Thyristor-Inserted MMC Sub-Module Topology with DC Fault Blocking Capability

Abstract

Modular multilevel converter (MMC) is increasingly being applied to high voltage direct current (HVDC) systems. However, dc short circuit situations restrain the application of a conventional half bridge MMC system. In this paper, a new sub-module topology with inserted thyristor can help the MMC system clear a dc side fault. Working states and devices voltage stress of the proposed topology are analyzed and the conduction loss comparison between the proposed topology with several existing topologies with dc fault blocking capability is carried out. Results show the proposed topology is superior to other topologies in terms of conduction loss while using the same voltage rating devices. Besides, compared with traditional half bridge topology, only thyristors and diodes are added in the proposed topology. Therefore, cost of the proposed topology can be lower than conventional hybrid MMC sub-modules. At last, the fault blocking capability of the proposed topology is verified in the simulation.

Keywords

• Fault current limiting
• high voltage direct current (HVDC) transmission
• modular multilevel converter (MMC)