Estratégias de modulação para conversores multiníveis com capacitores flutuantes

Abstract

This Thesis contributes to the modulation of the multi-level three-phase converter with flying capacitors, for which simulations were performed to validate three different modulation algorithms. The first one is a phase shift modulation. In order to regulate the voltage of the flying capacitors, a proportional control loop was used that displaces the modulating one, causing the charging or discharging time in a given capacitor to be altered, thus making it possible to control the voltages in the flying capacitors. The second modulation technique was based on a discontinuous modulation. Through discontinuous modulators that vary between regions of PWM and saturation. It is proposed the alternation between the modulating signals that allows the average current in the flying capacitors to remain around zero without increasing the number of commutions. In addition, a proportional controller was implemented to regulate the voltages of the flying capacitors. The main advantage of this technique when compared to phase shift modulation is the reduce THD of line-to-line voltages. Then, a space vector modulation for FCC is proposed. In this modulation, diagrams were created to help definition of the switching sequences for the sectors of the vector space. For each sector, seven sequences were created, in which the first sequence is chosen among the vectors ina a way that at the end of the sequence none of the flying capacitors charged or discharged, plus two more sequences for each flying capacitor. These two sequences serve to regulate the voltage in each flying capacitor, one of them charging and the other discharging the flying capacitor, thus it is possible to maintain the regulated voltages. A fare comparison was then made between the modulation techniques. Initially, it was in order to take care to ensure equality between modulations, such as using the same simulation parameters and the same number of commutations per sampling period. Thus, the performance of the modulations by THD and the first order distortion factor for the modulations addressed in this work were analyzed.