Conversores PWM multinível com capacitores flutuantes, transformadores em cascata e braços compartilhados.

Abstract

In this Doctoral dissertation, static multilevel power converters are proposed as alter- native solutions with better performance in terms of harmonic distortion, power losses, and switching stress with relation to the considered conventional options. Four groups of converters based on cascaded asymmetrical cells are presented. The Ąrst group uti- lizes an open-end three-phase source to connect two three-phase cells in series with the system, beyond employing H-bridges with Ćoating capacitors in series with the phases. The objective is to show the better performance of proposed unidirectional rectiĄers face to the conventional two-level topology and validate the proposed techniques to regulate the Ćoating capacitors. On the three remaining groups, three-phase converters topologies with three and four wires and single-phase shared leg converters are addressed. On them, transformers with cascaded secondary windings are used to connect the cells in series while using a single dc-link. In these cases, the objective is to demonstrate the converters operation and control simplicity in relation to alternatives with many dc-link capacitors, like the ones in the Ąrst group. Moreover, we want to demonstrate their performance in relation to conventional two-level and multilevel options with one dc-link, to show that proposed conĄgurations can present better performance despite the additional losses com- ponents of the transformers. The analysis and validation methodology consisted in the realization of digital simulations under normalized conditions for all cases, considering as Ągures of merit the harmonic distortion of voltage and current waveforms, the switch- ing frequency and stress, and the semiconductors and total losses of the system under normalized THD conditions. After verifying the simulations performances, the structures were experimentally validated. In general, by means of the results obtained it was veriĄed that proposed conĄgurations could operate with lower harmonic distortion, as well as with lower semiconductors and total losses, besides being capable to operate under lower switching frequency on normalized harmonic distortion conditions, which gives them lower switching stress. Furthermore, in the Ąrst group of conĄgurations the PWM and Ćoating capacitors voltage regulation techniques were validated with success. In the case of the re- maining groups, it could be veriĄed greater simplicity of the control system. Therefore, we conclude that proposed conĄgurations were validated as multilevel alternatives, that the PWM and control techniques utilized were efective, and that the cascaded transformers and shared legs techniques to generate multilevel topologies also have shown good results compared to conventional alternatives.