Multilevel Converter for 4.16- and 6.6-kV Variable Speed Drives

This article presents a new transformerless multilevel converter topology. This power converter is owned by Nidec ASI and is implemented in the medium-voltage drive SILCOVERT-FH. The topology is composed by the series association of two Macro cells, which can be extended in order to increase the number of output levels, and one external selector cell. Among the advantages, the number of devices directly connected in series does not depend on the dc bus voltage. The same devices can be used in 5L and 7L configurations to address the 4.16- and 6.6-kV applications, which is a significant advantage from the industrialization point of view. Moreover, due to its inherent feature, the zero-crossing is performed naturally at zero-voltage switching on the selector cell. Experimental and simulation results are shown in order to validate the performance of the converter, highlighting the main benefits and features of the proposed topology.