Reliability Analysis and Redundancy Configuration of MMC With Hybrid Submodule Topologies

Modular multilevel converter (MMC) has become the most promising converter technology for high-voltage direct current (HVdc) transmission systems. MMC submodule (SM) topologies with dc fault ride-through capabilities are emerging which are suitable for overhead line applications. The hybrid SM design of each converter arm can get the compromise of higher capability of handling dc fault and lower capital investments and losses. In this paper, the initial hybrid SM numbers design method for supporting the dc-link voltage and riding-through dc faults and the optimized hybrid SM redundancy configuration strategy for effectively increasing the reliability of MMC are proposed and calculated. In contrast with the previously proposed redundancy configuration for MMC with the single SM topology, this approach solves the curvature of three-dimensional surface to calculate the recommended redundant hybrid SM numbers which takes both the semiconductor device utilization rate and the reliability of MMC into consideration.