[en] The current society is facing several challenges in terms of energy, such as the high dependency on fossil fuels, the high rate of reliance on imported energy, 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 energy sources (RES), is the most interesting solution to address these issues. However, the penetration of RES into the power grid implies certain challenges due to their non-dispatchable nature compared to conventional generation systems. Such systems often use power electronic converters for grid connection instead of synchronous generators, making power systems become converter-dominated. As the power electronic converterbased grid makes it increasingly necessary to employ power equipment with higher voltage and power rating, since their scalable attributes, multilevel Voltage Source Converters (VSCs) based on modular structures are envisioned as the most promising alternatives for that purpose. In this framework, Flexible AC Transmission System (FACTS) devices, and in particular Static Synchronous Compensators (STATCOMs), play a key role in the evolution of the modern power grids to the future smart grids. The STATCOM, especially the one which employs multilevel VSCs based on modular structures, is applied in an increasingly wider variety of scenarios in which the operation under negative-sequence voltage and/or current conditions stands out. From the power converter manufacturer point of view, it is not obvious which VSC topology should be used. That is why the purpose of the thesis is to contribute to the body of knowledge in the field of the design of VSCs, with the aim of facilitating the manufacturer to compare and select the most appropriate topology, to design it properly, or to adapt it in order to face the demanding operating requirements that a converter-dominated power grid implies. Among these, this work is mainly focused on the STATCOM application of multilevel VSCs based on modular structures operating under unbalanced voltage and/or current conditions. To achieve this goal, the operation of the most commonly used high power – MV VSC topologies and their main modulation strategies are first reviewed. Secondly, a methodology which provides valuable information that allows the converter manufacturer to compare and select the most suitable VSC topology for any required application is proposed. Then, a comprehensive review about the operation of multilevel VSCs based on modular structures for different and equivalent unbalanced operating scenarios is presented, in which the STATCOM functionality is included. Having identified the research gap, the reactive power limits of different VSC topologies for STATCOM application operating under unbalanced voltage and/or current conditions are studied and compared. Finally, the control implementation of one of the most interesting topologies for the application under study is evaluated, comparing the performance of different regulators that could be employed. Experimental results obtained from a real-scale 100 kVA prototype in a MV laboratory validate the carried out studies.

[eu] Gaur egungo gizartea energiaren arloko hainbat erronka garrantzitsuren aurrean aurkitzen da, besteak beste, erregai fosilekiko menpekotasun handia, inportatutako energiarekiko dependentzia, kontsumo energetikoaren etengabeko gorakada, edota faktore hauek eragiten dituzten ingurumen arazoak. Sorkuntza banatuko sistemen integrazioa, bereziki iturri berriztagarrietan oinarritutakoa, arazo horiei aurre egiteko aukera interesgarriena da. Hala ere, bere izaera kudeaezina dela eta, sorkuntza berriztagarria sare elektrikoan integratzeak zenbait erronka dakartza ohiko sorkuntza sistemekin alderatuta. Gainera, iturri berriztagarrien sistemek, sorgailu sinkronoen ordez, potentzia bihurgailu elektronikoak erabiltzen dituzte sarera konektatzeko. Bihurgailuak nagusi diren sare elektrikoak tentsio eta potentzia handiagoko gailuak erabiltzea eskatzen du, eta horretarako, tentsio iturridun bihurgailu (VSC) multinibel modularrak alternatiba erakargarrienetariko bat dira. Testuinguru honetan, "FACTS" bezala ezagutzen diren korronte alternoko transmisio gailuek, eta bereziki konpentsatzaile sinkrono estatikoek (STATCOM), funtsezko eginkizuna dute sare elektriko modernoen eboluzioan etorkizuneko sare adimendunerantz. STATCOMak, batez ere VSC bihurgailu multinibel modularretan oinarrituta daudenak, gero eta aplikazio ugariagoetan erabiltzen dira, non tentsio eta/edo korronte desorekatuen aurrean funtzionatzea nabarmandu daitekeen. Bihurgailu fabrikatzailearen ikuspuntutik, ez da hain agerikoa zein VSC topologia erabili behar den. Hori dela eta, doktorego tesi honen helburua VSC diseinuaren alorreko ezagutzan laguntzea da, fabrikatzaileari topologiak konparatu eta egokiena hautatzen errazteko, era egokian diseinatzeko, edota egokitzapenak egiten laguntzeko helburuarekin, bihurgailuek dituzten eskakizun zorrotzei aurre egiteko. Eskakizun horien artean, tesi hau VSC bihurgailu multinibel modularrez eraikitako STATCOM-en tentsio zein korronte desorekatuen funtzionamenduan zentratzen da. Helburu hori betetzeko, lehenik eta behin, potentzia handiko erdi-tentsioko VSC topologien eta haien modulazio estrategia nagusien funtzionamenduari buruzko ikerketa bat garatzen da. Bigarrenik, metodologia bat proposatzen da, bihurgailu fabrikatzaileri behar duen edozein aplikaziorako VSC topologia egokiena konparatu eta hautatzeko informazio baliagarria eskaintzen diona. Jarraian, VSC bihurgailu modular multinibelen funtzionamendu desorekatu desberdinei buruzko literatura zientifikoaren errebisio bat egiten da, STATCOM-aren funtzionalitatea barne. Ezagutza hutsunea identifikatu ondoren, tentsio eta/edo korronte desoreken aurrean funtzionatzen duen STATCOM aplikaziorako VSC topologia desberdinen potentzia erreaktiboaren mugak aztertu eta konparatzen dira. Azkenik, aztergai dugun aplikaziorako topologia interesgarrienetariko baten kontrol inplementazioa ebaluatzen da, erabil daitezkeen kontroladore desberdinen portaera aztertu eta konparatzen delarik. Erdi-tentsioko laborategi batean, 100 kVA-ko eskala errealeko bihurgailu batetik lortutako emaitza esperimentalek egindako azterketa teorikoak balioztatuko dituzte.