Estudo das estratégias de modulação para conversores três níveis do tipo NPC.

Abstract

This work presents a, study of modulation strategies for three-level converters with diode neutral point clamped. Por proper operation of this type of converter the voltage balance of the de-link capacitors must be maintained. In order to obtain better performance of the multilevel converter a survey of the PWM strategies for these structures was made, pointing out some peculiarities of each. Five strategies are analyzed, three of which operate in closed-loop and two in open-loop. A new closedloop strategy was designed, improving voltage balance and output THD at low switching frequencies (720Hz), when compared with the other strategies under study. To define the choice of modulation strategy that has better performance, some factors will be considered: which minimum frequency the converter can work without affect your income, operating under load unbalanced, levels of distortion of currents and voltages, and as the losses generated by the switching and conduction. This work presents simulation and experimental results. To test some of these strategies was mounted the structure of a converter with six branches with three levels clamping diodes, the new module using the multilevel SEMIKRON. A digital signal processor was used to generate the command signals from the devices and fiber-optics, to avoid interference. This work also provides an introduction to the converter Back-to-Back three levels.