Asymmetrical Cascaded Three-Phase AC-DC Converters with Injection Transformers

In this paper, three configurations of three-phase ac-dc cascaded converters are presented. They are referred as basic configurations, and are composed by two three-phase bridges, where the second bridge is cascaded to the first by means of a three-phase injection transformer. Basic configurations have one bidirectional option (composed only by IGBT switches), and two unidirectional ones (composed by IGBT and diodes). Their generalizations, which are composed by an indefinite number of cascaded three-phase bridges, are also proposed. Each additional cascaded bridge is a three-phase IGBT bridge and requires one additional three-phase injection transformer. Transformers turns ratios are calculated in order to maximize the number of levels produced in the ac side of each rectifier, enhancing power quality. Basic configurations are compared by means of simulations between themselves and with the conventional three-phase IGBT bridge, to show that proposed multilevel rectifiers present better performance in terms of ac power quality drew from the ac source, with lower semiconductor losses. Experimental results are also exposed for the basic configurations to validate them and show their feasibility.