Retificadores trifásicos baseados em conversores estáticos conectados em série.

Abstract

Three groups of three-phase rectifiers based on series connected static converters are presented in this Masters dissertation, with the objective of contributing to the diversity of options available in the literature. The configurations proposed are analyzed and compared by means of the THD of the currents supplied by the AC power source, the WTHD of the AC voltages generated by the converters, and the conduction and switching losses at the semiconductor elements. The first group, labeled group OE (Open-End), has five configurations based on open-end AC sources, which allow the connection of two three-phase converters in series. The second group, labeled group SCIT (Series Converters with Injection Transformers), has three topologies based on two series connected threephase converters by means of injection transformers. The last group of topologies, labeled group SHB (Series H-Bridges), has six configurations based on two cascaded H-bridges per phase. The first and the second groups contain uni and bidirectional configurations, while the last one has only unidirectional options. A chapter is dedicated to each group of topologies, in which it is covered the electrical models of the systems, the PWM techniques employed and the proposed control strategies. The PWM techniques are based on the LSPWM (Level-Shifted PWM), and the control systems are based on cascaded structures, where the external loop corresponds to the DC voltages regulation and the internal loop corresponds to the AC currents control. Furthermore, simulation and some experimental results are shown and analyzed for every group. The comparisons between the configurations are made by means of simulation results, while the experimental results validate the applicability of the proposed topologies. Another chapter of this work addresses the generalization of groups SCIT and SHB, where the systems models and the preliminary calculations necessary for the development of the PWM techniques are presented for situations in which more than two basic cells of converters are connected in cascade. The final chapter concludes the work comparing the configurations based on the obtained simulation results. It can be concluded that among groups OE and SCIT some configurations within the first group presented the highest levels of THD, WTHD and semiconductor losses. Moreover, it was verified that group SCIT required a simpler control system. Between the configurations of group SHB, a subgroup with three nonisolated DC-links presented lower THD, WTHD and semiconductor losses than the other two subgroups, where one is composed by configurations with only one DC-link and the other is a subgroup with three isolated DC-links.