y/o absorción de potencia reactiva por parte de los inversores de éstos. Previo al tema en cuestión, el documento contiene una breve explicación de la situación climática, la energía y las redes inteligentes (todos ellos temas centrales en el documento). El estudio se llevará a cabo con simulaciones realizadas mediante Simulink sobre 3 casos diferentes. El primer y el segundo caso consistirán en inversores monofásicos, mientras que el tercer caso se ejecutará con inversores trifásicos. En cada caso se variará el número de viviendas que se conectarán a la red. Además de la incidencia de la potencia reactiva, en el caso 3 se estudiará también el comportamiento del sistema sometido a perturbaciones en la red. El trabajo consta de todas las explicaciones necesarias para comprender el funcionamiento de los archivos de simulación Matlab y Simulink. También se utilizará el programa Excel para algunos gráficos., L'objectiu d'aquest projecte és analitzar l'impacte que tindrien els panells solars i els vehicles elèctrics a la xarxa elèctrica, concretament la injecció i/o absorció de potència reactiva per part dels inversors. Previ al tema en qüestió, el document conté una breu explicació de la situació climàtica, l'energia i les xarxes intel·ligents (tots ells temes centrals al document). L’estudi es durà a terme amb simulacions realitzades mitjançant Simulink sobre 3 casos diferents. El primer i segon cas consistiran en inversors monofàsics, mentre que el tercer cas s'executarà amb inversors trifàsics. En cada cas es variarà el nombre d’habitatges que es connectaran a la xarxa. A més de la incidència de la potència reactiva, en el cas 3 també s'estudiarà el comportament del sistema sotmès a pertorbacions de la xarxa. El treball consta de totes les explicacions necessàries per comprendre el funcionament dels fitxers de simulació empreats de Matlab i Simulink. També es farà servir el programa Excel per a alguns gràfics.

In 2015 the United Nations established the 17 Sustainable Development Goals: a set of interrelated objectives and a guide to reach a more sustainable and higher quality future for all humanity. The goals were set with a timeline for 2030, the seventh goal refers specifically to the universal access to “affordable and clean energy”. Taking account the considerable fraction of world population that do not have access to electricity, especially in rural areas, this goal still requires a great effort and investment. Rural hybrid microgrids, that integrate and manage solar and wind energy resources to provide electric service to remote locations, are a promising solution to reach this “last mile” scenario. However, as is reported in the literature, there is still scarce information about the performance of these systems based on measured data obtained in real working field conditions. This work aims to contribute to this aspect mainly by analyzing the data obtained in the 9 kW Laguna Grande community hybrid microgrid, which is cooperative since 2016 in the coast of Perú, and has been equipped with sensors and data acquisition systems that measure and register solar radiation, wind speed, temperatures, and all the relevant electric parameters. As a preliminary study, the rural electrification gap and costs are assessed, as well as the availability of solar and wind resources in the area of interest. A literature and state of the art review is undertaken followed by the definition of the microgrid concept and the different ways in which a rural microgrid can be configured. The particular way in which the Laguna Grande microgrid is configured and instrumented is described. Measured meteorological conditions as solar radiation, wind speed and temperature are analyzed and related to the power generated by the photovoltaic arrays and wind turbine. This in turn leads to a balance with respect to the power delivered to the community and consequently to the voltage levels of the, En el año 2015 las Naciones Unidas estableció los 17 Objetivos de Desarrollo Sostenible: un conjunto de objetivos interrelacionados y una guía para alcanzar un futuro más sostenible y de mayor calidad para toda la humanidad. Las metas se establecieron con una línea de tiempo para el 2030, la séptima meta se refiere específicamente al acceso universal a “energía limpia y asequible”. Teniendo en cuenta la fracción considerable de la población mundial que no tiene acceso a la electricidad, especialmente en las zonas rurales, este objetivo aún requiere un gran esfuerzo e inversión. Las microrredes híbridas rurales, que integran y gestionan los recursos de energía solar y eólica para proporcionar servicio eléctrico a lugares remotos, son una solución prometedora para llegar a este escenario de “última milla”. Sin embargo, como se reporta en la literatura, aún existe poca información sobre el desempeño de estos sistemas basada en datos medidos y obtenidos en condiciones operativas, reales de campo. Este trabajo busca contribuir en este aspecto principalmente mediante el análisis de los datos obtenidos en la microrred híbrida comunitaria de 9 kW en Laguna Grande, que está operativa desde 2016 en la costa de Perú. Esta microrred ha sido equipada con sensores y sistemas de adquisición de datos que miden y registran la energía solar, radiación, velocidad del viento, temperaturas y todos los parámetros eléctricos relevantes. Como estudio preliminar se evalúa la brecha y costos de electrificación rural, así como la disponibilidad de recurso solar y eólico en la zona de interés. Se realiza una revisión bibliográfica y del estado del arte, seguida de la definición del concepto de microrred y las diferentes formas en que se puede configurar una microrred rural. Se describe la forma particular en que se configura e instrumenta la microrred de Laguna Grande. Las condiciones meteorológicas medidas como la radiación solar, la velocidad del viento y la temperatura se analizan y relacio, Postprint (published version)

Resolved, 2021/2022, 2n quadrimestre

Resolved, 2021/2022, 2n quadrimestre

The primary and secondary distribution grids are typically designed separately and operated with a radial configuration; therefore, specialized load flow methods only applicable to radial or weakly meshed networks are normally used. However, projections indicate that the distribution grids will be more interconnected in the future, mainly because of the inclusion of distributed generation, voltage and reliability optimization, as well as an efficiency improvement when the primary and secondary networks are considered in an integrated way. For this new meshed grids scenario, the efficient and precise typically used load flow methods for distribution networks are no longer applicable and it becomes necessary using load flow algorithms that are also applicable for meshed configurations, such as the ones classically used for transmission networks like the Newton-Raphson, Gauss-Seidel and Gauss Implicit Z-bus methods, while also procuring to avoid potential singularity problems which may arise when dealing with long radial grids. In this work, variations of the Gauss-Seidel and Gauss Implicit Z-bus methods are presented, that are adequate for low and medium voltage grids regardless of the network configuration. Additionally, a linear, direct, and non-iterative load flow variation is presented as well as a comparison between different possible convergence criteria for the classical methods., Peer Reviewed, Postprint (author's final draft)

This paper presents a real-time control strategy for electric-vehicle based microgrids to mitigate voltage sags in large parking lots. It is programmed into the digital processors of the battery chargers and consists on the injection of reactive current by both positive- and negative sequence components. As main characteristics, it should be noted that the control strategy can function correctly during both balanced and unbalanced voltage sags and is an economical solution since it does not require the inclusion of additional power converters to improve power quality. This study also looks at the ability to mitigate voltage sags based on the number of parked vehicles., This work is part of the project I+D+i RTI2018-100732-B-C22, funded by MCIN/AEI/10.13039/501000011033 and FEDER “Una manera de hacer Europa (A way to make Europe)"., Peer Reviewed, Postprint (author's final draft)

© 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., Small-signal models are the mostly used to model and design in inverter-dominated microgrids. Conversely, this paper proposes a large-signal model for grid-forming inverters connected to a microgrid based on the active and reactive power dynamic equations. In this work, it is proposed to use this nonlinear model to develop a constrained predictive control for the inverters connected to a microgrid. The main features of this proposed control are: first, direct voltage control (in amplitude and frequency) is not necessary; second, stability is guaranteed under a wide range of line impedances (hence, the virtual impedance is not needed); and third, the proposed control can operate with unbalanced and nonlinear loads. Moreover, a theoretical stability analysis is presented. Selected experimental results show that the proposed control operates satisfactorily in case of a load step change, a load imbalance, and nonlinear loads., Peer Reviewed, Postprint (author's final draft)

© 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, The presence of unbalanced loads in power systems creates voltage imbalances that perturb the operation of sensitive loads like induction motors, power electronics converters and adjustable speed drives. This paper presents a novel control scheme that achieves accurate voltage balance at any node of an islanded AC microgrid with seamless integration with the existing hierarchical control of the microgrid. A master-slave architecture is adopted for the unbalance compensation due to its low network traffic requirements and its modular conception. The unbalance compensation follows a collaborative principle where current injections are computed as a function of the current rating of each inverter thus avoiding the overcurrent stress of the unbalance compensation by a single inverter. The paper presents the stability analysis and the design guidelines for the control parameters. The performance of the control proposal has been successfully tested in a laboratory microgrid. Selected experimental results are presented., Postprint (author's final draft)

Desde hace tiempo, la red trifásica eléctrica y otras composiciones trifásicas, sufren de diferentes fallos eléctricos los cuales deben ser controlados. En el caso de este TFM, el fruto de estudio es la falla eléctrica denominada cortocircuito. Estos cortocircuitos dan una problemática la cual se estudia en este proyecto. Uno de los más importantes es el incremento considerable de las corrientes, provocando así sobrecorrientes, en el momento en el que se produce del cortocircuito. Por eso, este TFM se basa en el estudio y entendimiento de los cortocircuitos y en como mitigar, mediante técnicas de control de limitación de corriente, el efecto de estos mismos. Para ello se ha construido una mr aislada la cual se compone a partir de seis inversores de potencia, seis transformadores y una serie de inductancias para modelizar el conexionado entre los inversores. En este sistema, durante un tiempo determinado, se fuerza la interconexión entre dos fases, para provocar así un cortocircuito entre fases. Posteriormente al fuerce del cortocircuito, y tras haber estudiado las tres diferentes técnicas de limitación de corriente que se aplican, estas son implementadas, junto a toda la mr, mediante el programa Matlab/Simulink. Con ello, se deducirán cuáles son los beneficios de cada una de las técnicas de control y se detallaran cuáles son los resultados de todas las técnicas utilizadas, para que puedan ser así comparadas. Para finalizar el proyecto, se realizara la pertinente conclusión, para de forma objetiva y basándose en los datos y resultados obtenidos, concluir en cuál es la técnica que presenta mayor beneficios en términos de mitigar los efectos del cortocircuito entre fases., For a long time, the three-phase electrical network and other three-phase compositions have been suffering from different electrical faults which must be controlled. In the case of this TFM, the object of study is the electrical fault called short-circuit. These short circuits give a problem which is studied in this project. One of the most important is the considerable increase in currents, thus causing overcurrents, at the moment when the short-circuit occurs. Therefore, this TFM is based on the study and understanding of short circuits and how to mitigate, by means of current limiting control techniques, the effect of these short circuits. For this purpose, an isolated microgrid has been built, which is composed of six power inverters, six transformers and a series of inductances to model the connections between the inverters. In this system, for a given time, the interconnection between two phases is forced, thus causing a short-circuit between phases. After forcing the shortcircuit, and after having studied the three different current limiting techniques that are used, these are implemented, together with the entire microgrid, using the Matlab/Simulink program. In this way, the benefits of each of the control techniques will be deduced and the results of all the techniques used will be detailed so that they can be compared. To close the project, the relevant conclusion will be drawn, in order to objectively and based on the data and results obtained, conclude which technique is the most beneficial in terms of mitigating the effects of shortcircuit between phases.

© 2021 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., This paper presents a control scheme that simultaneously solves the problems of negative-sequence voltage compensation and negative-sequence current sharing in grid-connected microgrids using grid-feeding inverters. State-of-the-art schemes have previously solved these problems with low-performance control solutions or, alternatively, with high-performance solutions but paying the cost of high control-data traffic in the communication network. The proposed control scheme improves the performance of previous schemes for grid-feeding inverters with the following characteristics: 1) negative-sequence voltage compensation at any point of the microgrid, 2) accurate negativesequence current sharing, and 3) low control-data traffic. In terms of implementation, two key points of the proposed control scheme are: the voltage compensation is based on a band-pass filter with complex coefficients and the current sharing is reached only with local current measurements. In the theoretical analysis, the system model is based on transfer functions with complex coefficients. This fact facilitates the control design due to 1) the system model is linear in this complex domain and 2) the multiple-input singleoutput model can be represented as a single-input single-output model for voltage compensation. The characteristics of the proposed control are validated by means of experimental results measured in a laboratory microgrid., This work is part of the project I+D+I RTI2018-1000732-B-C22, funded by MCIN/AEI/10.13039/501000011033 and FEDER “A way to make Europe”., Peer Reviewed, Postprint (author's final draft)

This paper seeks to quantify the effects of the increasing penetration level of renewable distributed generation and energy storage systems on the regulated electricity market over time. More specifically, the emphasis is on the long-term implications of distributed energy resources on energy loss and how it affects the electricity market. The proposed methodology is based on a modified combination of the Bass diffusion model (time-series forecasting of the penetration level of distributed energy resources) and the optimized tariff model (socioeconomic regulated electricity market model). Such models have not previously been applied jointly, even though they exhibit great potential for long-term market assessment in the context of distributed energy resources integration. The methodology enables the analysis of multiple public policies regarding renewable distributed generation and energy storage systems, such as net billing schemes to accelerate their deployment. Furthermore, the methodology also enables the assessment of energy storage systems’ feasibility. By applying the methodology to a concession area in southern Brazil, results demonstrate that energy storage systems are feasible if combined with appropriate public policies, as a performance index (mean socioeconomic gain) of 329 (MR$) was obtained., The authors wholeheartedly recognize the seminal contributions of Prof. Hector Arango (In Memoriam) in creating the former optimized tariff model (absence of DG and ESS) and in proofreading this paper. The authors gratefully acknowledge the support of the Federal University of Itajuba and Universitat Politècnica de Catalunya. The authors also gratefully acknowledge the financial support in part of CAPES – Coor-denaç˜ao de Aperfeiçoamento de Pessoal de Nível Superior – Brazil – Finance Code 001, CNPq – National Council for Scientific and Techno-logical Development – Brazil, INERGE, and FAPEMIG. Finally, the au-thors value the support of Jéssica Polite in increasing the figures’ resolution., Peer Reviewed, Postprint (author's final draft)

La necesidad de mejorar la calidad de las redes eléctricas, cumpliendo con los aspectos económicos, sociales y ambientales, representa un importante desafío, que trata de ser resuelto con la integración de fuentes de energía renovables y generación distribuida. Gracias a la exitosa integración de la electrónica de potencia y las tecnologías de nueva generación, la generación distribuida se ha vuelto cada vez más competitiva frente a un sistema centralizado convencional y atrae a muchos clientes de los sectores industrial, comercial y residencial. Una de las soluciones planteadas son las microrredes, que utilizan sistemas de distribución de baja tensión con recursos energéticos distribuidos (DER) como microturbinas, pilas de combustible, paneles fotovoltaicos...junto con dispositivos de almacenamiento, ofreciendo considerables capacidades de control sobre el funcionamiento de la red. Estos sistemas suelen estar interconectados a la red de distribución de media tensión, pero también se pueden operar aislados de la red principal en caso de fallos en la red. Los fallos en la red producen uno de los fenómenos más típicos en los sistemas de potencia, el desequilibrio de voltaje. La presencia de voltajes desequilibrados puede resultar en impactos adversos en el equipo y el sistema de energía. En este proyecto se presentan dos métodos de control para la eliminación de los desequilibrios de tensión, que intentan eliminar la tensión de secuencia negativa, uno basado en la eliminación de la tensión de secuencia negativa en la salida del inversor y el otro basado en una tensión virtual. La mayoría de las propuestas de control existentes sirven para varios objetivos de control, que pueden ser mitigación de desequilibrio, desplazamiento de voltaje, mitigación de fluctuación de voltaje, eliminación de armónicos...considerando diferentes tipos de impedancias de red. Sin embargo, ninguno de ellos consigue eliminar la tensión de secuencia negativa que genera el desequilibrio de red s, The need to improve the quality of the electrical grids, fulfilling economic, social and environmental aspects, represents a challenging issue, which tries to be solved with the integration of energy sources and distributed generation. Thanks to the successful integration of power electronics and new generation technologies, distributed generation has become increasingly competitive against the conventional centralized system and attracting many customers from the industrial, commercial and residential sectors. One of the solutions is microgrids, which comprise low voltage distribution systems with distributed energy resources (DERs) such as microturbines, fuel cells, photovoltaic (PV) arrays...together with storage devices, offering considerable control capabilities over the grid operation. These systems are interconnected to the medium voltage distribution grid, but they can be also operated isolated from the main grid in case of faults in the upstream grid. Grid faults produce one of the most typical phenomena in power systems, the voltage unbalance. The presence of unbalanced voltages may result in adverse impacts on equipment and power system. In this project, two control methods are presented for the elimination of voltage unbalances, which try to eliminate the negative sequence voltage, one based on the elimination of the negative sequence voltage at the inverter output and the other, based on a virtual voltage. Most of the existing control proposals serve various control objectives, which can be unbalance mitigation, voltage deviation, voltage fluctuation mitigation, harmonic elimination...considering different types of grid impedances. However, none of them succeeds in eliminating the negative sequence voltage that generates the imbalance of the grid without depending on the specific impedance of the grid. Focused on the grid-feeding converters, this work presents a control strategy that aims to eliminate negative sequence voltage, which is robust to variat

Hybrid microgrids constitute a promising solution for filling the electricity access gap that currently exists in rural areas; however, there is still relatively little information about their reliability and costs based on measured data in real working conditions. This article analyzes data obtained from the operation of a 9 kW hybrid microgrid in the fishermen’s cove of Laguna Grande, Paracas, in the Ica region of Perú, which has been running for 5 years. This microgrid has been equipped with data acquisition systems that measure and register wind speed, solar radiation, temperatures, and all the relevant electric parameters. Battery dynamics considerations are used to determine the depth of discharge in a real-time operative situation. The collected data are used to optimize the design using the specialized software HOMER, incorporating state-of-the-art technology and costs as a possible system upgrade. This work aims to contribute to better understanding the behavior of hybrid rural microgrids using data collected under field conditions, analyzing their reliability, costs, and corresponding sensitivity to battery size as well as solar and wind installed power, as a complement to a majority of studies based on simulations., Peer Reviewed, Postprint (published version)

In this paper, a novel cascade model predictive control for a three-phase unity power factor rectifier is presented. Unlike the traditional control techniques for rectifiers, the proposed method uses a cascade dual-model predictive control for the inner and outer control loops. The three-phase currents of the rectifier are controlled with the inner control loop, while with the outer control loop the desired output voltage is achieved. In this proposal, the output power is used as a feedforward to enhance the transient dynamics of the output dc-voltage. Several advantages can be highlighted such as a fixed switching frequency and output-voltage variations are avoided when a sudden change in the load or a voltage sag appears. The overall control proposal has been fully integrated into a digital signal processor. Selected experimental results are introduced to validate the theoretical contributions of this paper., Peer Reviewed, Postprint (author's final draft)

Resolved

This paper presents a control scheme in the stationary reference frame for Static Synchronous Compensators that provides three features: 1) regulation of the positive sequence voltage to the nominal value, 2) full cancellation of the negative sequence voltage, and 3) peak limitation of the injected currents. These features can help improving the performance of these devices under perturbed grid conditions, including low, high and unbalanced voltages. Also, the peak current limiter guarantees both the safe operation of the converter, and a priority-based achievement of the voltage regulation targets, which is of interest during severe perturbations like voltage dips. Experimental results, implementation details and closed-loop analysis are presented to validate the regulation capabilities and to demonstrate the feasibility of the power quality improvement., This work was supported in part by the Ministry of Science, Innovation, and Universities of Spain and in part by the European Regional Development Fund under Project RTI2018-100732-B-C22., Peer Reviewed, Postprint (author's final draft)

© 2021 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, The control flexibility of the power inverters that interface distributed generation can be exploited to incorporate power quality enhancement features in addition to the usual power management control. This article presents a novel control scheme that achieves voltage balance at any node of an ac microgrid regardless of the impedance value of the power network. The collaborative strategy is devoted to set a specific sharing of the balancing currents, thus avoiding the adverse effects of the unbalance compensation by a single inverter. The control scheme uses a complex form of a proportional resonant controller and a communication link. The article presents the stability and sensitivity analysis and the design guidelines for the control parameters. The performance of the control proposal has been tested successfully in a laboratory microgrid setup. Selected experimental results are presented., Peer Reviewed, Postprint (author's final draft)

An inverter-based microgrid is a small-scale power network governed by a distributed con-trol system. In this system, the nodes are the digital controllers of the power inverters,normally located at separate points within the microgrid. A relevant issue is that thesecontrollers operate at different frequencies due to inherent clock deviations in the localhardware oscillators. This paper evaluates the effects of these c lock deviations on the per-formance of microgrids equipped with inverters that emulate the operation of synchronousmachines. A systematic procedure is presented to derive steady-state expressions of theinverter active power and microgrid frequency as a function of clock drift rates. This pro-cedure is applied to swing and governor equations of the virtual synchronous generators,revealing the mechanism that allows clock drifts to be absorbed, making their presencenegligible. In addition, it allows recognising the controllers that should never be imple-mented in a distributed control system, since they cause an unsatisfactory behaviour thatcan even lead to a blackout in the microgrid. Therefore, the relevance of this study is theidenti¿cation of the control schemes that are most sensitive to clock drifts, which makesit easier to choose the most suitable control implementation for a particular application.Furthermore, technical guidelines are reported to help researchers on developing controlsolutions more robust to clock drifts. In this study, the theoretical results are validated byexperimental tests in a laboratory microgrid., This work was supported by the Ministry of Science, Innova-tion and Universities of Spain and by the European RegionalDevelopment Fund under project RTI2018-100732-B-C22., Peer Reviewed, Postprint (published version)

The current Royal Decree 413/2014 legal-economic framework for concentrating solar power plants in Spain has been analysed from a probabilistic perspective. Due to the high inherent risk in most of the parameters defining this economic regime, the use of a probabilistic model is proposed to perform the economic valuation of these facilities. A methodology composed of different steps has been developed and applied to a representative concentrating solar power plant type with thermal energy storage. This method has proven useful for distinguishing the input parameters to be considered as stochastic by using a sensitivity analysis, and also for performing the probabilistic valuation by using the discounted cash flow-Monte Carlo analysis. The results have revealed a great variability in the several output economic indicators considered. In general terms, substantial reductions in the profitability of these facilities have been evidenced with respect to the deterministic analysis under the current reality of the sector., Peer Reviewed, Postprint (author's final draft)

Resolved

Inverters-based islanded microgrids are operated by local digital signal processors, driven by their own local clocks. These local clocks have drifts affecting the clock signals which are used to control the inverters in real time. In this scenario, a steady-state deviation is observed in active power sharing, degrading the microgrid performance. This paper presents a new control scheme that improves the microgrid performance by cancelling the active power sharing error due to clock drifts. The study includes a theoretical stability analysis and a design procedure of the control parameters based on the dynamic characteristics. Finally, selected experimental results are obtained in a laboratory microgrid with four inverters. In this setup, each inverter was equipped with its digital signal processor with drifting local clock., Postprint (published version)

Resolved

Resolved

© 2020 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., A major concern of the power quality in distributed systems is related to the mitigation of voltage imbalances. This function can be implemented directly in the control system of the distributed generation power converters working simultaneously with the standard operation modes. This study presents a negative-sequence voltage elimination technique for distributed generators in grid-feeding operation mode. The proposal guarantees a complete elimination of the negativesequence voltage, while operating without a priori in-depth knowledge of the grid configuration and its characteristics. The proposed control architecture is presented together with its pseudocode, a controller flowchart and a discussion of the implementation aspects. A closed-loop modelling is derived based on a complex transfer function approach, which is used to determine stability margins and control design guidelines. A laboratory setup was implemented to verify the performance of the proposed strategy., This work was supported by the Ministry of Science, Innovation and Universities of Spain and by the European Regional Development Fund under project RTI2018-100732-B-C22., Peer Reviewed, Postprint (author's final draft)

Resolved

Hierarchical schemes are widely used for the design of inverter-based AC microgrids control strategies. To ensure a reliable operation, hierarchical control must consider together all the functionalities that allow the regulation of key variables and guarantee a safe transition between operation modes. Conventionally, in the literature are proposed three-layer schemes which present relevant drawbacks: they include limited functionalities and they use droop method for the primary layer which, despite its decentralized nature, suffers from issues that have motivated the development of alternative strategies. Considering this, the contribution of this paper is twofold. First, a droop-free hierarchical control strategy that satisfy a proper operation of AC microgrids is proposed. Control objectives such as power-sharing, frequency regulation, optimal power dispatch, and voltage regulation are considered. Second, a closed-loop small-signal model, which facilitates the control parameters design and fills a gap in the literature is presented. Differences between the proposal and previous controls are discussed. Selected tests are carried out in a laboratory microgrid under different conditions, including normal operation and the response to failures in the central controller and to communication impairments. The experimental results show a good performance of the proposal even in adverse conditions., Peer Reviewed, Postprint (author's final draft)

Resolved

This paper is a postprint of a paper submitted to and accepted for publication in IET Power Electronics and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at the IET Digital Library., During voltage sags, distributed generation systems must fulfil specific grid-code requirements for reactive current injection. This ancillary service can produce overvoltage problems in networks operating in unbalanced conditions when the amplitude of one of the phase voltages is higher than the others and a balanced reactive current is injected through large grid impedance. This study proposes a control scheme to avoid these overvoltage problems, thus reducing the risk of cascade disconnection that this incident may produce. The derivation of the control scheme starts from the flexible oscillating-power control, introduces the necessary modifications so that this control meets the grid-code requirements for current injection and combines it with a slope voltage control to achieve a good voltage regulation. A theoretical analysis is included to determine the expressions that quantify the voltage support characteristics of the proposal. Finally, selected experimental results are reported to validate the characteristics of the proposed control., Peer Reviewed, Postprint (author's final draft)