[en] Contemporary society faces significant energy challenges due to the accumulation of greenhouse gases in the atmosphere. This scenario has been driven mainly by the use of fossil fuels for energy generation, population growth and exponential technological development. In response, the scientific community has focused its efforts on reducing dependence on fossil fuels in the energy matrix. In this direction, new non-conventional energy sources, such as wind, solar photovoltaic, and geothermal, have been integrated into the power system. The integration of such renewables into the electricity system is progressively replacing synchronous machine-based generation, resulting in a transformation of the electrical system. The reason is that most non-conventional renewables are connected to the grid via electronic converters, eliminating the rotating components of the system. Converters have the advantage of controlling the bi-directional power flow between the grid and the energy source, thereby reducing power losses and thus providing precise control of the non-conventional renewable sources. Conversely, the increasing integration of such renewables is causing new challenges for the system operation by manipulating the various system dynamics. Consequently, this transformation in the power system is leading to a reduction of the total mechanical inertia supplied by the rotating elements of the synchronous machines. Likewise, the fast converter dynamics means that the classical small and large signal stability studies based on phasor models do not represent the true behaviour of the converter-dominated networks. The reason is that the dynamics of the inverters interact with the grid's passive elements, i.e., transmission lines and loads— endangering the system's stability. Inspired by these challenges, the main objective of this thesis is to analyse the stability and control of the electrical networks strictly dominated by the converters, ensuring their correct operation in terms of transient response and steady state, and avoiding adverse interactions between the converter and the grid. To achieve this objective, initially, a methodology for analysing small- and large-signal stability through accurate models of the inverter-dominated networks using electromagnetic models (EMT) is discussed. Subsequently, the grid-supporting control strategy called "Second-order filter-based inertia emulation (SOFIE)" is proposed to provide frequency support employing primary control, inertia emulation and oscillation damping. The SOFIE control is compared against the classical inertia emulation control in grid-supporting converters, demonstrating that the developed control solves several stability problems caused by the adverse interactions between the inverter controls and the LC resonances of the grid. It is worth mentioning that each of the control strategies developed in this thesis have been carefully designed to improve the stability limits of the power system, as well as to increase the number of converter services in the grid. Among other contributions of this thesis, the small-signal stability based comparison of the various grid-forming control approaches under different network conditions is also highlighted. This class of converters demonstrate the need to improve the damping of power oscillations to increase the stability limits in stiff grids.

[eu] Gaur egungo gizarteak energia-erronka handiak ditu atmosferan berotegi-efektuko gasak metatzen direlako. Eszenatoki hau energia sortzeko, biztanleriaren hazkunderako eta garapen teknologiko esponentzialerako erregai fosilen erabilerak bultzatu du batez ere. Horren harira, komunitate zientifikoak energia matrizean erregai fosilekiko menpekotasuna murrizteko ahaleginak bideratu ditu. Norabide horretan, energia-iturri ezkonbentzional berriak, hala nola eolikoa, eguzki fotovoltaikoa eta geotermikoa, sistema elektrikoan integratu dira. Energia berriztagarri horiek sistema elektrikoan txertatzeak makinetan oinarritutako sorkuntza sinkronoa ordezkatzen ari da pixkanaka, sistema elektrikoaren eraldaketa eraginez. Arrazoia da berriztagarri ez-konbentzional gehienak sarera konektatzen direla bihurgailu elektronikoen bidez, sistemaren osagai birakariak ezabatuz. Bihurgailuek sarearen eta energia iturriaren arteko noranzko biko potentzia-fluxua kontrolatzeko abantaila dute, eta, horrela, potentzia-galerak murrizten dituzte eta, horrela, iturri berriztagarri ez-konbentzionalen kontrol zehatza eskaintzen dute. Aitzitik, berriztagarri horien gero eta integrazioa sistemaren funtzionamendurako erronka berriak eragiten ari da sistemaren dinamika ezberdinak manipulatuz. Ondorioz, potentzia-sistemaren eraldaketa honek makina sinkronoen elementu birakariek ematen duten inertzia mekaniko osoaren murrizketa dakar. Era berean, bihurgailu bizkorreko dinamikak esan nahi du fasore ereduetan oinarritutako seinale txiki eta handien egonkortasunaren azterketa klasikoek ez dutela bihurgailuek menperatutako sareen benetako portaera adierazten. Arrazoia da inbertsoreen dinamikak sareko elementu pasiboekin, hau da, transmisio-lerroekin eta kargarekin elkarreragiten duela— sistemaren egonkortasuna arriskuan jarriz. Erronka hauek bultzatuta, tesi honen helburu nagusia bihurgailuek zorrozki nagusi diren sare elektrikoen egonkortasuna eta kontrola aztertzea da, haien funtzionamendu zuzena bermatuz erantzun iragankorrean eta egoera egonkorrean, eta bihurgailuaren eta bihurgailuaren arteko interakzio kaltegarriak saihestuz. sareta. Helburu hori lortzeko, hasiera batean, eredu elektromagnetikoak (EMT) erabiliz inbertsoreak nagusi diren sareen eredu zehatzen bidez seinale txiki eta handien egonkortasuna aztertzeko metodologia bat aztertzen da. Gerora, "Bigarren ordenako iragazkietan oinarritutako inertziaren emulazioa (SOFIE)"izeneko sarearen euskarriaren kontrol-estrategia proposatzen da, maiztasun-euskarria emateko, kontrol primarioa, inertziaren emulazioa eta oszilazio moteltzea erabiliz. SOFIE kontrola sarearen euskarria duten bihurgailuetan inertziaren emulazio kontrol klasikoarekin alderatzen da, garatutako kontrolak inbertsorearen kontrolen eta sarearen LC erresonantziaren arteko interakzio kaltegarriek eragindako egonkortasunarazo batzuk konpontzen dituela frogatuz. Aipatzekoa da tesi honetan garatutako kontrolestrategietako bakoitza arreta handiz diseinatu dela potentzia-sistemaren egonkortasunmugak hobetzeko, baita sareko bihurgailuen zerbitzuen kopurua handitzeko ere. Tesi honen beste ekarpen batzuen artean, sare-baldintza desberdinetan sareak eratzeko kontrol-ikuspegi ezberdinen arteko seinale txikian egonkortasunean oinarritutako konparaketa ere nabarmentzen da. Bihurgailu-klase honek potentzia-oszilazioen moteltzea hobetzeko beharra erakusten du sare zurrunetan egonkortasun-mugak handitzeko.