Modular Multilevel Converter Using IGCT-based Cross-Connected Modules for Medium Voltage DC Grids

The modular multilevel converter (MMC) using half-bridge submodules (HBSMs) cannot clear the DC-side short-circuit current by itself. Various improved MMC topologies based on clamped circuit have been proposed to provide DC fault blocking capability. The extra conduction loss caused by the extra switches in the clamped circuit is an important concern for choosing converter topology. The combination of cross-connected module (CCM) with HBSMs provides DC fault blocking capability and leads to a low number of extra semiconductor switches. Integrated gate commutated thyristor (IGCT) has superior characteristic of low conduction voltage drop and high blocking voltage rating. In this study, in order to reach lowest extra loss, IGCTs are proposed to be used as the semiconductor switches in the CCM. The topology and operating principle of the proposed IGCT-based CCM (ICCM) are presented. The design of a ±10 kV/10 MW ICCM-MMC is presented and the DC fault clearance characteristic are analyzed. Loss evaluation results show that the ICCM-MMC have the lowest extra loss compared to other MMC solutions with DC fault blocking capability. The DC fault clearance capability of the ICCM-MMC is verified using the simulation results.