Estudo de balanceamento de capacitor flutuante e regeneração de potência para inversores multiníveis monofásicos baseados em ponte-H em cascata.

Abstract

This work consists of the study, characterization, and analysis of single-phase multi- level converters based on Cascaded H-Bridge topology. Two groups of configurations are presented, whose dc-links are formed exclusively by dc-sources or by dc-sources and a floating capacitor. In this work, these configurations may have two or three converters in series. In the configuration composed of only dc-sources, there may be power exchange between the converters, which leads to a bidirectional power flow for some modulation index values and some dc-link voltage ratios, regardless of the load power factor. Considering this, switching strategies are presented for applications where regenerative mode operation is not allowed, forcing all cells to have a unidirectional power flow and towards the load. In this way, Cascaded H-Bridge and its various cases of dc-link voltage ratio are discussed and compared using criteria such as power distribution in each cell, semiconductor power losses, switching frequency and harmonic distortion. In relation to the Cascaded H-Bridge with capacitors, two methods are presented to regulate the floating capacitor voltage by employing redundancies or degrees of freedom. Power distribution in the cells with capacitive dc-link is analyzed according to the voltage balancing technique used and in accordance with the variation of the power factor and modulation index values. In addition, a capacitor voltage control is developed for a three-stage inverter, so that smooth control actions are imposed to minimize spikes, ripple and THD at the output voltage of the system and to ensure voltage regulation of the floating capacitor. Experimental implementations and computational simulations were used to verify the presented considerations and to show the feasibility of the systems presented in this work.