Technology Comparison for Cascaded Multilevel Converters in Distribution Networks

This paper compares technology for two structures of cascaded multilevel converter for 11kV and 33kV distribution networks on the basis of power losses in IGBT. First, is traditional cascaded converter which has equal-sized cells in its chain and the other is the recently proposed chain with a ternary relationship between its dc-link voltages. Models with 81 and 27 levels are developed for both kinds of converter after selection of suitable IGBT device technology for comparative analysis. The total power losses in IGBTs and diode of each cell in the chain are estimated by simulation and it has been concluded that conduction losses are dominant everywhere. The equal-sized converter is only useful with 27-levels in 33kV system whereas the ternary-sequence converter produces lower losses in the other cases and especially so for the 81-level converter in the 11kV network.