Novas topologias de inversores multiníveis baseadas na célula de comutação de três estados

Abstract

Multilevel inverters have been widely investigated due to their ability to reduce harmonic distortion, decrease electrical stresses on power semiconductor devices, and improve the quality of the energy delivered to the load. However, many multilevel architectures exhibit high structural complexity and require a large number of active components. In this context, this thesis employs the duality principle between voltage-source and current-source converters in the development of topologies based on the three-state switching cell (3SSC), in which the integrated autotransformer constitutes an intrinsic part of the cell and promotes current sharing between its branches. Based on this approach, two single-phase multilevel topologies are proposed: the CSI 5L-3SSC and the VSI 5L-3SSC. In the proposed structures, multilevel synthesis is achieved using a single 3SSC operating at high frequency, responsible for generating the intermediate levels of the output voltage or current, combined with a complementary leg composed of two switches operating at low frequency to reverse the output polarity. This configuration concentrates high-frequency switching operation in the 3SSC. The integrated autotransformer promotes natural current sharing among the branches, reducing the current conducted by each device and increasing the current processing capability of the topology. In addition, the interleaved operation of the high-frequency switches doubles the effective frequency of the switching-frequency spectral components at the output, reducing filtering requirements. For the CSI 5L-3SSC, the inherent step-up characteristic of currentsource converters enables the connection of low-voltage sources without the need for multiple series-connected modules or an intermediate DC-DC conversion stage. For the VSI 5L-3SSC, qualitative and quantitative analyses are carried out, including switching-state analysis, space vector modulation, and analytical expressions for RMS voltages and currents, electrical stresses, losses, and efficiency. The analytical model supports the implementation of an experimental prototype operating with an input voltage of 240 V, switching frequency of 10 kHz, and fundamental frequency of 60 Hz, whose results confirm the synthesis of five output voltage levels and a maximum efficiency of approximately 97 %. The architecture is further generalized into a seven-level VSI configuration validated through simulation, demonstrating the possibility of systematic expansion through the multistate switching cell (MSSC).