Sistema de conversão de energia multiníveis CA/CC/CA e CC/CA.

Abstract

This work consists of the study, characterization, and analysis of new topologies and control techniques of AC/DC/AC and DC/AC multilevel energy conversion systems. The main motivation is to find configurations with 1) lower voltage harmonic distortion; 2) lower semiconductor losses; 3) components with lower rating; and 4) lower cost, in the case of the unidirectional converters. The studied AC/DC/AC converters generate voltages with low harmonic distortions and constant amplitude and phase and keep the grid current sinusoidal and with high power factor. These converters can be utilized in UPS and UPQC applications. Considering the AC/DC/AC systems, three types of converters are studied: 1) single-phase to single-phase unidirectional; 2) single-phase to single-phase bidirectional; 3) single-phase to three-phase bidirectional. Two AC/DC/AC single-phase to single-phase unidirectional converters are proposed and one of them has similar performance and lower cost than the conventional one. Two AC/DC/AC single-phase to single-phase bidirectional converters are proposed. Both converters can be used to mitigate fundamental overvoltage and voltage harmonics at the grid. One converter accomplishes this using a line frequency transformer and the other using an H-bridge. Compared with the conventional configurations, the proposed ones have lower switching and higher conduction losses. Two AC/DC/AC single-phase to three-phase bidirectional are studied. They are more interesting for applications in which grid and load fundamental frequencies are the same. Compared with the conventional topologies and operating with the load voltage equal to approximately half the amplitude of the grid voltage, these converters decrease the voltages and the power processed by the switches, the total harmonic distortion with the same sampling frequency and the switching and total losses. Considering the DC/AC systems, multilevel single-phase inverters with cascaded transformers are studied. The proposed topology is a single-phase topology with two dc links and two shared legs. A generalized model of the topology is presented followed by the calculation of its parameters to maximize the number of equally spaced voltage levels. Compared with the conventional topologies, the proposed one has more levels per transformer/leg when the configurations have the same number of legs/transformers, and has lower switching and higher conduction losses. The AC/DC/AC and DC/AC configurations are analyzed and compared considering, for example, the number of dc links, dc-links voltages values, harmonic distortion of the generated voltages, and semiconductors conduction and switching losses. The regions of operation of the converters are presented. The control systems of the studied converters are presented and the control of the dc-links voltages is highlighted. Experimental results are provided to prove the theoretical results and the viability of the systems.