Fault-Tolerant Oriented Hierarchical Control and Configuration of Modular Multilevel Converter for Shipboard MVdc System

Medium-voltage dc (MVdc) distribution system is considered as the promising power architecture of future shipboard power system. Fault-tolerance ability is of great importance for power system on ships. In this paper, zonal dc-dc conversion system based on modular multilevel converter (MMC) and three-phase bridge rectifier are proposed with its hierarchical fault-tolerant scheme. The topology configurations of the front-end MMC with multiwinding medium frequency transformer under normal and postfault circumstances are presented. The reconfiguration scheme and fault-tolerant control strategy are also proposed to ride-through submodule (SM) level fault, phase level fault and bus level fault. Based on the hierarchical fault-tolerant scheme, redundant configuration of the MMC SM is further analyzed with the hierarchical reliability modeling. The effectiveness of the proposed control strategy is verified by the experimental results.