European White Book on Real-Time Power Hardware in the Loop Testing : DERlab Report No. R- 005.0

The European White Book on Real-Time-Powerhardware-in-the-Loop testing is intended to serve as a reference document on the future of testing of electrical power equipment, with specifi c focus on the emerging hardware-in-the-loop activities and application thereof within testing facilities and procedures. It will provide an outlook of how this powerful tool can be utilised to support the development, testing and validation of specifi cally DER equipment. It aims to report on international experience gained thus far and provides case studies on developments and specifi c technical issues, such as the hardware/software interface. This white book compliments the already existing series of DERlab European white books, covering topics such as grid-inverters and grid-connected storag

A review of design criteria for low voltage DC distribution stability

The performance advantages for Low Voltage Direct Current electrical distribution is becoming clearer however, the commercial opportunities, design processes and standardisation is currently lacking. This paper presents an overview of the current development status of LVDC distribution and reviews the modelling and stability criteria available to designers of DC distribution systems for land, aerospace and marine power system applications

Control and stability of Ac/Dc microgrids

The current society is facing several challenges related to the field of energy, such as the high dependency on fossil fuels, the constant increment in the energy consumption and the environmental problems caused by these factors. The integration of distributed generation systems—mainly based on renewable energies—combined with energy storage systems is the most interesting solution to tackle these issues. However, most of these systems are connected to the grid through electronic converters that actively control the power exchange. This fact causes various problems not suffered since the origins of electric grids in the transition from an electric model dominated by synchronous machines to a model where power electronics gain more importance—even being the dominating systems in some cases. The lack of inertial response and primary reserve, the instabilities caused by the interactions of power electronic systems or the premature situation of direct current grids, which are being employed more widely, stand out as some of the most important challenges that we want to address with this thesis. In this context, the main purpose of the thesis is the development of ac/dc microgrid control strategies that improve the dynamic behaviour of the system. In order to achieve this objective we contemplate four main lines that consist of the identification and analysis of different microgrid topologies and control techniques, the study of primary control operation modes of the systems that compose these microgrids and finally the the development and evaluation of various low-level control strategies for ac and dc microgrids. These techniques are based on the concept of operation of classical synchronous generators, enabling their autonomous operation as well as providing inertial response under grid perturbations. Among the contributions of the thesis, we can highlight on the one hand, the analysis and comparative evaluation of synchronous machine emulation techniques for ac microgrids, where we evaluate their behaviour for different types of perturbations and we examine their stability applying the generalized Nyquist criterion. Regarding dc microgrids, on the other hand, we propose novel control techniques that are analogous to the ones analysed for ac grids. We call these techniques virtual-capacitors, as they emulate the behaviour of these passive elements connected to dc grids. In this case, we thoroughly study their transient as well as steady-state behaviour, and we demonstrate that they can be adapted by simply modifying control parameters. Moreover, we analyse the stability of these techniques through parametric analysis of their dominant eigenvalues.Gaur egungo gizartea energiaren arloko hainbat erronkaren aurrean aurkitzen da, besteak beste, erregai fosilekiko dependentzia handia, kontsumo energetikoaren etengabeko igoera, eta faktore hauek eragiten dituzten ingurumen arazoak. Generazio bananduko sistemen integrazioa—bereziki iturri berriztagarrietan oinarritutakoa—metatze sistemekin bateratuta, arazo horiei aurre egiteko aukera interesgarriena bilakatu da. Hala ere, sistema hauetako gehienak bihurgailu elektronikoen bitartez konektatzen dira sare elektrikotara, potentziaren hartu-emana modu aktiboan kontrolatzen dutelarik. Honek, makina sinkronoez menderatutako modelo elektriko batetik, potentzia elektronika garrantzia hartzen hasten den—edo kasu batzuetan mendean dagoen—modelo baterako trantsizioan hainbat arazo eragiten ditu, sare elektrikoak sortu zirenetik jasan ez direnak. Erantzun inertzial eta erreserba primario eza, bihurgailuen interakzioaren ondoriozko estabilitate arazoak edo korronte zuzeneko sareen egoera goiztiarra, geroz eta gehiago erabiltzen direnak, tesi honen bitartez aurre egin nahi diren erronkarik garrantzitsuenetarikoak dira. Testuinguru honetan, tesiaren helburu nagusia ac/dc mikrosareen portaera dinamikoa hobetzen duten kontrol estrategiak garatzea da. Helburu hau lortzeko lau lerro nagusi planteatu dira, besteak beste, mikrosareen topologia eta kontrol estrategia desberdinen identifikazio eta analisia, sare hauek konposatzen duten sistemen kontrol primarioaren untzionamendu motak azterketa, eta azkenik, bai ac eta bai dc mikrosareendako nibel baxuko kontrol estrategia desberdinen garapena. Azken hauek generadore sinkrono klasikoetan oinarritu dira, modu autonomoan eta bananduan aritzeko gaitasuna emateaz gain, sareko perturbazioen aurrean erantzun inertziala ematea ahalbidetzen dielako. Tesiaren ekarpenen artean, alde batetik, makina sinkronoen emulazioan datzan kontrol estrategien analisia eta konparaketa azpimarratu behar dira. Kasu honetan, teknika hauek hainbat perturbazioetarako ebaluatzen ditugu, eta Nyquisten kriterio generalizatuan oinarrituta estabilitatea aztertzen dugu. Korronte zuzeneko sareei erreparatuz, bestalde, kontrol teknika berriak proposatzen ditugu. Hauei kondentsadore-birtual izena ezarri diegu, elementu pasibo horien erantzun dinamikoa emulatzen dutelako. Hemen, teknika hauen erregimen iraunkorreko eta iragankorreko erantzuna aztertzen dugu, soilik kontrol parametro batzuk aldatuta egokitu daitezkela frogatuz. Hortaz gain, sistema hauen estabilitatea aztertzen dugu berezko balio dominanteen (eigenvalue-en) analisi parametrikoak eginez.La sociedad actual se enfrenta a varios retos importantes en materia energética, entre los que destacan la gran dependencia de los combustibles fósiles, el constante aumento del consumo energético y los problemas medioambientales que estos factores conllevan. La integración de sistemas de generación distribuida—principalmente de origen renovable— combinadas con sistemas de almacenamiento de energía, se presenta como la solución más interesante para hacer frente a estos retos. Sin embargo, la mayor parte de estos sistemas se conectan a la red a través de convertidores electrónicos que controlan el intercambio de potencia de manera activa. Este hecho hace que la transición desde un modelo eléctrico principalmente dominado por máquinas síncronas, hacia un modelo donde la electrónica de potencia comienza a cobrar protagonismo—hasta el punto de llegar a ser dominante en algunos casos—acarree diversos problemas que prácticamente no se han manifestado desde los orígenes de las redes eléctricas. La falta de respuesta inercial y reserva primaria, las inestabilidades debidas a la interacción de los sistemas electrónicos de potencia o la prematura situación de las redes de corriente continua, cada día utilizadas en mayor medida, destacan como algunos de los retos más importantes a los que se quiere dar respuesta a través de esta tesis. En este contexto, el objetivo principal de la tesis es el desarrollo de estrategias de control de microrredes ac/dc que mejoren el comportamiento dinámico del sistema. Para la consecución de este objetivo se han planteado cuatro líneas principales que constan de la identificación y análisis de diferentes topologías y técnicas de control de microrredes, el estudio de los modos de operación del control primario de los sistemas que las componen, y finalmente, el desarrollo y evaluación de diversas técnicas de control de nivel bajo tanto para microrredes ac como dc. Las estrategias de control de nivel bajo desarrolladas en la tesis se basan en el concepto de operación de los generadores síncronos clásicos, lo que les permite operar de manera distribuida y autónoma, aportando a su vez respuesta inercial ante perturbaciones en la red. Entre las contribuciones de la tesis destacan, por un lado, el análisis y comparativa de técnicas de control de emulación de máquinas síncronas para redes ac, donde evaluamos su comportamiento ante diferentes tipos de perturbaciones y examinamos su estabilidad aplicando criterios generalizados de Nyquist. En el ámbito de las redes dc, por otra parte, proponemos nuevas técnicas de control que son análogas a las analizadas para las redes ac, y que denominamos como condensadores-virtuales puesto que emulan el comportamiento dinámico de estos elementos pasivos conectados a la red. En este caso, estudiamos en detalle su comportamiento dinámico y en régimen permanente, demostrando que se pueden adaptar simplemente variando parámetros de control, y analizamos su estabilidad llevando a cabo análisis paramétricos de sus valores propios dominantes

Network Topology Invariant Stability Certificates for DC Microgrids with Arbitrary Load Dynamics

DC microgrids are prone to small-signal instabilities due to the presence of tightly regulated loads. This paper develops a decentralized stability certificate which is capable of certifying the small-signal stability of an islanded DC network containing such loads. Utilizing a novel homotopy approach, the proposed standards ensure that no system eigenmodes are able to cross into the unstable right half plane for a continuous range of controller gain levels. The resulting "standards" can be applied to variety of grid components which meet the specified, but non-unique, criteria. These standards thus take a step towards offering plug-and-play operability of DC microgrids. The proposed theorems are explicitly illustrated and numerically validated on multiple DC microgrid test-cases containing both buck and boost converter dynamics