| Resumo: |
This works proposes the conception of single-phase and three-phase AC-DC converters based on the modified multi-state switching cell type T (MSSC-TTM), which can be applied in medium-voltage systems. The converters under study can be employed as the input stage of systems composed of multilevel Neutral Point Clamped (NPC), Modular Multilevel Converters (MMC) and and/or cascade full-bridge (H bridge) inverters. Such structures are adequate for a wide variety of applications, e.g., induction motor drives, uninterruptible power supplies (UPSs), active filters, among others. The versatility of the aforementioned structures is owing to the MSSC-TTM, which incorporates a transformer to which secondary windings with proper turns ratio are coupled according to the requirement. Other prominent characteristics include power factor correction; achievement of balanced multiple output voltages; multilevel voltage waveforms on the input downstream of the inductor; and reduced voltage stresses on the semiconductors, which are lower than the total dc link voltage, with consequent impact on the efficiency. After proposing topologies of three-phase and single-phase bidirectional AC-DC converters, and due to the extension of the theme, the thesis was limited to the study of two single-phase topologies derived from generic topologies, one not isolated and one isolated. For the aforementioned topologies, qualitative analysis, quantitative analysis and plant modeling were performed to obtain transfer functions by the approximate method. In order to verify the operating principle, power and control circuits were designed for 110 V input voltage, 1 kV total output voltage distributed over four 250 V outputs and 3 kW total output power. The results showed that by just balancing the output voltages of the type T cell, the outputs of the coupled secondary cells are naturally balanced. |
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