Inversores multiníveis em cascata usando reduzido número de fontes CC isoladas.

Abstract

This work is focused on the study of multilevel CC-CA converters capable of produces a

high number of output levels using a small number of isolated DC sources and, in gen- eral, number of components. In this context, three topologies based on the Neutral-Point

Clamped (NPC) converter employing a single isolated DC source and two other structures based on the Modular Multilevel Cascaded Converter (MMCC). Systems based on NPC

converter consist of multilevel inverters with cascaded transformers coupled only to three- level NPC legs or associated with three-level NPC legs and two-level legs, where one of

them is shared between transformers. These conĄgurations are analyzed considering two scenarios of transformers, one symmetric and another one asymmetric. Systems based on MMCC converter consist of asymmetric cascaded multilevel inverters, where each phase is composed of a three-level H-bridge and a nine-level H-bridge connected in series. The nine-level H-bridges are constructed from the MMCC, while the three-level H-bridges are

operated in two ways, or using DC source and or using Ćoating capacitor. These conĄgu- rations are investigated using the asymmetric DC voltage ratios of 1:8 and 1:12 between

the H-bridges. For one of these topologies, an operation analysis of the converter and the stress equations that describe the system model are presented. From the analysis of possible combinations of swicthing states, modulation strategies are also developed. In

addition, are used to compare and evaluate the performance of the topologies investi- gated the following main criteria: number of components and levels; nominal power of the

transformers; voltage, current and rated frequency of the power switches, total harmonic distortion (THD); losses in semiconductor devices and transformers; and common mode voltage. Finally, the simulation and experimental results are presented and discussed for the validation of the topologies studied.