[en] Electrical power plays a very important role in today's society, but the necessity to reduce the greenhouse gas emissions requires to shift the classical fossil fuel-based power generation towards a renewable based model. In this transition, existing power systems need to embrace significant changes. The operation of renewable-based power systems with a high presence of power converters becomes more challenging since these generators present a reduced inherent inertial response, reduced primary regulation capacity and the power generation is nonschedulable. At the same time, dc power systems are gaining popularity due to the advantages they offer for certain applications. Among the different changes that power systems might undergo in order to make them more controllable, reliable and with a better transient response, it is envisioned that power systems will adopt more modular topologies where different ac and dc subgrids will be combined, forming a grid of grids. In this scenario, interlinking converters (IC)—which are power electronic converters to tie electric grids—will have a key role, since they can be employed to interconnect power systems of different natures and characteristics, and offer a high controllability over the flow of power among subgrids. The main purpose of this thesis is to develop, analyse and validate control strategies for ICs that contribute to the transient response of interconnected ac and dc power systems. In order to achieve this objective, first we propose a power flow-based simulation tool, named dynamic frequency power flow (DFPF). This tool enables to study the dynamic behaviour of ac, dc and hybrid power system scenarios, and the contribution of ICs and their controls to the transient response of interconnected systems. Then, after carrying out a literature review, two IC controls are proposed in this document. The first technique is named as dual inertia-emulation (DIE) control, and it provides inertial response for both interconnected grids, contributing to improve both systems' inertial response. The second technique corresponds to a virtual power line (VPL) control, and makes the IC behave as a traditional power transmission line but it enables to tie power systems of different characteristics and natures. This technique unifies the interconnected power systems in terms of primary reserve and inertia, so the transient response is improved, and it facilitates the flow of power from generation to loading points in a natural way. Simulation results that validate the contribution of the proposed controls to the transient response of the grids under different test cases are provided throughout the document.

[eu] Energia elektrikoak gaur egungo gizartean garrantzi handia badu ere, berotegi efektua bultzatzen duten gasen isurketa gutxitzeko erregai fosilak alde batera utzi eta energia berriztagarriak erabiltzea ezinbestekoa izango da energia sorkuntza prozesuetan. Hau lortzeko, egungo sare elektrikoek hainbat aldaketa jasan beharko dituzte euren baitan. Energia berriztagarrietan eta potentzia bihurgailuetan oinarritutako sare elektrikoen kudeaketa eta kontrola konplexuagoa da hainbat arrazoi direla medio. Besteak beste, erantzun inertzial urria, erreserba primario mugatua edo potentzia ekoizpenaren ez- programagarritasuna direla medio. Aldi berean, korronte zuzeneko sistemen erabilera areagotzen ari da eta horregatik, sare elektrikoak errazago kudeatu eta euren egonkortasun iragankorra hobetu ahal izateko, hauek egitura modularragoak hartuko dituztela aurreikusten da, non korronte zuzen eta alternoko sare desberdinak elkarren artean loturik egongo diren. Lotura hauetan, ingelesezko interlinking converter (IC)-ek—sare elektriko ezberdinak lotzeko erabiltzen diren bihurgailuek hain zuzen ere—garrantzi handia izango dute. Horregatik, tesi honen helburu nagusia IC bihurgailu bidez loturiko sare elektrikoen portaera iragankorra hobetuko duten kontrol estrategiak proposatu eta balioztatzea izango da. Helburu hau erdiesteko, lehenik eta behin korronte zuzen, alterno, zein sare hibridoen portaera dinamiko eta iragankorra aztertzea ahalbidetuko duen simulazio erreminta bat proposatu dugu. Baliabide honek IC-ek eta hauen kontrolak elkarrekin lotutako sareen erantzun iragankorrari eskaintzen dioten onura zenbatekoa den ebaluatzen lagunduko digu. Bestalde, literaturan topatu diren kontrol desberdinen gaineko azterketa egin ondoren, bi kontrol teknika proposatu ditugu. Lehenak erantzun inertziala eskaintzen die IC aren bi aldetan dauden sareei, honetarako potentzia sare batetik bestera maneiatuz. Bigarren proposamenak, elkarrekin zuzenean konektagarriak diren bi sare lotzen dituen transmisio linea bat bezala lan egitera bultzatuko du IC-a, baina zuzenean konektagarriak ez diren sistemak lotzea ahalbidetuz. Teknika honek bi sareak batu egingo ditu inertzia eta erreserba primarioari dagokionez, beraz sareen erantzun iragankorra hobetzeaz gain potentzia fluxua naturala izango da sorgailu eta karga ezberdinen artean. Proposaturiko kontrolen eraginkortasuna frogatu eta sareen portaera iragankorra hobetzen dutela egiaztatzeko simulazio proba ezberdinak egin dira, eta emaitzak eskuragarri daude dokumentuan zehar.