Loss Comparison of Different Sub-Module Implementations for Modular Multilevel Converters in HVDC Applications

This paper presents a loss calculation and comparison between different submodule topologies and semiconductor choices for a Modular Multilevel Converter in a 1.1 GW, +/- 320 kV HVDC application. Accordingly, a detailed analysis of the losses for three different M2C implementations using both insulated gate bipolar transistors (IGBTs) and integrated gate-commutated thyristors (IGCTs) is presented. The losses for six different submodule realizations are shown in a loss breakdown in Fig. 7. It shows that the very low conduction loss of the IGCT is to some degree offset by higher switching losses and extra turn-on snubber losses but that the IGCT implementations provide significantly lower losses than their IGBT counterparts. The loss break-down also shows that clamp-double submodules and full-bridge submodules suffer from approximately 25 % and 50 % additional losses respectively as compared to the half-bridge case. An experimental verification of the loss calculations has been performed using a down-scaled M2C prototype. The results show a very good agreement between calculations and measured losses.