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© 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, Learning-based state estimators can represent a cost-effective opportunity for distribution system operators to perform grid monitoring and control in low-voltage grids where the measuring infrastructure is minimal, if not absent. This study lays the foundation for designing and evaluating neural network-based state estimators for low-voltage radial distribution grids. A simulation-based methodology is proposed for generating synthetic training data-sets relying only on minimal grid data. Additionally, a novel framework for performance analysis of low voltage learning-based state estimators is considered, which relies on a bi-dimensional evaluation of the absolute error and the parallel observation of relative metrics. The applicability and potential of these estimators have been tested and validated through various low-voltage radial case studies, showing promising results especially for large distribution grids. Finally, a propagation error study has been conducted to observe how these estimators handle errors in input measurements., This work was supported in part by MCIN/AEI/10.13039/501100011033 under Project MERIDIAN TED2021-131753B-I00, and in part by the European Union ‘‘NextGenerationEU/PRTR.’’ The work of Andreas Sumper was supported by the Catalan Institution for Research and Advanced Studies (ICREA) Academia Program., Postprint (published version)

In remote areas of Sub-Saharan Africa, as well as in Rwanda, communities face the problem of finding an affordable and suitable way of transport for their daily life. Currently, the short-range transportation of people and goods rely on manual traction (e.g., bicycles, handmade wooden bicycle, etc.) and on small combustion engines. However, this region has a large renewable energy source (solar) which can help to mitigate this problem. Electric bicycles may be used to tackle the problem, although their use is still not largely widespread despite its potential. In addition, the local society does not have an easy way to accurately estimate the amount of energy consumed for a certain itinerary to be sure of how the electric vehicles perform. Thus, characteristic analysis of consumed energy is very important to analyze the performance of electric vehicle storage systems, model charging infrastructure, size vehicles, planning for itineraries, etc. This paper presents a methodology to estimate the power consumed by electric bikes for specific itineraries. In order to accomplish so, the WebPlotDigitizer tool and Google Maps were used to produce driving profile patterns. The results are compared against experimental data, showing the accuracy of the methodology presented. The simulated results show that the consumed power value differs by only 1.68% from the experimental recorded value; the difference can be explained by traffic congestion, the density of traffic, and the intersection that occurred during the experiment. The presented method of driving energy requirement estimation using WebPlotDigitizer is attractive, affordable, and easy to use., This study supported by; University of Rwanda (UR_CST) African Center for Excellence Energy for Sustainable Development, Mechanical and Energy Engineering Department., Peer Reviewed, Postprint (published version)

The increase in renewable energy sources and new technologies such as electric vehicles and storage can generate uncertainties in distribution grid operations, increasing the likelihood of congestions in power lines. Distribution system operators (DSOs) face several challenges while operating their grids in such conditions. These congestions deteriorate the electrical equipment in the long term, reducing its life span. This work proposes a framework to predict grid asset congestions on a daily basis. A congestion forecast framework is proposed by combining probabilistic power flows and machine learning algorithms to support DSOs in their daily decision-making. The framework is tested on a modified IEEE-33 bus system and CINELDI MV Reference system with hourly synthetic data. The results showed that the framework is able to closely predict the congestions on the lines. Computational capabilities are reported and discussed. The study indicates that the framework is a suitable tool for day-to-day congestion predictions in smart distribution grids yielding low error in expected values., The authors would like to thank Rubi Rana for discussion regarding the CINELDI Reference System. This work was supported by the project consortium of the research project FINE (Flexible Integration of Local Energy Communities into the Norwegian Electricity Distribution System), financed by the Research Council of Norway [project number 308833]. This work has also been supported by the BD4OPEM H2020 project, which has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 872525. Mònica Aragüés is Associate Professor and Eduard Bullich-Massagué is a lecturer of the Serra Húnter programme., Peer Reviewed, Postprint (published version)

The popular single-input single-output control structures and classic design methods (e.g., root locus analysis) for the power control of grid-forming converters have limitations in applying to different line characteristics and providing favorable performance. This paper studies the grid-forming converter power loops from the perspective of multi-input multi-output systems. First, the error dynamics associated with power control loops (error-based state-space model) are derived while taking into account the natural dynamical coupling terms of the power converter models. Thereafter, the controllability Gramian of the grid-forming converter power loops is studied. Last, a full-state feedback control design using only the local measurements is applied. By this way, the eigenvalues of the system can be arbitrarily placed in the timescale of power loops based on predefined time-domain specifications. A step-by-step construction and design procedure of the power control of grid-forming converters is also given. The analysis and proposed method are verified by experimental results and system-level simulation comparisons in Matlab/Simulink., Peer Reviewed, Postprint (published version)

Mathematical modeling of neuronal dynamics has experienced a fast growth in the last decades thanks to the biophysical formalism introduced by Hodgkin and Huxley in the 1950s. Other types of models (for instance, integrate and fire models), although less realistic, have also contributed to understand neuronal dynamics. However, there is still a vast volume of data that have not been associated with a mathematical model, mainly because data are acquired more rapidly than they can be analyzed or because it is difficult to analyze (for instance, if the number of ionic channels involved is huge). Therefore, developing new methodologies to obtain mathematical or computational models associated with data (even without previous knowledge of the source) can be helpful to make future predictions. Here, we explore the capability of a wavelet neural network to identify neuronal (single-cell) dynamics. We present an optimized computational scheme that trains the ANN with biologically plausible input currents. We obtain successful identification for data generated from four different neuron models when using all variables as inputs of the network. We also show that the empiric model obtained is able to generalize and predict the neuronal dynamics generated by variable input currents different from those used to train the artificial network. In the more realistic situation of using only the voltage and the injected current as input data to train the network, we lose predictive ability but, for low-dimensional models, the results are still satisfactory. We understand our contribution as a first step toward obtaining empiric models from experimental voltage traces., DA has been funded by the Collaboration in University Departments AGAUR Grant (COLAB 2020). AG and EF have been partially funded by the MINECO-FEDER-UE-MTM Grant RTI2018-093860-B-C21, the Generalitat de Catalunya-AGAUR projects 2021SGR01039 (AG) and 2021SGR00376 (EF), the Grants PID-2021-122954NB-I00 and PID2022-137708NB-I00 funded by MCIN/ AEI/ 10.13039/ 501100011033 and by ERDF ‘A way of making Europe’ (AG) and the Severo Ochoa and María de Maeztu Program for Centers and Units of Excellence in R &D (CEX2020-001084-M) (AG). We are grateful to the Institut d’Organització i Control (IOC-UPC) for the access to its high-performance computing facilities to perform all the computations of this work., Postprint (published version)

We consider a Thévenin equivalent circuit capturing the dynamics of a power grid as seen from the point of common coupling with a power electronic converter and propose a solution to the problem of online identification of the corresponding circuit parameters. For this purpose, we first derive a linear regression model in the conventional abc coordinates that, unfortunately, suffers from severe lack of identifiability properties. In spite of this fact, we design a bounded observer-based composite identifier that, requiring only local measurements and knowledge of the grid frequency, ensures global boundedness of the parameters estimation error and convergence to a practically small residual set. An extension that guarantees exponential convergence of these errors to zero, in the case that the grid is dominantly inductive, is further provided. The performance of the proposed identifier, which subsumes a conventional gradient descent algorithm, is illustrated via detailed computer simulations., The work of Oriol Gomis-Bellmunt was supported by the Institució Catalana de Recerca i Estudis Avançats (ICREA), Spain Academia Program. Ministerio de Ciencia e Innovación (Proyecto Equired) (PID2021-124292OB-I00)., Postprint (published version)

Este documento analiza: (1) el marco normativo de las instalaciones interiores, sus elementos y los criterios de diseño, (2) las distintas modalidades de fraude, enganches directos, enganches con contrato y puntualmente la manipulación de contadores y (3) los impactos del fraude, clasificados según su naturaleza y el actor afectado del sector eléctrico ., Preprint

Large electrical transmission networks are susceptible to undergo very large blackouts due to cascading failures, with a very large associated economical cost. In this work we propose segmenting large power grids using controllable lines, such as high-voltage direct-current lines, to reduce the risk of blackouts. The method consists in modifying the power flowing through the lines interconnecting different zones during cascading failures in order to minimize the load shed. As a result, the segmented grids have a substantially lower risk of blackouts than the original network, with reductions up to 60% in some cases. The control method is shown to be specially efficient in reducing blackouts affecting more than one zone., Peer Reviewed, Postprint (published version)

This paper discusses that the existing grid codes on the fault ride-through (FRT) opera-tion have certain complications to be implemented in the grid-forming (GFM) converters.In particular, they do not provide a clear guidelines on the suitable prioritization of thepositive- and negative-sequence currents needed for a desired voltage profile during FRToperation. To address this challenge, two FRT controls which are based on (i) voltagebalancing priority, and (ii) voltage magnitude priority are investigated for GFM convert-ers. The former gives priority to the elimination of negative-sequence voltage, while theremaining converter’s capacity is used to increase the positive-sequence voltage. On thecontrary, the latter prioritizes the increase of positive-sequence voltage, while it tries toreduce negative-sequence voltage by using the remaining converter’s capacity. The dynamicperformances of these two FRT controls are thoroughly discussed, and the simulationresults show that depending on the desired voltage profile during fault, one of them canbe implemented., Peer Reviewed, Postprint (published version)

Thisreviewprovidesthestateoftheartofenergymanagementsystems(EMS)and organizationalstructuresofprosumers.Integrationofrenewableenergysources(RES)intothe householdbringsnewchallengesinoptimaloperation,powerquality,participationintheelectricity marketandpowersystemstability.AcommonsolutiontothesechallengesistodevelopanEMSwith differentprosumerorganizationalstructures.EMSdevelopmentisamultidisciplinaryprocessthat needstoinvolveseveralaspectsofobservation.Thispaperprovidesanoverviewoftheprosumer organizationalandcontrolstructures,typesandelements,predictionmethodsofinputparameters, optimizationframeworks,optimizationmethods,objectivefunctions,constraintsandthemarket environment.Specialattentionisgiventotheoptimizationframeworkandpredictionofinput parameters,whichrepresentsroomforimprovement,thatmitigatetheimpactofuncertainties associatedwithRES-basedgeneration,consumptionandmarketpricesonoptimaloperation., Peer Reviewed, Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energia, 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, Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant, Postprint (published version)

Recent studies have developed a power electronic device known as the power router, able to fully control the power flows over the connected power lines. The present paper aims to extend the application of power routers to an electrical grid and explore its characteristics and limitations. It defines the power router grid concept, including the conditions for interconnection and architecture; it proposes a mathematical modelling methodology, analyses its operational requirements, and explores the degree of flexibility the proposed grid architecture provides. Finally, two case studies are presented to show the application of the power router grid in a practical example., 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, Hydrogen electrloyzers are power-to-gas storage devices that can facilitate large-scale integration of intermittent renewable sources into the future power systems. Due to their fast response and capability to operate in different loading conditions, they can be used as responsive loads providing support to AC grid during transients. This paper suggests taking one step further and using hydrogen electrolyzers to provide grid-forming services to the grid. As a result, the electrolyzer's role is elevated from supporting the grid (responsive load) to actively participating in forming voltage and frequency of the grid. The grid-forming capability of electrolyzer is linked to its hydrogen production constraints, which can potentially pose limitations on the grid-forming services. Besides the grid-forming mode, two additional operating modes, i.e., DC voltage mode and constant power mode, are proposed to ensure a safe operation of the electrolyzer in case of adversary interaction between grid-forming operation and hydrogen production constraints. This paper also studies the impacts of grid-forming services on the electrolyzer's physical features such as hydrogen stack temperature and efficiency. Comprehensive simulations are conducted on a low-inertia test network whose topology is inspired by a portion of the transmission grid in South Australia to confirm the effectiveness of the proposed concept under various operational conditions of the electrolyzer and upstream AC grid. Moreover, the practical feasibility of the proposed control system is experimentally validated by conducting hardware-in-the-loop tests., Peer Reviewed, Postprint (author's final draft)

Planning public electric vehicle (EV) charging infrastructure has gradually become a key factor in the electrification of mobility and decarbonization of the transport sector. In order to achieve a high level of electrification in mobility, in recent years, different studies have been presented, proposing novel practices and methodologies for the planning and operation of electric vehicles charging infrastructure. In this paper, the authors present an up-to-date analysis of the existing literature in this research field, organized by considering the perspectives and objectives of the principal actors/operators of the EV public charging infrastructure value chain. Among these actors, the electric vehicle, the charging operators and service providers, and the power system infrastructure (transmission and distribution system) are analyzed in depth. By classifying the reviewed literature based on this manifold viewpoints approach, this paper aims to facilitate researchers and technology developers in exploring the state-of-the-art methodologies for each actor’s perspective, and identify conflicting interests and synergies in charging infrastructure operation and planning., The authors would like to thank the Research Council of Norway and industry partners for the support in writing this paper under project 295133/E20FuChar—Grid and Charging Infrastructure of the Future https://prosjektbanken.forskningsradet.no/en/project/FORISS/295133?Kilde=F ORISS&distribution=Ar&chart=bar&calcType=funding&Sprak=no&sortBy=score&sortOrder=desc& resultCount=30&offset=0&Fritekst=fuchar&source=FORISS&projectId=295133 (accessed on 23 June 2023). The authors gratefully acknowledge Michele Garau, Bendik Nybakk Torsæter, and Daniel Mota from SINTEF Energy Research for their contribution to the conceptualization and review of the article. The work of Andreas Sumper was supported by the Catalan Institution for Research and Advanced Studies (ICREA) Academia Program., Postprint (published version)

The dominance of power electronics in modern power systems makes it difficult to study stability with sufficient accuracy given the available information, so it is necessary to enhance current frequency-based stability methods. The positive-mode damping (PMD) criterion is a recently powerful proposed frequency domain method to study the stability of multi-infeed VSCs grid-connected networks in the nodal admittance matrix form. The integration of black-box models and the introduction of participation factors have been identified as key lines of this work for stability studies completeness. For this purpose, a case study is built in Matlab/Simulink to address the oscillatory phenomena of modern power systems modelled in the nodal admittance matrix form with the integration of black-box models. Furthermore, this study successfully tests the performance of the participation factors applied to the PMD, which have proven to be as useful as the ones of the state-space representation in a 7-bus network example., This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 765585. This document reflects only the author’s views; the European Commission is not responsible for any use that may be made of the information it contains.This work has also been partially funded by the National Priorities Research Programn under Grant 11S-1125-170027 from the Qatar National Research Fund (a member of Qatar Foundation); FEDER/Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación, SpainProject RTI2018-095429-B-I00; and by the ICREA Academia program ., Peer Reviewed, Postprint (published version)

This short communication addresses the risk of synchronisation loss during frequency excursions for droop-based grid-forming converters when active power limitations are considered. The synchronising capability of this control approach is based on the converter’s active power exchange, which is used to generate the internal frequency of the converter control. The power available in the resource or converter ratings can impact the synchronising capability during frequency deviations. The analysis is restricted to droop-based grid-forming converters, but it could be extended to other active-power-based synchronising methods. A droop-based control is proposed to extend the operation frequency range of grid-forming converters. The performance of the suggested method is also compared to alternative ones presented in the literature. Finally, the proposed control is validated in the IEEE 9-bus system with different VSC penetration levels through EMT simulations developed in PSCAD., This work was supported by the European Union’s Horizon 2020 Research and Innovation Program (POSYTYF Project) under Grant 883985. This work was also supported by Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033) and by the European Union's Next Generation PRTR program (FAIR project), with reference TED2021-129796B-C22. Marc Cheah-Mane and Eduardo Prieto-Araujo are lecturers of the Serra Húnter programme. The work of Oriol Gomis-Bellmunt was supported by the Institució Catalana de Recerca i Estudis Avançats (ICREA) Academia Program., Peer Reviewed, Postprint (published version)

In this article we are interested in the problem of adaptive synchronization of a voltage source converter with a possibly weak grid with unknown angle and frequency, but knowledge of its parameters. To guarantee a suitable synchronization with the angle of the three-phase grid voltage we design an adaptive observer for such a signal requiring measurements only at the point of common coupling. Then we propose two alternative certainty-equivalent, adaptive phase-locked loops that ensure the angle estimation error goes to zero for almost all initial conditions. Although well-known, for the sake of completeness, we also present a PI controller with feedforward action that ensures the converter currents converge to an arbitrary desired value. Relevance of the theoretical results and their robustness to variation of the grid parameters are thoroughly discussed and validated in the challenging scenario of a converter connected to a grid with low short-circuit-ratio., Postprint (published version)

The increasing uncertainty in power systems with high penetration levels of renewable energy fosters the research on the control, management, and operation of distributed energy resources and its coupling with the current grid operation and control scheme alongside future energy markets and flexibility services. This work proposes a flexibility management system for the behind-the-meter flexibility of the distributed energy resources, which employs an adaptive auto-regression forecasting module to predict the energy cost overruns of the system throughout the energy exchanges at the point of interconnection. In addition, a cost–benefit analysis is used to evaluate and optimize the DER set-point profiles to minimize the installation’s energy cost, which, together with power redispatching and unit recommitment modules, are executed to adjust the DER operating points according to real-time deviations and short-term flexibility requests. A reference case and sensitivity analysis are performed to demonstrate the efficiency of the management system and the influence of relevant parameters. According to the results, the proposed flexibility management system reduces the total energy cost by 45% and 27.8% using quadratic and linear cost function approaches, respectively, with an average calculation time of 236 s per 900 s of execution. Dipòsits-UPCommons Corregir abstract Llistat de Treballs acadèmics Neteja CSV UPCommons Genera exportació número RACO Informe revisors UPCommons: les meves tramesses Servei de Biblioteques, Publicacions i Arxius. Universitat Politècnica de Catalunya · Barcelo, 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., This paper proposes a new decentralized strategy for optimal grid frequency regulation (GFR) in an interconnected power system, where onshore grids and offshore wind farms (OWFs) are linked using a multi-terminal high-voltage direct-current (MTDC) system. In the proposed strategy, grid- and OWF-side optimal controllers are developed to coordinate the operations of synchronous generators and the MTDC converter, and the OWF and the MTDC converter, respectively, thus achieving optimal generator power and deloaded OWF power sharing of the interconnected grids and minimizing frequency deviations in each grid. Full-order dynamic models of an MTDC-linked grid and an OWF are implemented, and given each dynamic model, grid- and OWF-side decentralized linear quadratic Gaussian regulators are designed for optimal GFR of the MTDC-linked grids and supporting GFR through optimal deloading operation of the OWFs, respectively. Eigenvalue analyses are conducted with a focus on the effects of system parameter uncertainties and communication time delays. Comparative case studies are also performed to verify that the proposed strategy improves the effectiveness and stability of real-time GFR in MTDC-linked grids under various conditions., Postprint (author's final draft)

This paper presents a short-circuit analysis of grid-connected photovoltaic (PV) power plants, which contain several Voltage Source Converters (VSCs) that regulate and convert the power from DC to AC networks. A different methodology has been adopted in this paper for short-circuit calculation. In particular, an element-based formulation is adopted to model the studied system including the grid-support control and various current-saturation states of PV inverters during the fault. An iterative approach is presented to identify the short-circuit equilibrium point that satisfies all converters’ operation limits efficiently. Case studies have been carried out on PV power plants with different numbers of inverters. The influence of the inverter grid-support operation, the main grid strength and the MV collection grid topology on system steady-state performance during the fault has been analyzed. The obtained short-circuit equilibrium points have been validated through dynamic simulations., Peer Reviewed, Postprint (author's final draft)

Phasor models have been widely used in short-circuit simulations, in which system operators verify the behaviour of the grid over thousands of different contingencies. However, it is still unclear if phasor models can still be used in fault studies in modern or future power grids dominated by renewable generation with power electronics and converters. Therefore, this paper analyses the suitability of phasor models to simulate short-circuit transients in grids with grid-following (GFL) and grid-forming (GFM) voltage-source converters (VSC). Phasor models of GFL and GFM were developed and tested in two test systems, one with 50% of converters in the generation mix and another powered 100% by converters. Asymmetrical and symmetrical faults were applied at different points of the systems and key variables were used to compare the phasor models against EMT models during the transients. The results showed that, despite neglecting transients in the grid, phasor models could be used in a preliminary stage of short-circuit studies as it was capable of tracking the steady-state value of almost all variables analysed. In this case, detailed EMT simulations, although necessary, would be used only at more advanced stages of the studies., Peer Reviewed, Postprint (author's final draft)

© 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 Thévenin equivalent is considered as the standard grid equivalent for power system analysis. The integration on power electronics components in the power systems introduces non-linear operation characteristics that cannot be captured by Thévenin equivalent. Therefore, an alternative grid equivalent representation is required. This paper presents a steady-state equivalent representation of power systems with penetration of power electronics, which is suitable for both normal operation studies and short-circuit calculations. This equivalent grid representation is developed based on the voltage-current (U-I) characteristic of a power system to map the relationship between voltages and currents of a specific network node. Such grid equivalent representation has been presented for single-phase, balanced and unbalanced three-phase power systems in this paper. A methodology is presented to identify operation points when the equivalent system under study is connected to any external system. The proposed equivalent grid representation and the methodology for operation points identification have been tested on the Voltage Source Converter (VSC) based test system and are validated through dynamic simulations., This work was supported by FEDER / Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación, Spain, through projects PID2021- 124292OB-I00 and PID2019-103849GB-I00 as well as Generalitat de Catalunya through project 2021-SGR-00603. Marc Cheah-Mane is also a Serra Húnter Lecturer. Eduardo Prieto-Araujo is also a Serra Húnter Associate Professor. Oriol Gomis-Bellmunt is also an ICREA Academia researcher., Postprint (author's final draft)

This article proposes an intuitive methodology to analyse and mitigate system-level interactions in hybrid ac/dc networks interconnecting ac grids of arbitrary strengths, and especially weak grids. In particular, the challenge of interconnecting such grids is posed as an interaction problem in which the mechanism can be analysed explicitly through the unique ac/dc interaction functions. Then, it is demonstrated how these interaction functions can be manipulated to mitigate ac–ac, ac–dc, and dc–dc interactions simultaneously through a simple augmentation of the classic vector current control structure. The augmented loop adopts supplementary bus-voltage feedforwards from the ac and dc-sides. Significant improvements over the classic structure are demonstrated for an high voltage dc-link connecting two ac grids with arbitrary grid strengths particularly a very weak ac connection. It is shown how these supplementary loops provide a more inclusive and flexible solution to contradictory requirements on existing control, with a thorough system outlook. In addition, it is shown that the augmented loop is also beneficial for system dynamics when the grid is strong than without it. The analysis is carried out in the frequency domain, and performance is validated with nonlinear time-domain simulations., Postprint (author's final draft)

This short-communication presents a steady-state analysis of a grid-forming Modular Multilevel Converter (MMC) providing optimal voltage support to the AC network under normal and constrained conditions. The analysis is performed based on a multi-objective function (OF) optimization problem which prioritizes to maximize the positive-sequence and to minimize the negative- and zero-sequence voltage components at the point of common coupling (PCC) while it also considers the minimization of the arm impedance losses, respectively. If the voltage condition at the PCC is satisfied, the optimization attempts to reduce the arm impedance losses; otherwise, the algorithm prioritizes the PCC’s voltage components in order to minimize the error. Different network voltage and internal fault scenarios are evaluated, where it is shown that the suggested problem formulation can be used to obtain the optimal MMC’s quantities, providing voltage support during the faults., This work was supported by the Ministerio de Ciencia e Innovación (Proyecto Equired) under Grant PID2021-124292OB-I00. This work was also supported by the Agencia Estatal De Investigación, Spain under Grant PID2021-127788OA-I00. Eduardo Prieto-Araujo is an associate professor of the Serra Húnter programme. The work of Oriol Gomis-Bellmunt was also supported by the Institució Catalana de Recerca i Estudis Avançats (ICREA), Spain Academia Program., Peer Reviewed, Postprint (published version)

Nowadays, offshore renewable energy is seen more and more as an attractive alternative to onshore energy thanks to less space limitations and usually better weather conditions. However, the higher costs in installation and maintenance demand a continuous search for higher conversion efficiency in order to achieve an economically viable electricity generation. In this line, the co-location of wind and wave power sources might serve to reduce the generation power variability and also to take advantage of using the same infrastructure and implementation area. Several studies have been carried out mainly focused on determining possible zones of implantation or developing new co-location concepts. However, the optimization and control of these new offshore energy conversion systems have not been extensively studied in the literature. This article presents a new optimal control strategy for co-located wind and wave farms in order to fulfill the operation and integration requirements demanded by power system operators. The proposed control scheme is evaluated in several realistic scenarios. The obtained results show that with adequate control strategies, it is possible to increase the electricity production of co-located wind-wave farms satisfying the frequency requirements of the network, even in adverse events, and also to increase the total power reserve of the system., Peer Reviewed, Postprint (published version)

This paper presents a live field experience of creating an isolated microgrid for the Expoelectric fair during 2018 and 2019. The islanded microgrid comprises a Master Inverter with grid-forming capabilities and fault management. The Master Inverter and stationary batteries, and EVs with V2G capabilities provide storage. A PV generation system supplies the microgrid. The loads are the fair booths, mainly lighting and chargers for personal mobility vehicles. All the equipment used in the experimental microgrid is from different manufacturers. The operation and control of the islanded microgrid are based on the VDE-AR-N-4105 standard. The paper also presents the operation of the Master Inverter during faults. The live field experience shows that the proposed operation method is valid for operating different converters from different manufacturers without needing any communication layer between them. The experimental results also show that faults can be handled correctly by the Master Inverter to operate the entire microgrid safely. In conclusion, islanded microgrids based on power electronics are feasible to replace diesel generators in faires, conventions or temporary events., Peer Reviewed, Postprint (published version)

The impedance-based analysis has been extensively used for frequency domain stability analysis in power systems with power electronics devices. Also, such analysis is used to determine the oscillatory mode frequencies. The impedance ratio analysis is a conventional approach employed to determine both stability conditions and oscillatory mode frequencies. In particular, oscillatory mode frequencies can be approximated from the gain and phase crossover of the impedance ratio. Such an assumption has been considered in the harmonic frequency range, but in the low frequency range, approximately under 100 Hz, this might not be valid. Low frequency interactions are mainly caused by voltage source converter outer loops and synchronous generator circuits and controls. This paper presents an alternative impedance-based analysis to identify mode frequencies and the participation of impedance components to the interactions. This method is compared to the approximation from the gain and phase crossover of the impedance ratio. Also, the simplification of synchronous generators as Thévenin equivalents is explored for low frequencies based on the impedance frequency response. An essential power system model with a voltage source converter, a synchronous generator, and a load is presented to show the advantages of this alternative impedance-based analysis compared to the gain and phase crossover of the impedance, Peer Reviewed, Postprint (published version)

A fully normalized algorithm to implement the optimal triple-phase-shift (TPS) modulation strategy of the dual active bridge (DAB) converter is proposed in this article. The algorithm evaluates three simple expressions that fit the optimal solutions obtained in recent works, which allows the algorithm to be implemented in real-time and valid for the whole operating range. As a result, the converter operates under zero voltage switching (ZVS) conditions and minimizes conduction losses. In addition, the algorithm considers the minimum current required to guarantee the ZVS condition that faces the undesired dead-band of switching devices effect. The proposal achieves a soft transition between any operation region and a fast closedloop response with no stability concern, presenting robustness under leakage inductance deviation. Finally, the algorithm presented in this article is verified with a 4-kW experimental prototype. Experimental results show that the algorithm proposed can be evaluated with less than 2.8 µs and allows soft transition between any operation region to be achieved. Besides, fast closedloop changes of 750 µs through all the operating ranges, keeping minimum rms current under ZVS, are shown, Peer Reviewed, Postprint (published version)

This article is written within the European Project “THREE-Lanka” which has the aim of modernizing the higher education related to Renewable Energy (RE) in Sri Lanka. The paper presents the outcomes of analysing various incentive schemes to stimulate RE development. In Europe, there was substantial growth in RE installation through generous incentives in the first years. Then, to regulate this growth, in recent years, the auction system has been introduced to improve the competition among companies that install RE plants. In Sri Lanka, on the other hand, the main energy tariff policies focus on the spread of PhotoVoltaics (PV) through contributions based on the electricity fed into the grid. This paper provides an updated view of the evolution of the energy tariff policies in the relevant European countries with respect to Sri Lanka, covering some recent policy developments. Within the Sri Lankan framework, four case studies involving residential, commercial, and industrial users are outlined to suggest better mechanisms (in the case of not adequate current incentive tariff) for supporting the deployment of grid-connected PV systems in a wide power range. Such knowledge transfer in the THREE-Lanka project will demonstrate the enormous potential RE capacity in a developing country, still depending on fossil fuels but willing to follow the path towards sustainability., Peer Reviewed, Postprint (published version)

This article reviews Flux-Weakening (FW) algorithms for Permanent Magnet Synchronous Machines (PMSMs), focusing on the automotive sector, especially in electric and hybrid electric vehicles. In the past few years, the spread of Electric Vehicles (EVs) has improved the technology of electric machines and their control to achieve more compact and competitive solutions. PMSMs are the most widespread electric machines used in EVs thanks to their high-power density and potential operation at constant power range during high speed. Such high speed implies a high electromotive force. An FW technique is mandatory to reduce the electromagnetic flux generated by the electric machine due to the voltage limits of the traction inverter and the energy source. This article classifies and analyses the state-of-the-art FW control strategies by comparing their main advantages and drawbacks. The Vector Current Control (VCC) method that regulates the modulus of the applied voltage is the most common one in the literature thanks to i) its robustness to parameter modification and model unsureness, ii) low computational complexity, and iii) high dynamic response and control stability., Peer Reviewed, Postprint (published version)

Recent environmental policies have led academic, industrial, and governmental stakeholders to plan scenarios with a high share of renewable energy sources (RES), to ensure that future energy systems, composed mostly of RES, can remain stable, match the demand during seasonal variations and are economically feasible. This article considers different energy scenarios to obtain various options in terms of size, generation technologies, and grid configuration. The scenarios are studied in the POSYTYF project and are quantified through an optimization-based algorithm, where the test grids topologies are based on specific locations in Europe, and real data related to the availability of RES, as well as the demand. Different RES technologies are considered to meet requirements of grid integration of renewables at different horizons of time, up to 100% in the most futuristic case. The optimization algorithm is applied to three scenarios. It is shown that solar photovoltaic (PV) and wind can provide the renewable backbone, but they lack flexibility to achieve a very high share in the energy mix. Solar thermal and pumped hydro become important to cover the last range of integration, as they provide high flexibility, which is crucial for high share, but they are expensive for low share., Peer Reviewed, Postprint (published version)

In this work, a battery consisting of eight commercial NMC/graphite cells connected in series was cycled to 60% of its initial capacity. During the test, special care was taken to ensure that the results were not influenced by either the module assembly or the module design. For this purpose, the cells were virtually connected in a laboratory environment with the help of the test device as if they were operated together in a battery. Extrinsic influences that affect cell aging were thus reduced to a minimum. Differential Voltage Analysis (DVA), Electrochemical Impedance Spectrum (EIS), and relaxation measurements were performed to analyze the aging behavior of each cell. The results show that despite a theoretically perfect module design, Cell-to-Cell Variations (CtCV) occurred during aging. The shifting Depth of Discharge (DoD) values among the cells further amplify CtCV. Lithium plating was also observed in the faster aging cells after cyclic aging, suggesting that this aging effect contributes significantly to the development of CtCV. After the aging test, the battery was equipped with an active balancing system that maximizes capacity utilization. More important, the balancing charges which are calculated iteratively within the used balancing algorithm show a strong correlation to the pure capacity losses and thus provide a new way to determine the capacity values of each cell individually without disassembling the battery., Peer Reviewed, Postprint (published version)

This paper introduces semi-explicit multilinear modeling to ac power systems, including voltage source converters. Firstly, the novel semi-explicit multilinear modeling class is explained. Then this class is applied to a small example of PV inverter connected to an infinite bus. Some part of the nonlinear current reference calculation is expressed as a multilinear algebraic constraint. The formulation of this multilinear algebraic constraint allowed modeling the whole nonlinear inverter as a semi-explicit multilinear model. The novel modeling approach is compared with common nonlinear time-based simulation in Simulink. The results show a good approximation of the nonlinear model by its semi-explicit multilinear model where the relative error is below . This low error motivates the further usage of the semi-explicit multilinear modeling class for power system analysis., 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, This paper proposes an optimization-based size reduction methodology for Modular Multilevel Converters (MMC), focusing on minimizing the converter's sub-module capacitor CSM. The analysis is performed considering both the converter's current and voltage limitations and the Transmission System Operator (TSO) Fault Ride Through (FRT) requirements. By means of a steady-state analysis, the time-domain expressions of the converter's arms energies are obtained and their behavior throughout the MMC's operating range is shown. Based on these expressions, the optimization-based problem to reduce the CSM size is developed and its constraints are imposed to ensure that the converter's voltage and current levels are within its design limitations. The suggested method is compared with different approaches for distinct active and reactive power set-points, where it is shown that the SM capacitor size can be reduced up to 24% in comparison with the method with worst performance and up to 7% regarding the best method used for comparison purposes. Furthermore, time-domain simulations of the MMC considering several AC voltage sags are performed in order to demonstrate that the dynamics of the SM capacitor and the arm applied voltages are within acceptable margins during the different operations., Postprint (author's final draft)

The result of J.C. Willems et al. “A note on persistency of excitation”, System & Control Letters, 2005 gives identifiability conditions for system identification as well as data-driven representations for data-driven control. The existing proofs however are proofs by contradiction and do not give insight into the assumptions of controllability and persistency of excitation of the input. Moreover, the existing proofs do not clarify how conservative the assumptions are. We provide an alternative constructive proof for the single-input case. It is shown that persistency of excitation of order more than the time horizon is needed in nongeneric cases, corresponding to special initial conditions. The special initial conditions are explicitly characterized in terms of the solution of a Sylvester equation. Another contribution of the paper is a representation of a scalar persistently exciting input of a finite order as an output of an autonomous linear time-invariant system, Peer Reviewed, Postprint (published version)

Fraud detection in distribution grids is an important issue that can significantly impact the efficiency and profitability of the grid. This paper presents a hybrid fraud detection system using both Smart Meter and grid data. The methodology uses clustering and correlation tools, such as the Matthews Correlation Coefficient, to flag potential fraudsters based on strategies defined by the Distribution System Operator. The algorithm has been tested on several synthetic grids and resulted effective in detecting fraudulent activity. This tool has been developed within the BD4OPEM H2020 project., This work has been supported by BD4OPEM H2020 project (2020-2023) and received funding from the European Union’s Horizon 2020, under grant agreement No 872525. The research of Marc Jené-Vinuesa has received support from the Generalitat de Catalunya under the FI-AGAUR Pre-doctoral grants and scholarships (FI-2020). Mònica Aragüés-Peñalba is Lecturer at UPC of the Serra Húnter Programme. We would like to thank to Ramon Gallart Fernandez and its innovation team at Estabanell y Pahisa Energia S.A. (EyPESA) for providing data and insights for this work., 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., In emerging Multi-Terminal High Voltage Direct Current (MT-HVDC) systems interconnecting different Alternating Current (AC) asynchronous areas by means of Interconnecting Power Converters (IPC) different challenges arise. One of them is the control role assignment of IPCs present in these systems. Broadly speaking, the IPC controls can be classified into grid-forming or grid-following schemes for both AC and DC terminals of IPCs. This paper presents a methodology to optimize the control role assignment of the IPCs considering i) small-signal stability and, ii) control performance for different combinations of IPC roles and network power flows. The method considers multiple power flows, determines the steady-state deviations, and small-signal stability following selected events. While presenting this methodology different results on the small-signal and steady-state analysis of these systems are analyzed. Using high-fidelity linearized dynamical models, an optimization problem is formulated to assign control modes to IPCs to ensure stability and performance of the system for a set of given power flow scenarios., Postprint (published version)

The stability, operation, and control of power networks have been challenged due to the increased penetration of power electronic converters. New instability phenomena have appeared due to the interaction of the power converter controllers with other power network elements, including other power converters. Small-signal tools have been proved effective to identify and mitigate stability issues but their development is still ongoing. This article presents the state of the art on small-signal modeling and stability assessment of converterdominated networks. The modeling of converters and other power system components is reviewed, as well as the most common small-signal analysis techniques employed in conventional and modern power systems with power electronics. Two case studies are introduced to exemplify the modeling and stability analysis, employing some of the techniques presented in the article., Peer Reviewed, Postprint (published version)

© 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, This paper proposes a comprehensive analysis of the Modular Multilevel Converter (MMC) focusing on the different arm applied voltage components, that this paper will refer as degrees of freedom (DOFs), which must be considered in order to perform the internal energy balancing of the converter. The analysis relies on the commonly used differential and additive reference frames. By means of a steady-state analysis, the different voltages components applied and currents components flowing through the converter are studied and an in-depth discussion of the roles of each DOF in the converter is presented. Furthermore, the mathematical expressions of the power exchanged between the AC/DC networks and within the converter, between the arms (vertical) and among phase-legs (horizontal), are derived considering all the DOFs of the MMC, revealing potential interactions among the differential and additive quantities. Finally, the theoretical analysis is validated through comparisons between the values obtained with the mathematical expressions and the simulation results assuming different case scenarios., Peer Reviewed, Postprint (author's final draft)

Microgrids are generally low-inertia systems with a high penetration of renewable energy sources. The design of advanced control structures is required to keep these grids’ electrical variables within an acceptable range. In this context, the present article proposes an intelligent secondary controller for islanded microgrids using the Deep Deterministic Policy Gradient (DDPG). The DDPG controller changes the output power of the storage elements to secure the voltage and frequency stability. This work tested the designed controller for a microgrid that comprises a synchronous generator, two battery energy storage systems and one photovoltaic generator. The controller performance was compared to droop controllers, considering a short-circuit event, feeder and load disconnections. Results showed a consistent reduction of the microgrid’s voltage and frequency deviations with the DDPG algorithm., Peer Reviewed, Postprint (author's final draft)

In an MMC station, the submodule (SM) capacitor constitutes a high proportion in both the footprint size and construction cost, which greatly limits the application of MMC in some scenarios, such as offshore wind power transmission system. Since the SM capacitor voltage ripple has a close interaction with the phase circulating current in MMC, an appropriate management of circulating current is widely acknowledged to reduce the SM capacitance. This paper proposes a novel design of circulating current control target to minimize the requirement of SM capacitance in MMC. Firstly, the phase angle of circulating current is designed to significantly reduce the fundamental and second-harmonic capacitor voltage ripple at the same time. Secondly, the magnitude of circulating current is determined to achieve the optimal phase angle or magnitude coordination between the components of SM capacitor voltage ripple. Thus, under the proposed design method, the peak-peak capacitor voltage ripple is minimized and the requirement of SM capacitance can be effectively reduced. Finally, an MMC-HVDC case system connecting to the offshore wind farm is built on PSCAD/EMTDC to validate the effectiveness of the proposed design method., Peer Reviewed, Postprint (author's final draft)

The term “Moonshot Thinking” has become popular in the last few years and represents pursuing objectives that appear undoable, but it could redefine humanity if implemented. It should tackle enormous societal challenges in the long term and shape desired futures in the process. The urgency of climate change, the upcoming challenges, and the required outcomes make the energy domain an ideal field for applying this methodology. Therefore, the InnoEnergy MSc Energy for Smart Cities Moonshot pilot subject was implemented in the Master's program during the second year at the UPC in Barcelona. This project-based course aims to provide the students with skills in new project management methodologies, futures thinking, innovation, problem-solving, and rapid prototyping while addressing a huge problem in the field of energy and sustainable cities. The paper describes the design of this challenge-based course, discussing the experience of the two years of piloting implemented at the UPC, including the feedback from the students, Peer Reviewed, Postprint (published version)

This paper deals with the short-circuit calculation of offshore wind power plants (OWPPs). The short-circuit calculation presented in this paper assumes the studied system achieves a new equilibrium state during the fault. The studied system is modeled with an element-based steady-state formulation where the grid-support control and potential current-saturated operation of wind turbine (WT) converters are included. In particular, the current-saturation modifies the converter control and represents various potential operation states of the converter. Then, an iterative methodology is proposed to identify the short-circuit equilibrium point that satisfies converters’ limitations and to obtain the current-saturation states of all power converters with a specific fault scenario in the studied system. The numerical case studies indicate that the WT converters operation has a significant influence to the system equilibrium point during the fault. In addition, the presented methodology is efficient for short-circuit calculation of a large-scale OWPP., Peer Reviewed, Postprint (published version)

© 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, This article presents an accurate method to determine the mandatory rotor position to control a permanent magnet synchronous machine from misplaced Hall-effect switch sensors. The main feature of this technique is the estimated speed from two consecutive edge transitions in the same phase to dodge the inaccurate information. Besides, when a new electrical cycle starts, a gradual compensation algorithm corrects the initial speed estimation to cancel the electrical angle error in order to prevent current distortions. Furthermore, a first-order Taylor series approximation estimates the rotor position from the compensated speed calculation, reducing the possible torque ripple and noise due to an inaccurate control strategy. The proposed method has been compared with other state-of-the-art approaches through simulation and experimental results obtained from a low-voltage powertrain, showing more straightforward implementation and delivering the best balance performance during steady-state and transient operation., Peer Reviewed, Postprint (author's final draft)

In this paper, a generalized average model for various topologies of series interline power flow controller is developed and incorporated in AC/DC VSC MTDC power flow model. A new Newton Raphson based power flow formulation of AC/DC VSC MTDC system with series interline power flow controller in proposed. The proposed formulation accommodates the inclusion of capacitor voltage limits of Current Flow Controller (CFC), DC line current and duty cycle limits. Steady State feasibility of wind power evacuation is analyzed for different wind power penetration levels and CFC injected voltages. The impact of CFC injected voltages on rerouting and nullifying the power flows in MTDC grid are analyzed for different wind power penetration levels. Initialization of state variables for feasible steady state solution has been addressed. In order to ensure feasible solution a novel convergence criteria is proposed. The validity of the proposed AC/DC power flow formulation is demonstrated on 39 bus AC/DC system., Peer Reviewed, Postprint (published version)

Modern power systems are facing the tremendous challenge of integrating vast amounts of variable (non-dispatchable) renewable generation capacity, such as solar photovoltaic or wind power. In this context, the required power system flexibility needs to be allocated in other units that can include energy storage, demand management or providing reserve from renewables curtailing the output power. The present paper proposes the new concept of grid-forming load, which can be considered a totally flexible concept of demand. The concept is not only ensuring the load is supporting the grid stability by adapting the load to the overall system balancing, but also ensures that the load is actually contributing to form the grid and to provide synchronization power to the overall system. In this sense, the new concept allows running a system powered only by renewables operating at maximum power (or operator defined set-point) in grid-following mode, while the overall system control is ubicated in the demand side. This is an important change of paradigm as it considers that all the flexibility, synchronism and stability provision is on the demand side. This concept can applied either to isolated systems or also to future power systems, where millions of loads steer the power system while the renewables are operating at full power. The paper proposes the concept, suggests possible control implementations of the grid-forming load and analyses the concept in four simulation case studies., Peer Reviewed, Postprint (published version)

High-voltage direct current (HVDC) transmission system based on modular multilevel converter (MMC) technology is considered as an attractive solution for the interconnection of two AC grids to enhance the security of supply. Several studies have concluded that the AC grid impedance is a key parameter for the control system design of the MMC. Such important design parameter, however, is subject to wide variations due to the time-varying nature of AC grid and the future modifications and expansions. Therefore, the grid impedance has to be considered as an uncertain parameter during control design stage. To this end, this paper suggests a robust multivariable controller which is able to maintain system stability and performance for an extended range of grid impedance uncertainties. To ensure that the controller operates robustly in a wide range of grid impedances, structured singular value of the system (known as ) is minimized via an iterative procedure. In such procedure, the uncertainties are separated from the nominal linear model of the system and the weighing functions are tuned to fulfill the robustness criteria defined by the small-gain theorem. The effectiveness of the suggested controller and the design procedure is validated by means of simulation results., Postprint (author's final draft)

© 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, This paper proposes a new strategy for optimal grid frequency regulation (FR) in an interconnected power system where regional ac grids and an offshore wind farm are linked via a multi-terminal high voltage direct-current (MTDC) network. In the proposed strategy, decentralized H8 controllers are developed to coordinate the operations of synchronous generators and MTDC converters, thus achieving optimal power sharing of interconnected ac grids and minimizing frequency deviations in each grid. To develop the controllers, robust optimization problems are formulated and solved using a dynamic model of the hybrid MTDC-linked grids with model parameter uncertainty and decentralized control inputs and outputs. The model orders of the controllers are then reduced using a balanced truncation algorithm to eliminate unobservable and uncontrollable state variables while preserving their dominant response characteristics. Sensitivity and eigenvalue analyses are conducted focusing on the effects of grid measurements, parameter uncertainty levels, and communication time delays. Comparative case studies are also carried out to verify that the proposed strategy improves the effectiveness, stability, and robustness of real-time FR in MTDC-linked grids under various conditions., This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (corresponding author: Y. Kim)., Postprint (author's final draft)

In this paper, we present a novel control approach for dynamic virtual power plants (DVPPs). In particular, we consider a group of heterogeneous distributed energy resources (DERs) which collectively provide desired dynamic ancillary services such as fast frequency and voltage control. Our control approach relies on an adaptive divide-and-conquer strategy: first, we disaggregate the desired frequency and voltage control specifications of the aggregate DVPP via adaptive dynamic participation matrices (ADPMs) to obtain the desired local behavior for each device. Second, we design local linear parameter-varying (LPV) H8 controllers to optimally match this local behaviors. In the process, the control design also incorporates the physical and engineered limits of each DVPP device. Furthermore, our adaptive control design can properly respond to fluctuating device capacities, and thus include weather-driven DERs into the DVPP setup. Finally, we demonstrate the effectiveness of our control strategy in a case study based on the IEEE nine-bus system., Peer Reviewed, Postprint (published version)

Modular multilevel converters (MMCs) have emerged as a viable choice in future DC grid architectures due to their scalability to meet voltage level requirements. However, MMC-based DC distribution systems are at risk of short-term outages during the faults in either the DC or AC networks feeding the MMC, so it remains a challenge to accomplish AC and DC fault ride-through (FRT) capability in such applications. To ensure stable operations of the DC terminals, FRT strategies are required for the faults on both the AC and DC sides of the converter. This paper proposes a FRT strategy for the AC and DC side of the converter to ensure stable and economically viable operation of the DC distribution network. The asymmetrical faults in the upstream AC grids are managed by using the integrated energy of the MMC. Whereas, the DC FRT capability of the MMC is accomplished by changing the redundant submodules of the MMC to full-bridge submodules (FBSMs), thus allowing a DC FRT to be achieved by using DC circuit breakers that are low cost and reduced in size. Applying the proposed DC FRT strategy, which makes possible the use of low-cost and reduced in size DC circuit breakers in DC distribution, results in a reduction in the overall initial investments., Peer Reviewed, Postprint (published version)

Flexibility has emerged as an optimal solution to the increasing uncertainty in power systems produced by the continuous development and penetration of distributed generation based on renewable energy. Many studies have shown the benefits for system operators and stakeholders of diverse ancillary services derived from demand-side flexibility. Cost-benefit analysis on these flexibility services should be carried out to determine the profitable applications, as well as the required adjustments on energy market, price schemes and normative framework to maximize the positive impacts of the available flexibility. This paper endeavors to review the main topics, variables and indexes related to the profitability analysis on demand-side flexibility, as well as the influence of energy markets, pricing and standards on revenue maximization. The conclusions drawn from this review demonstrate that the profitability of flexibility services considerably de-pends on energy market structure, involved assets, electricity prices and current ancillary services remuneration., Peer Reviewed, Postprint (published version)