Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The multicell inverter, being a widely used multilevel converter, has received much attention in recent years due to problems associated with cell capacitor voltage. In this dissertation we study the balancing problem with a focus on steady-state unbalance. This is achieved by systematic and mathematically rigorous study of the natural balancing mechanisms of the three-phase 2-cell and 3-cell multicell converter, undertaken by using dynamic modelling of the multicell converter, Bennet’s geometric model, steady-state and time constant analysis. Space vector analysis is also performed for the three-phase 2-cell multicell converter. The theory is verified by comparing theoretical results with simulation results / AFRIKAANSE OPSOMMING: Die multisel omkeerder as algemeen-gebruikte meervlakkige omsetter het die afgelope jare groot belangstelling gewek op grond van die probleme wat met selkapasitor stroomspanning geassosieer word. In hierdie proefskrif word die balanseringsprobleem met die klem op die ewewigswanbalans bestudeer. Dit is verrig deur ’n sistematiese en streng wiskundige studie van die natuurlike balanseringsmeganismes van die drie-fase 2-sel en 3- sel multisel omsetter te maak. Dit is gedoen deur die gebruik van dinamiese modellering van die multisel omsetter, Bennet se geometriese model, ewewigtoestand tydkonstante analises, en ruimtevektoranalise is vir die drie-fase 2-sel multisel omsetter gedoen. Die teorie word bevestig deur die teoretiese resultate met die simuleringsresultate te vergelyk

Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / AFRIKAANSE OPSOMMING: Hierdie proefskrif handel oor die natuurlike balanserings meganismes van veelvlakkige en modulêre omsetters wat fase-skuif dragolf puls wydte modulasie gebruik. Die meganismes kan in twee hoof groepe verdeel word: ‘n swak balanserings meganisme wat afhanklik is van die oorvleuling van die skakelfunksies en ‘n sterk meganisme wat voorkom ongeag of die skakelfunksies oorvleul al dan nie. Die sterk meganisme verdeel verder in twee subgroepe, ‘n direkte oordrag van onbalans energie en ‘n meganisme wat afhang van die verliese in die stelsel. Elkeen van die meganismes word aan die hand van ‘n omsetter topologie waarin die spesifieke meganisme oorheers beskryf en ontleed. In die ondersoek word klem geplaas op die daarstelling van uitdrukkings om die tydskonstantes van herbalansering na ’n afwyking vir elk van die omsetter toplologieë te beskryf. / ENGLISH ABSTRACT: This thesis investigates the natural balancing mechanisms in multilevel and modular converters using phase shifted carrier pulse width modulation. Two groups of mechanisms are identified; a weak balancing mechanism that is only present when the switching functions are interleaved and a strong mechanism that occurs irrespective of the interleaving of the switching functions. It is further shown that the strong balancing mechanism can be divided into a balancing mechanism that depends on the direct exchange of unbalance energy and a loss based balancing mechanism. Each of the mechanisms is discussed and analysed using a converter where the specific mechanism dominates as example. Emphasis is placed on the calculation of the rebalancing time constant following a perturbation. Closed form expressions for the rebalancing time constants for each of the analysed converters are presented.

L'utilisation de systèmes de stockage de l'énergie électrique tels que les batteries nécessite l'assemblage de plusieurs cellules. Comme chacune de ces dernières peut avoir des caractéristiques légèrement différentes ainsi que des conditions d'environnement thermique ou de vieillissement distinctes, l'utilisation d'un système d'équilibrage permettant une bonne gestion de la répartition de l'énergie au sein des éléments qui composent le pack est nécessaire. Les travaux de recherche présentés se rapportent à l'étude et à la conception d'un tel circuit d'équilibrage à base de convertisseurs d'énergie intégrables ainsi qu'aux sollicitations électriques engendrées dans les cellules lors de son utilisation. / To store electrical energy in batteries, the use of multiple cells is needed. Since each of these cells can have slightly different characteristics and also different thermal or aging environmental conditions, a balancing system is required to manage the energy inside the battery pack. The researches described in this document show the study and the design of such a balancing system based on power electronics converters and also the impact of these systems on the electrochemical cells.