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©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., The high penetration of distributed energy sources is changing the paradigm of electrical networks control and management. Nowadays, power conversion systems associated to green energy plants are not only required to deliver power according to an MPPT algorithm, but should also participate in the regulation and operation of the power system, in the case of large scale systems, or provide advanced features to end users in the case of prosumers. This work proposes the use of an active transformer, incorporating series voltage regulation and current shunt regulation, through two converters in back-to-back configuration, which is able to provide all power quality services as well as resilience to end-users. This topology is advantageous in case of prosumers connected to weak and faulty grids. Moreover, the proposed active transformer also includes a battery so that island operation is offered as a service. Throughout the paper, the stability analyses and the implementation of an active transformer are presented, with special emphasis on the control of the series converter. The proposed topology is validated through real time simulations and an experimental prototype which includes a 300 kWh energy storage installation., This work was supported in part by LC-SC3-ES5-2018-2020-INTERRFACE Project under Grant GA 824330 and FlexiGRID Project under grant RTI2018-100921-B-C21., Peer Reviewed, Postprint (author's final draft)

Smart energy networks provide an effective means to accommodate high penetrations of variable renewable energy sources like solar and wind, which are key for the deep decarbonisation of energy production. However, given the variability of the renewables as well as the energy demand, it is imperative to develop effective control and energy storage schemes to manage the variable energy generation and achieve desired system economics and environmental goals. In this paper, we introduce a hybrid energy storage system composed of battery and hydrogen energy storage to handle the uncertainties related to electricity prices, renewable energy production, and consumption. We aim to improve renewable energy utilisation and minimise energy costs and carbon emissions while ensuring energy reliability and stability within the network. To achieve this, we propose a multi-agent deep deterministic policy gradient approach, which is a deep reinforcement learning-based control strategy to optimise the scheduling of the hybrid energy storage system and energy demand in real time. The proposed approach is model-free and does not require explicit knowledge and rigorous mathematical models of the smart energy network environment. Simulation results based on real-world data show that (i) integration and optimised operation of the hybrid energy storage system and energy demand reduce carbon emissions by 78.69%, improve cost savings by 23.5%, and improve renewable energy utilisation by over 13.2% compared to other baseline models; and (ii) the proposed algorithm outperforms the state-of-the-art self-learning algorithms like the deep-Q network., This work was supported by the Smart Energy Network Demonstrator project (grant ref. 32R16P00706) funded by ERDF and BEIS. This work is also supported by the EPSRC EnergyREV project (EP/S031863/1) and the Horizon Europe project i-STENTORE (101096787) and FNR CORE project LEAP (17042283). This research received no external funding., Peer Reviewed, Postprint (published version)

©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., The high penetration of distributed energy resources, based on power electronics, is giving rise to stability issues in the electrical network, as initially those plants were not required to provide either voltage or frequency support. Due to this, transmission system operators (TSOs) and distribution system operators (DSOs) have set new requirements for them to provide grid support functionalities. This article presents a grid forming control strategy for power converters which is based on a virtual admittance loop. By means of this strategy it is possible to use a conventional current control based inverter, just adding this outer loop. By doing so, the converter is not only able to perform current control, but also frequency and voltage support functionalities. In this article, the proposed control is described and analyzed, checking as well its stability boundaries. After this analysis, the results obtained in a hardware-in-the-loop platform, where faulty scenarios, islanding or black start conditions, will be shown. Finally, the results obtained in an experimental true scale workbench will show its effectiveness for providing such services., This work was supported in part by LC-SC3-ES5-2018-2020-INTERRFACE project under Grant GA 824330 and in part by FlexiGRID project under Grant RTI2018-100921-B-C21., Peer Reviewed, Postprint (author's final draft)

Aquest projecte té com a objectiu principal calcular el guany d’energia mig que es podria esperar d’un sistema fotovoltaic integrat al sostre i altres parts del vehicle elèctric per tal de reduir la càrrega de xarxa. En funció del perfil del consumidor final i, per tant, de l'ús que li fa al vehicle, es veurà quin percentatge d’energia pot cobrir el sistema implementat. Es combinen els sectors del transport i de les energies renovables amb el propòsit de desenvolupar i apostar per tecnologies poc integrades en l’actualitat, però que donaran solucions a problemes futurs, especialment relacionats amb la mobilitat elèctrica. L’interès per aquest projecte neix com a conseqüència d’haver començat a treballar en el sector de l’energia fotovoltaica juntament amb la intenció de contribuir amb el medi ambient per construir un futur més sostenible. El primer pas ha consistit en descriure l’estat actual d’ambdós sectors, on s’introdueix al lector la problemàtica ambiental actual i com grans entitats comencen a establir objectius per el canvi cap a un futur verd, invertint i aplicant mesures correctores. A continuació, s’ha desenvolupat un bloc teòric on s’expliquen el aspectes més rellevants tant de l’energia fotovoltaica com els del vehicle elèctric. Un cop contextualitzada la situació, s’ha procedit amb la realització d’una simulació digital amb el programari PVsyst. Un cop obtinguts uns resultats favorables, s’ha procedit a la simulació física del projecte. Per a fer-ho, s’ha emprat una càrrega programable per a simular el vehicle en si, i també dues plaques fotovoltaiques. Tots els materials necessaris han estat cedits per Disolar i el SEER. Tot seguit, s’ha procedit a la recopilació de les dades obtingudes. Per finalitzar, un cop analitzades les dades, es pot afirmar que el sistema implementat pot arribar a cobrir un percentatge igual a 33% en el millor dels casos pel vehicles particulars i respecte als vehicles comercials un 16% , sent aquesta una xifra important del con

A la portada consta el nom del programa interuniversitari: Joint Doctoral Programme in Electric Energy Systems [by the] Universidad de Málaga, Universidad de Sevilla, Universidad del País Vasco/Euskal Erriko Unibertsitatea i Universitat Politècnica de Catalunya, Power system is undergoing an unpreceded paradigm shift: from centralized to distributed generation. As the renewable-based generations and battery storage systems are increasingly displacing conventional generations, it becomes more and. more difficult to maintain the stability and reliability of the grid by using only conventional generations. The main reason for the degradation of grid stability is the rapid penetration of nonconventional sources. These new generations interface with the grids through power electronics converters which are conventionally designed to maximize conversion efficiency and resource utilization. Indeed, these power converters only focus on their internal operation despite the grid conditions, which often worsens the grid operation. To overcome such a drawback, the grid-forming concept has been proposed for power converters, aiming to redesign the control of the power converters to enforce more grid-friendly behaviours such as inertia response and power oscillation damping to name a few. Despite the rich literature, actual adaptation of grid-forming controller in real-world applications is still rare because incentives for renewable power plants to provide services based on such advanced grid-forming functions were at best scarce. In the last years, however, several system operators have imposed new requirements and markets for grid-supporting services. In addition, the existing grid-forming controllers require modification to low-level control firmware of a power converter, which is often unrealistic due to the control hardware limitations as well as necessary testing and certifications. To ensure a stable operation of a grid-forming converter under adverse operating conditions, a robust voltage sensorless current controller is developed in this PhD thesis. The proposed controller is able to handle most of the possible abnormal conditions of the grid such as impedance variations, unbalanced voltage; harmonics distortion. These abnormali, A medida que las generaciones basadas en energías renovables y los sistemas de almacenamiento de baterías desplazan la generación convencional, se vuelve cada vez más difícil mantener la estabilidad y confiabilidad de la red. Estas nuevas generaciones interactúan con las redes a través de convertidores de electrónica de potencia que están diseñados tradicionalmente para maximizar la eficiencia de conversión y la utilización de recursos. Estos convertidores centran su funcionamiento interno independientemente de las condiciones de la red, lo que a menudo empeora el funcionamiento de la red. Para esto, se ha propuesto el concepto de convertidores de potencia formadores de red (grid-forming), con el objetivo de rediseñar el control de los convertidores de potencia para imponer comportamientos más favorables a la red, por ejemplo, la respuesta inercial y la amortiguación de oscilaciones de potencia. No en tanto, la adaptación real del controlador grid-forming en aplicaciones del mundo real todavía es escasa debido a los pocos incentivos para que las plantas de energía renovable proporcionen servicios basados en funciones de formación de red tan avanzadas. Aunque en los últimos años, operadores de sistemas han impuesto nuevos requisitos y mercados para servicios auxiliares, los controladores grid-forming existentes requieren cambios en el firmware de control de bajo nivel de un convertidor de potencia, algo poco realista debido a las limitaciones del hardware de control, así como a las pruebas y certificaciones necesarias. En esta tesis se desarrolla un controlador de corriente robusto, sin sensor de tensión, para garantizar el funcionamiento estable de un convertidor grid-forming en condiciones de operación adversas. Este controlador es capaz de manejar la mayoría de las condiciones anormales de red, como variaciones de impedancia, tensión desequilibrada y distorsión de armónicos. Estas anomalías de la red se representan matemáticamente mediante modelos lineales equival, Postprint (published version)

As penetration of photovoltaic (PV) and wind generation systems driven by grid-connected power converters monotonously increases, unusual interactions between innovative and legacy generation systems become more concerning, since they threaten the system stability and reliability. These undesirable interactions are mainly due to the fact that power converters and conventional electromechanical generators currently work under different physical and control principles and rules. This gives rise to some incompatibilities in terms of dynamic response and physical limits, which has become evident once the share of power converters connected to the grid has become relevant enough. In order to address this issue, this chapter presents some relevant concepts for implementing grid-following and grid-forming power converters. In this way, after reviewing some basis on PV and wind generation, this chapter discusses about the operation principle of such power converters, reviewing some fundamentals on grid synchronization strategies and current controllers. After that, some control schemes for gird-forming converters will be presented, paying particular attention to the role of droop control loops and the virtual impedance control. Finally, a general introduction of the synchronous power controller is provided as a preferred implementation of a grid-forming converter based on the virtual synchronous machine concept., Peer Reviewed, Postprint (published version)

El present treball de fi de grau té com a motivació el disseny i creació d'una central electrònica de connexions que permeti el control del circuit secundari dels sistemes de climatització per terra radiant. Aquest treball engloba el procés complet de crea ció d'un prototip, des de l'estudi del la viabilitat d'inclusió en el mercat fins a la creació d'una unitat física funcional. benchmark i de Aquest prototip inclou una sèrie de millores respecte a la gran majoria de centrals del sector, aprofitant així un gran nínxol de mercat on destacar per la seva eficiència i funcionalitat a un cost assequible per projectes i instal·lacions de grans magnituds. Per tal d'aconseguir resultats favorables s'ha estructurat el desenvolupament del projecte en diversos paquets de treball per pautar el procediment a realitzar. Aquests paquets de treball comprenen la formació en el sector i l'estudi de mercat, l'anàlisi dels aspectes i funcionalitats a incloure en el prototip i el disseny previ, la simulació del funcionament dels diferents circuits, el disseny del circuit imprès i finalment la creació i muntatge de la central de connexions.Finalment, s'obtindrà un prototip real preparat per ser exposat a l'empresa Global Piping Systems S.L. del grup AC Fix per tal de ser acceptat, inclòs a la seva gamma de productes i portat a la producció i a la incorporació en el mercat de la mà d'una empresa de presència internacional i una potent inversió en el desenvolupament i distribució de sistemes de calefacció i refrigeració per terra rad iant. També s'obre la porta a l'ampliació d'aquest prototip enfocant la seva direcció en la digitalització de la gestió dels senyals manipulats i la seva possible combinació amb sistemes de captació solar

During the last decade, the penetration of grid-connected RES systems has been in constant increase, forcing those systems interfaced to the electrical grid to improve and design new advanced controllers to maintain the power converter under control. The most extended control for grid-tied inverters is the so-called grid-following control. This structure allows the system to regulate the power exchange to the grid by means of following the electrical grid phase and magnitude. However, on a general basis, this algorithm does not provide any support to the electrical grid during faults, decreasing the overall stability of the system. Over the last few years, virtual synchronous machines (VSM) have been introduced into the power converter control, emulating the behavior of a synchronous generator and creating the so-called grid-forming power converter. This paper proposes a voltage sensor-less synchronous fault compensator that provides some of the synchronous generator features exclusively during transients., Peer Reviewed, Postprint (published version)

El subministrament d’electricitat de Nigèria es caracteritza principalment pel seu enorme dèficit. A prop del 50% de la població no té accés a la xarxa elèctrica, i els talls de corrent i caigudes de potència resulten extremadament perjudicials per l’economia del país. En aquest context, els centres de salut en zones rurals, tot èssent edificis crítics, pateixen constantment les conseqüències de la manca d’una xarxa elèctrica que arribi fins les zones més inaccessibles. El present projecte pretén demostrar com, a través dels estàndards definits pel disseny de centres de salut a Nigèria, es pot arribar a definir una solució tipus d’instal·lació off-grid aplicable a qualsevol projecte de construcció de centre de salut del país, promovent d’aquesta forma els sistemes off-grid com a solució òptima per les zones rurals. El projecte també proposarà la utilització de programes de modelització de xarxes elèctriques, així com “digital twins” per augmentar l’eficiència a les fases de disseny i construcció dels centres de salut. Finalment, la integració de la instal·lació off-grid amb sistemes de gestió integral d’edificis, els coneguts “Building Management Systems” permetrà disposar d’informació sobre l’edifici a temps real i monitoritzar els consums, de forma que es podrà augmentar de forma substancial l’eficiència energètica del centre., Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.a - Per a 2030, augmentar la cooperació internacional per tal de facilitar l’accés a la investigació i a les tecnolo­gies energètiques no contaminants, incloses les fonts d’energia renovables, l’eficiència energètica i les tecnologies de combustibles fòssils avançades i menys contaminants, i promoure la inversió en infraestructures energètiques i tecnologies d’energia no contaminant

Tesi elaborada dins del Joint Doctoral Programme in Electric Energy Systems, Most of large scale photovoltaic systems are based on centralized configurations with voltage source converters of two or three output voltage levels connected to photovoltaic panels. With the development of multilevel converters, new possible topologies have come out to replace current configurations in large scale photovoltaic applications, reducing filter requirements in the ac side, increasing the voltage level operation and improving power quality. One of the main challenges of implementing multilevel converter in large scale photovoltaic power plants is the appearance of high leakage currents and floating voltages due to the significant number of power modules in series connection. To solve this issue, multilevel converters have introduced high or low frequency transformers, which provide inherent galvanic isolation to the photovoltaic panels. The Cascaded H-Bridge converter (CHB) with high frequency transformers in a second conversion stage has provided a promising solution for large scale application, since it eliminates the floating voltage problem and provides an isolated control stage for each dc side of the power modules. In an effort to integrate ac transformers to reduce the requirement of a second conversion stage, Cascaded Transformer Multilevel Inverters (CTMI) have been propose for photovoltaic applications. These configurations use the secondary side of the ac transformers to create the series connection, while the primary side is connected to each power module, satisfying isolation requirements and providing different possibilities of winding connections for symmetrical and asymmetrical configurations. Based on the requirements of multilevel converters for large scale photovoltaic applications, the main goal of this PhD dissertation is to develop a new multilevel converter which provides galvanic isolation to all power modules, while allowing an independent control algorithm for their power generation. The configuration proposed is called Isolate, La mayoría de los sistemas fotovoltaicos de gran escala tienen una configuraci ón centralizada con convertidores de dos otres niveles de tensión de salida conectados a paneles fotovoltaicos. Con el desarrollo de los convertidores multinivel, nuevas topologías han aparecido para reemplazar las configuraciones usadas actualmente en aplicaciones fotovoltaicas, reduciendo los requerimientos de grandes filtros, incrementando los niveles de tensi ón de operación y mejorando la calidad de la potencia. Uno de los mayores desafíos de los convertidores multinivel en aplicaciones fotovoltaicas de gran escala es la presencia de corrientes de fuga y tensiones de flotación debido al significante aumento de módulos de potencia conectados en serie. Para solucionar este problema, los convertidores multinivel incluyen transformadores de alta o baja frecuencia, los cuales proveen aislación galvánica a los paneles fotovoltaicos. El Convertidor Cascada con Puente H y transformadores de alta frecuencia en una segunda etapa de conversión ha proporcionado una solución prometedora para aplicaciones de gran escala, ya que elimina el problema de tensión de flotación y además proporciona una etapa de control independiente al bus dc. En un esfuerzo de integrar transformadores en el lado de corriente alterna para evitar una segunda etapa de conversión, los Convertidores Multinivel con Transformadores en Cascada (CTMI) han sido propuestos para aplicaciones fotovoltaicas. Estas configuraciones utilizan el secundario del transformador para crear la conexi ón serie, mientras que el primario es conectado a cada módulo de potencia, satisfaciendo los requisitos de aislaci ón y proporcionando diferentes posibilidades de conexiones en los devanados para generar configuraciones sim étricas y asimétricas. Considerando los requisitos de convertidores multinivel para aplicaciones fotovoltaicas de gran escala, el principal propósito de esta tesis es desarrollar una configuración de convertidor multinivel el c, Postprint (published version)

The proliferation of grid-connected converter interfaced energy sources in Smart Grids, enhance sustainability and efficiency as well as minimizing power losses and costs. However, concerns arise regarding the stability and reliability of future smart grids due to this wide integration of power electronic devices, which are recognized to affect the dynamic response of the system, especially during disturbances. For instance, apart from the lower damping of existing electromechanical modes, new low-frequency oscillations begin to appear. Yet, the ability of grid-connected converters to provide grid support functionalities can alleviate the aforementioned challenges. Relevant studies show that these functionalities can be enhanced even further, if information regarding the oscillation characteristics are available. Traditional methods for extracting modal information are very well suited for monitoring purposes, however, they pose certain limitations when considered for control applications. Therefore, this paper proposes a multi-band intelligent power oscillation damper (MiPOD) that exploits 1) the inherent characteristics of grid-connected converters to damp multiple power oscillations and 2) the modeling capabilities of Artificial Intelligence (AI) for predicting the frequency of electromechanical oscillations in the system, as operating conditions change. Essentially, the MiPOD integrates the AI model in the control loop of the converter to attenuate multiple modes of oscillation. The proposed controller is validated for different disturbances and randomly generated operating points in the two area system. Specifically, in this case the AI model is a Random Forest ensemble regressor that is developed for tracking two electromechanical modes. As it is shown, the MiPOD can improve the overall performance of the system under various contingency scenarios with only 6% of the corresponding total nominal capacity of synchronous generators. In addition, the monitoring an, This work was supported by the European Commission under project INTERFACE - H2020-LC-SC3-2018-ES-SCC-824330 and by the Spanish Ministry of Science under project ENE2017-88889-C2-1-R., Peer Reviewed, Postprint (published version)

The integration of renewable energies based on photovoltaic power plants (PVPPs) is increasing exponentially fast. In consequence, stability problems associated with the lack of inertia are becoming a serious concern. Transmission and distribution system operators are demanding more requirements in PV plants to provide grid functionalities in terms of frequency and voltage support. Therefore, power converters based on virtual synchronous controllers have been proposed to emulate the dynamic behavior of synchronous generators. Control strategies such as the synchronous power controller have been proposed for PV applications to fulfill this requirement. However, most of these control strategies are integrated locally as an add-on firmware embedded in each converter, providing the demanded support in their connection point. For PVPPs, the inherent synchronous characteristic is expected at the connection point with the electrical grid, which is not always the connection point of each power converter; thus, unexpected power support levels can be obtained. The aggregation of several power converters operating in a coordinated synchronous action would solve this issue, due to the fact that they can provide voltage and frequency support in a specific point. In this article, a centralized control strategy based on a synchronous central architecture is proposed. The control strategy emulates an aggregated synchronous control to regulate a PVPP as a coordinated system. The simulation and experimental results validate the effectiveness of the control proposed., Peer Reviewed, Postprint (author's final draft)

En este proyecto se plasma el diseño y desarrollo de un sistema, robusto, escalable y a prueba de fallos, de monitoreo energético a partir de diversas componentes eléctricas, como la tensión, corriente, potencia activa y reactiva, basado en Iot (Internet of Things). Para la captura de la información se plantea el uso de un analizador de energía de la gama PowerLogic PM8000 series, que permite obtener las mediciones que este proyecto requiere y más, posibilitando su uso en futuros proyectos basados en este trabajo. La información obtenida tiene el objetivo de ser utilizada para detectar ineficiencias en el consumo, aproximar un perfil de uso eléctrico y dimensionar y gestionar una instalación de producción eléctrica alternativa. Con este fin, en este trabajo se considera una programación de un dispositivo local para gestionar la información de diversos analizadores energéticos, en este trabajo se utilizará uno solo, la fiabilidad de los protocolos y medios físicos de comunicación, y una estructura eficiente, fácilmente escalable y replicable, a la vez que adaptable. Se plantea un sistema de comunicaciones que permita la visualización de los datos de manera remota, a través de internet. Por tanto, se plantea el uso de un Raspberry pi como dispositivo local, por us capacidad de procesado y conexión de red física e inalámbrica. Éste se comunicará mediante protocolo MQTT (Message Queue Telemetry Transport) a una plataforma SaaS(Service as a Software) de AWS(Amazon Web Service) donde se almacenará la información en una base de datos para su posterior visualización y tratado a través de la API (Application Programming Interface) con la posibilidad de crear alarmas y/o reglas de control para sistemas colaterales. Con esta estructura basada en código propio, el uso del SaaS y la posibilidad de uso de dispositivos de bajo coste, análogos a los definitivos, en el diseño y desarrollo, permite que se realizaran ambos con una gran eficiencia de calidad frente a coste económico. D

With the advent of renewable energy, stability of power system is becoming more and more crucial. Recently, grid-forming converter concept has attracted much attention from the industry and academia as a potential solution to improve power system stability. This paper proposes a frequency-selective power oscillation damper for grid-forming power converter to improve its flexibility and performance in damping electromechanical modes. The proposed controller employs the multi-rotor concept where a virtual synchronous machine with multiple rotors is emulated in the control part of a grid-forming power converter. In addition to the enhancement in suppressing power oscillation, the main advantages of the proposed controller include the ability to provide the damping selectively for each electromechanical mode. That is, the proposed controller allows setting the desired damping individually for each oscillation mode. The performance of the proposed controller is validated by using the three-machine infinite bus system., This work was supported by the European Commission under the project FLEXITRANSTORE - H2020-LCE-2016-2017-SGS-774407, Peer Reviewed, Postprint (published version)

This paper proposes a management strategy based on a transactive mechanism to improve the efficiency of energy storage systems. The proposed control scheme relies on a non-cooperative strategy where each system is at the liberty to set its price in order to maximize owner profit while maintaining power system stability. The novelty of this approach comes from the simple yet effective design of the management strategy. In fact, different from existing works, the proposed management scheme is treated in the framework of classical control which does not only result in reliable implementation but also is easy to be incorporated in stability studies. Simulation and experimental results of a utility-scale battery energy storage system are provided to validate the effectiveness of the proposed management strategy., This work was supported by the European Commission under the project FLEXITRANSTORE H2020-LCE-2016-2017-SGS-774407 and the project INTERRFACE H2020-LC-SC3-2018-ES-SCC - GA 824330., Peer Reviewed, Postprint (published version)

El presente proyecto tiene como objetivo, el estudio de la viabilidad tanto técnica como económica de una instalación fotovoltaica para autoconsumo o venta de esta energía, en la fábrica SENSOFAR GROUP, situada en el recinto del Parque Audiovisual de Terrassa. Debido a la evolución y reducción de costes que ha experimentado esta tecnología, cada vez son más empresas y usuarios particulares que optan por implementar estos sistemas en sus edificios y hogares, con el fin de reducir los costes por consumo eléctrico, y promover e impulsar una transición tecnológica verde. Para el correcto dimensionado de la instalación que se llevará a cabo, se utilizarán una serie de análisis y cálculos que ayudaran a escoger los componentes eléctricos y electrónicos, entre otros, así como una correcta colocación y distribución de los paneles fotovoltaicos, que maximice la producción y a su vez, que se minimicen las pérdidas por sombreado. Conjuntamente, se analizará el emplazamiento y lugar geográfico, clima de la zona mediante bases de datos e históricos hasta la actualidad, y se construirá un modelo 3D del edificio que nos permita elaborar un estudio de sombras. Todos estos cálculos y estudios se respaldarán por simulaciones, a través del software especializado PVsyst, el cual generará un informe con el que podremos comprobar de forma mucho más extensa diferentes parámetros y características del sistema planteado. Dichos resultados serán de gran ayuda para consolidar las decisiones y cálculos, que se habrán desarrollado a lo largo del proyecto. Finalmente, se implementará un estudio económico, donde se mostrará la rentabilidad económica del proyecto, de la mano de presupuestos y balances económicos.

Donada la situació d’emergència climàtica que actualment viu el planeta Terra cal buscar noves fonts d’energia que permetin suplir el seu consum de manera responsable amb el medi ambient. Aquest fet sumat a les constants pujades de preu del mercat elèctric converteix les instal·lacions d’autoconsum en un imperatiu dels nous temps que venen. En aquest treball s’exposen aquestes causes i s’estudien les instal·lacions fotovoltaiques, des dels seus elements fins la seva regularització, per acabar dissenyant dues plantes fotovoltaiques per dos edificis propietat de la Universitat Politècnica de Catalunya: El TR8-FOOT i el TR30-CUV. Ambdós situats enfront l’altre al municipi de Terrassa. L’objectiu final d’aquest treball es analitzar la viabilitat real de la implementació d’aquestes instal·lacions.

During the years, grid connected operation in power systems has been the key factor for renewable energy resource to be able to exchange energy to the electrical grid. However, with the increase of small power systems and micro-grids, the standalone operation and the blackstart of the power system has been increasingly considered a demand in most of power converters connected to the micro-grid system. The gridforming power converter strategy has been widely used in micro-grid scenarios, taking the virtual synchronous machine concept behind it. This emulation of a synchronous machine benefits the power converter with additional features, such as island operation or blackstart. In this regard, this paper presents a resynchronization system for a grid-forming power converters, based on the synchronous power control, the match the phase angle of the utility grid prior to its connection., This project has been partially funded by Spanish Ministry of Science Innovation and Universities under the project RTI2018-100921-B-21 and the H2020-LC-SC3-2018-ES-SCC project Interrface GA824330., Peer Reviewed, Postprint (published version)

Grid-forming power converters (GFMC) have been widely adopted in power systems as an attractive solution against the challenges imposed by the ever-increasing penetration of renewables. Despite its versatility, GFMC is employed only to provide islanded operation, grid regulations, and synthetic inertia. To further extend the use of GFMC in enhancing power system stability, this paper proposes a multi-rotor virtual machine (MRVM) controller to attenuate sub-synchronous oscillations. Driven by the formulation of a virtual synchronous machine (VSM), the proposed MRVM implements a VSM-based GFMC with several virtual rotors whose electromechanical characteristics can be individually adjusted to target specific oscillatory modes in the system. In this work, the MRVM’s working principle is described in detail and tuning guidelines are proposed to simplify the selection of control parameters by using frequency-domain techniques and the eigenvalue locus analyses. To validate the performance of the MRVM, an IEEE benchmark grid model is adopted namely, the three-machine-infinite-bus system. It is evident from the results that the MRVM (i) provides higher degrees of freedom when dealing with sub-synchronous oscillations, and (ii) outperforms conventional GFMC, especially in damping intra-area power oscillations., This work was supported by the European Commission under Project FLEXITRANSTORE-H2020-LCE-2016-2017-SGS-774407., Peer Reviewed, Postprint (published version)

The advent of renewable energy has posed difficulties in the operation of power systems whose net inertia is becoming critically low. To face such challenges, grid-forming power has been one of the potential solutions pursued by the industry and research community. Although promising, grid-forming power converters are still immature for mass deployment in power systems. In the meanwhile, an enormous amount of grid-following power converters has been underexploited when it comes to grid-supporting functionalities. Therefore, this article proposes an external inertia emulation controller (eIEC) for grid-following power converter to provide frequency support to the grid. For the purpose of minimizing installation efforts and resources, the controller is designed in such a way that it can be implemented in an external controller communicating with the grid-following power converter via an industrial communication link. This article also investigates the effect of communication delay on the stability performance of the proposed controller. In addition to the detailed analysis, hardware-in-the-loop experiments are also carried out to validate the proposed eIEC., This work was supported by the European Commission under Project FLEXITRANSTORE-H2020-LCE-2016-2017-SGS-774407, Peer Reviewed, Postprint (author's final draft)

Series connections of modules in cascaded multilevel converters are prone to power imbalances due to voltage differences on their DC side. When modules are connected to direct current (DC) sources, such as photovoltaic panels, the capability of withstanding power imbalances is crucial for generating the maximum power. In order to provide a possible solution for this requirement, this paper proposes a control strategy called Quadrature Voltage Compensation, which allows a wide range of power imbalances. The proposed control strategy regulates the power by introducing a circulating current between the arms and a phase angle in the output voltage. The impact of the circulating current and its effect on the phase voltage are studied. To highlight the features of the proposed strategy, an analytical model based on vector superposition is also described, demonstrating the strong capability of tolerating power differences. Finally, to validate the effectiveness of the Quadrature Voltage Compensation, simulation and experimental results are presented for a three-phase isolated multi-modular converter., This work was supported by the Ministry of Science Innovation and Universities under the project RTI-2018-100921-B-21 and by the European Commission under the projects FLEXITRANSTORE H2020-LCE-2016-2017-SGS-774407 and INTERRFACE H2020-LC-SC3-2018-ES-SCC-824330., Peer Reviewed, Postprint (published version)

El presente Trabajo de Fin de Grado consiste en la elaboración de un prototipo de sistema basado en tecnología IoT para la monitorización y supervisión de cambios de agujas o desvíos en los sistemas ferroviarios, instalaciones críticas en cuanto a la seguridad de la circulación de trenes. Para ello, se estudia, en primer lugar, la estructura de los cambios de agujas y se definen los parámetros a monitorizar para garantizar la integridad de estas instalaciones. A continuación, se establecen las herramientas necesarias para el diseño de un sistema IoT que permita monitorizar este tipo de instalaciones, así como las distintas opciones existentes para cada una de ellas, eligiendo en cada caso aquella que mejor se adapta a los requerimientos del proyecto. En la parte central del trabajo, se lleva a la práctica el sistema estudiado, mediante la realización del prototipo mencionado, incorporando todos los elementos estudiados. Por último, se demuestra la funcionalidad del prototipo en su totalidad y la posibilidad de la creación de una solución similar, basado en el prototipo, que se podría implementar en un entorno real.

Emulating inertia using power converter has been an effective way to provide additional inertia to power electronic dominated power systems. Currently, the control algorithms for emulating inertia have been proposed considering embedded implementation meaning that control algorithms are implemented in digital controller of power converter. However, it is not always feasible or cost-effective to upgrade control firmware of power converters. On the other hand, most of commercial power converter are equipped with at least one fieldbus interface, which can be employed for control purposes. This paper explores the possibility of emulating inertia by means of an external controller, which communicates with power converter via a communication link. Detailed analyses, especially regarding the influence of communication delays on the system stability and on performance indices such as RoCoF and frequency nadir, are given to provide insight into such an external implementation. The proposed implementation approach are also validated through simulations and hardware-in-the-loop (HIL) experiments., This work was supported by the European Commission under project INTERRFACE - H2020-LC-SC3-2018-ES-SCC– 824330 and by the Spanish Ministry of Science under project ENE2017-88889-C2-1-R., Peer Reviewed, Postprint (published version)

Synchronization plays a fundamental role in connecting power electronic converters with the grid. Conventionally, the synchronous reference frame phase-locked loop (SRF-PLL) has been widely used to estimate the grid phase angle. Though SRF-PLL is effective under normal grid voltage conditions, its performance degrades drastically under weak grid conditions. This paper presents a control strategy for current controller of grid-connected power converters that contributes in the reduction of the negative effects of SRF-PLL during grid disturbances. The main control concept is based on virtual admittance. This approach is capable of operating effectively power converters when connected to weak grids and permit grid-forming operation. Simulation and experimental results are provided to validate the proposed controller., This project has been partially funded by Spanish Ministry of Science Innovation and Universities under the project RTI2018-100921-B-21 and the H2020-LC-SC3-2018-ES-SCC project Interrface GA824330., Peer Reviewed, Postprint (published version)

Renewable energy and battery energy storage systems are affecting the dynamics of power systems mainly due to the interconnection through power electronics with the electric grid. Specifically, the low inertia characterizing these systems impact’s the overall rotor angle stability of the power electronics dominated power systems. Hitherto, power system stabilizers are the common approach to mitigate electromechanical oscillations, which their parameters are tuned rarely resulting to sub-optimal performance against the changing conditions. In this paper, intelligent power oscillation damper (iPOD) is proposed for grid-forming power converters to attenuate sub-synchronous oscillations. The iPOD is tuned to the inter-area modes in realtime through an ensemble AI model based on Decision Trees called Random Forests. The proposed control scheme is verified using the two area system considering symmetrical faults as well as network variations. In addition, the damping capabilities of the proposed scheme are compared with the damping of the power system stabilizer installed in each generator., This work was supported by the European Commission under project INTERRFACE - H2020-LC-SC3-2018-ES-SCC- 824330 and by the Spanish Ministry of Science under project ENE2017-88889-C2-1-R., Peer Reviewed, Postprint (published version)

A grid-forming power converter based on the synchronous power controller (SPC) is a solution that through the flexible and adaptive emulation of the main functional blocks of a synchronous machine, allows to take advantage of its benefits while avoiding or minimizing its weaknesses. In this paper a small signal stability analysis of a grid-forming power converter based on SPC is performed. The analysis includes obtaining a representation of the system’s state space, calculating its eigenvalues and analysing the sensitivity to variation of some relevant parameters. Some simulations and experimental tests have also been carried out to validate the theoretical analysis., This work was supported by the European Commission under projects INTERRFACE H2020-LC-SC3-2018-ES-SCC824330 and by the Spanish Ministry of Science under project RTI2018-100921-B-C21., Peer Reviewed, Postprint (published version)

During the last decade the penetration of gridconnected RES systems has increased exponentially forcing power conversion industry to design new advanced controllers in order to comply with new requirements. The current control loop is a critical layer to improve the RES performance especially in weak grid and remote micro-grids. Based on the resonant control concept, this paper presents a modified structure for the PR controller which results advantageous when implemented on RES systems, as it allows the system to perform as a PI in the synchronous reference frame during the dynamic state of the controller. This paper also deals with the analysis of the decoupling terms in the stationary reference frame, which will add an improvement to the dynamic response of the controllers. The proposed controller will be analyzed, discussed and finally validated by means of simulation analysis, This work was supported by the European Commission under projects INTERRFACE H2020-LC-SC3-2018-ES-SCC824330 and by the Spanish Ministry of Science under project RTI2018-100921-B-C21., Peer Reviewed, Postprint (published version)

The integration of non-synchronous generation units and energy storage through power electronics is introducing new challenges in power system dynamics. Specifically, the rotor angle stability has been identified as one of the major obstacle with regards to power electronics dominated power systems. To date, conventional power system stabilizer (PSS) devices are used for damping electromechanical oscillations, which are only tuned sporadically leading to significant deterioration in performance against the ever-changing operating conditions. In this paper, an intelligent power oscillation damper (iPOD) is proposed for grid-forming converters to attenuate electromechanical inter-area power oscillation. In particular, the iPOD is applied to a synchronous power controller (SPC) based grid-forming power converter to increases gain of the active power control loop at the oscillatory frequency. Predictions regarding the mode frequency, corresponding to the current operating points, are given by an artificial intelligence ensemble model called Random Forests. The performance of the proposed controller is verified using the two area system considering symmetrical fault for random operating points. In addition, a comparison with PSS installed in each generator reveals the individual contribution with respect to the inter-area mode damping., This work was supported in part by the European Commission under Project FLEXITRANSTORE—-H2020-LCE-2016-2017-SGS774407, and in part by the Spanish Ministry of Science under Project ENE2017-88889-C2-1-R., Peer Reviewed, Postprint (published version)

The series-connection of modules in multilevel converters are prone to energy imbalances in the dc capacitor due to the differences between the power absorbed and consumed. In renewable energy applications where the primary source is directly connected to each module, energy imbalances can be even worse if the primary sources are affected by unpredictable weather conditions. Therefore, control strategies are required to compensate such energy imbalances, while maintaining the correct converter operation. Focusing our attention on a cascaded transformer multilevel inverter called Isolated MultiModular Converter, this paper introduces the combination of two control strategies aimed at providing a wide range of operation under imbalanced energy states. A general analytical model, including the regulation capability and differences with an existing strategy are presented to demonstrate the performance of the control proposed. The effectiveness of the proposal is validated through experimental results based on a three-phase multilevel prototype., This work was supported in part by the European Commission under Project FLEXITRANSTORE—H2020-LCE-2016-2017-SGS-774407 and Project INTERRFACE—H2020-LC-SC3-2018-ES-SCC-824330, and in part by the Spanish Ministry of Science under Project ENE2017-88889-C2-1-R., Peer Reviewed, Postprint (published version)

©2019 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 operators require grid connected RGUs to provide specific dynamic features. RGUs must support dynamic performance of grid and operate in such a way to ward off new issues in grid. Recently, unfavorable oscillatory modes have appeared through grid connection of RGUs due to their dynamic interaction with other classical components of grid. Therefore, it is essential to develop a novel technique for dynamic design of RGUs to mitigate such risky oscillations. In this paper, a novel analytical method is proposed for dynamic tuning of a RSSG-SPC. Proposed method is based on mathematical analysis of derivative function of general damping ratio formula. The analytical results establishes generalized solutions that cover all operation mode of RSSG-SPC. Further on, solutions are implemented into dynamic model of RSSG-SPC to obtain clear, accurate and trustable criteria for tuning of virtual damping and virtual inertia. The dynamic tuning aims towards avoiding new oscillations in system and to mitigate natural oscillations of grid. Proposed approach was used for stability enhancement in high penetrated generation area and to support synchronization between interconnected areas in Kundur system. Proposed method was validated through modal analysis, time domain simulations and real-time evaluations which ensured that proposed approach is a reliable technique for dynamic design of RSSG-SPCs., Peer Reviewed, Postprint (author's final draft)

The presence of power electronics in today’s power systems strengthens due to the wider integration of renewable energy and energy storage systems. Subsequently, the dynamical response becomes harder to model and understand. As a possible solution, coherency identification, among other applications, can reduce complexity. However, conventional tools possess limitations related to the assumptions need to be taken beforehand. In this paper, we propose a fully unsupervised variation of neural networks called the growing self organising maps (GSOM). The main advantage of GSOM over traditional methods is that network structure is not fixed, thus previous assumptions about the number of coherent groups or data structure are not necessary. A spreading factor controls the growth rate of the network allowing the analyst to choose the level of granularity whilst ensuring topology preservation. The effectiveness of the proposed algorithm is tested on the Nordic 32 power system., This work was supported by the European Commission under project INTERRFACE - H2020-LC-SC3-2018-ES-SCC– 824330 and by the Spanish Ministry of Science under project ENE2017-88889-C2-1-R., Peer Reviewed, Postprint (published version)

During the years, synchronization systems in power converter control has been mainly used for estimating the phase angle and the magnitude of the grid voltage, this estimated information is usually used for droop control strategies to ensure power sharing among power converters. Most of existing synchronization systems rely on the voltage measurements at the point of common coupling of the power converter, which may be distorted or unbalanced. This paper presents a voltage sensorless grid-forming structure for power converter in microgrids. By means of reading the voltage reference of the power converter, the system is able to synchronize with the grid. In addition, the virtual admittance compensation provides grid-forming capabilities to the power converter, which can emulate the inertia and damping of the synchronous machine in its synchronization structure, based on the power balance synchronization., This work was supported by the European Commission under projects INTERRFACE H2020-LC-SC3-2018-ESSCC-824330 and by the Spanish Ministry of Science under project RTI2018-100921-B-C21., Peer Reviewed, Postprint (published version)

Grid-connected power converters have been increasingly utilized to inject renewable energy into the grid. To reduce installation cost and the same time to increase system stability, this paper presents control design for grid-connected power converters with only current sensors. The proposed control scheme mainly consists of a state-feedback controller and a state observer. To guarantee the stability of the closed-loop system, linear matrix inequality approach is employed to obtain control gains. As opposed to the existing approaches, the proposed scheme offers superior dynamic performance under voltage sag. Such improvement is achieved by incorporating the internal model of proportional controller into the state-feedback controller. The effectiveness of the proposed controller is validated by simulations under various operating conditions., This work was supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 824330, project INTERRFACE H2020-LCSC3-2018-ES-SCC and by the Spanish Ministry of Science under project ENE2017-88889-C2-1-R., Peer Reviewed, Postprint (published version)

©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., This article presents a robust voltage sensorless control scheme to eliminate the need of line-voltage sensors in an LCL-filtered grid-connected inverter system. The proposed control scheme is based on an extended-state estimator structure which consists of a state feedback regulator and an estimator. The main contribution of this article relies on the utilization of the linear matrix inequality approach and the internal model principle to synthesis a robust control scheme that equips a grid-connected inverter with the ability to withstand grid disturbances. As opposed to the existing works, the proposed control scheme can simultaneously deal with all types of grid disturbances, such as grid voltage distortion, grid voltage imbalance, and grid impedance variations. The effectiveness of the proposed controller is highlighted through comparative simulation results and in-depth analyses. Experimental results are also given to validate the practicality of the proposed control scheme., This research was funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie, grant number 712949 and the Spanish Ministry of Economy and Competitiveness under the project RTI2018-100921-B-C21., Peer Reviewed, Postprint (author's final draft)

Grid-connected converters with primary frequency control and inertia emulation have emerged and are promising for future renewable generation plants because of the contribution in power system stabilization. This paper gives a synchronous active power control solution for grid-connected converters. As design considerations, the virtual angle stability and transient response are both analyzed, and the detailed implementation structure is also given without entailing any difficulty in practice. The analysis and validation of frequency support characteristics are particularly addressed. The 10 kW simulation and experimental frequency sweep tests on a regenerative source test bed present good performance of the proposed control in terms of showing inertia and droop characteristics, and the controllable transient response is also demonstrated., Peer Reviewed, Postprint (author's final draft)

© 2019 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., Renewable energies has shown to be a promising solution to improve the energy injected to the electrical network. However, the lack of inertia in such systems have proven to affect the grid stability, as those technologies operate as current controlled sources they not provide grid support functionalities. This issue has fostered the implementation of new control strategies to enable power plants to provide a coordinated action to support some inertia and damping into the system. Synchronous controllers have proven to be an excellent option for distributed renewable generation, which allows to emulate the inertia of a synchronous generators, having a better interaction between the power converter and the electrical grid. However, the implementation of such control strategies require power converter to be smarter and include advanced control algorithms. In this paper, a new control strategy to control different distributed generation units to have a coordinated action in front of the electrical grid is presented, reducing the cost of the power converter by extracting the synchronous control from the internal controller and replacing in by a central synchronous controller., Peer Reviewed, Postprint (author's final draft)

©2019 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 network clustering (NC) method for active distribution networks (ADNs). Following the outage of a section of an ADN, the method identifies and forms an optimum cluster of microgrids within the section. The optimum cluster is determined from a set of candidate microgrid clusters by estimating the following metrics: total power loss, voltage deviations, and minimum load shedding. To compute these metrics, equivalent circuits of the clusters are estimated using measured data provided by phasor measurement units (PMUs). Hence, the proposed NC method determines the optimum microgrid cluster without requiring information about the network’s topology and its components. The proposed method is tested by simulating a study network in a real-time simulator coupled to physical PMUs and a prototype algorithm implementation, also executing in real time., Peer Reviewed, Postprint (author's final draft)

©2019 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 stability is one of the main concerns in renewable energies. The lack of inertia and their low capability to provide frequency support has created the need for implementing new control strategies to solve this problem. In current networks, frequency and voltage support are performed through synchronous generators, which provide an inherent grid support due to the inertia presented in their mechanical rotors. Based on the same concept, renewable energies based on power converters have introduced synchronous controllers to emulate the dynamic behavior of synchronous generators and provide voltage and frequency support. However, most synchronous control strategies integrate their controllers as an add-on firmware embedded in each power converter, without presenting a coordinated synchronous performance when several converters operate in a PV power plant. The aggregation of several power converters operating with a coordinated synchronous response would be advantageous in these cases, since they can provide a harmonic response with an automatic power distribution when grid support is required. This paper presents a synchronous control strategy for photovoltaic power plants, which manages several power converters as an aggregated synchronous system., Peer Reviewed, Postprint (author's final draft)

This paper presents a Unified Power Flow Controller (UPFC) application of the Custom Power Active Transformer (CPAT); a power electronics integrated transformer which provides services to the grid through its auxiliary windings. The CPAT structure integrates three single-phase transformers into one shunt-series combining transformer. This integration empowers a sub-station with the capability of dynamically regulating the terminal voltage and current of a transformer through isolated power electronics converters. This paper investigatesthe CPAT’s capability to provide UPFC services which includes power flow control, reactive power compensation, voltage regulation and harmonics elimination. Simulations of the CPAT-UPFC with a stiff grid and a 5-bus power system demonstrates its functionality as an inter-bus couplingtransformer that provides the required grid services. Moreover, the impact of the CPAT-UPFC during load perturbations on the power system is investigated to further validate its transient and steady-state response. Furthermore, an experimental prototype reveals the operation of the three-phase CPAT-UPFC confirming its stable operation according to the theoretical expectations., Peer Reviewed, Postprint (author's final draft)

Multilevel converters are widely used in medium and high voltage applications. Their high performance, power quality, efficiency and smaller filters make them interesting for renewable energy distribution systems. In utility- scale photovoltaic plants, these topologies could provide multiple benefits since they are able to connect string of photovoltaic panels to independent modules. However, high floating voltages caused by high number of modules limit multilevel converters in medium and high voltage applications, since all of them are not suitable to provide isolation to each module. To offer a solution, this paper presents a novel multi-modular converter that provides multiple isolated modules connected in series through low frequency transformers to operate at medium voltage levels. This topology is able to achieve the power balancing between the connected modules and independently adjust the dc voltage of each module by means of controlling a circulating current which flows through the arms. Furthermore, the topology implemented in photovoltaic renewable energy systems and the control strategy required to regulate the circulating and the output current are presented. The main principle behind this concept and the performance of the converter are evaluated and validated through simulation and experimental results., Peer Reviewed, Postprint (author's final draft)

© 2019 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 scheme of grid-tied converters is often implemented in the dq-frame due to simplicity of design. However, with this transformation, there exists an inherent cross-coupling term between the d-and q-channels which is often compensated for by using a feed-forward term in the current-control loop. It is shown, by applying the generalized Nyquist criterion (GNC) to the dq-frame ac impedance of the converter, that the inclusion of this decoupling term, in fact, degrades the stability of the controller when increasing the bandwidth of the synchronous reference frame phase-locked loop (SRF-PLL). Harware-in-the-loop (HIL) experiments are also conducted and verify these results., Peer Reviewed, Postprint (author's final draft)

© 2019 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., Synchronous power controller (SPC) has emerged as a suitable technique to equip grid-connected inverters with grid supporting functionalities such as inertial emulation and frequency/voltage support by mimicking the behavior of synchronous machines. Although the feasibility of the SPC has been experimentally verified under various operating conditions, parameter tuning for the SPC to ensure a stable inverter system has not been adequately addressed in the literature. To fill this gap, this paper presents a robust control design for the SPC to ensure its stable operation under the grid impedance variation. The proposed design procedure consists of system modelling and robust optimal parameter selection by using linear matrix inequality approach. The effectiveness of the proposed control design is proven by means of simulations and experiments., Peer Reviewed, Postprint (author's final draft)

The variable and unpredictable behavior of renewable energies impacts the performance of power systems negatively, threatening their stability and hindering their efficient operation. Flexible ac transmission systems (FACTS) devices are able to emulate the connection of parallel and series impedances in the transmission system, which improves the regulation of power systems with a high share of renewables, avoiding congestions, enhancing their response in front of contingencies and, in summary, increasing their utilization and reliability. Proper control of voltage and current under distorted and unbalanced transient grid conditions is one of the most critical issues in the control of FACTS devices to emulate such apparent impedances. This paper describes how the synchronous power controller (SPC) can be used to implement virtually synchronous FACTS. It presents the SPC functionalities, emphasizing in particular the importance of virtual admittance emulation by FACTS devices in order to control transient unbalanced currents during faults and attenuate harmonics. Finally, the results demonstrate the effectiveness of SPC-based FACTS devices in improving power quality of electrical networks. This is a result of their contribution to voltage balancing at point of connection during asymmetrical faults and the improvement of grid voltage quality by controlling harmonics flow., Postprint (published version)

In this paper a small signal stability analysis of a reverse droop-controlled grid-connected voltage source converter has been performed. The analysis includes the getting of a state-space representation of the system and the calculation of their participation factors. Special emphasis has been given to the influence of parameters such as the short circuit ratio, the bandwidth of the phase-locked and the constants of the droop controllers on the stability of the system., Postprint (published version)