A Submodule Fault Tolerance and DC Fault Handling Method Based on Novel Topology for Hybrid Modular Multilevel Converters

The submodule (SM) faults and DC faults are the key issues to the security and reliability of modular multilevel converters (MMCs) in high-voltage applications. In this paper, a novel submodule (SM) topology with SM fault tolerance and DC fault blocking is proposed to tackle different faults. Moreover, the diverse operation styles and related regulation methods are also designated for the new SM in various fault cases. In terms of SM fault tolerance, the method based on new SMs realizes the same functions as the conventional methods but affords better perform- ances, such as faster initiation, less operation interference, lower fault risk, easier realization and stronger fault-tolerant capability. Besides, the MMC containing the proposed SMs can clear the DC fault current effectively regardless of the normal mode or the fault-tolerant mode that the proposed SMs stay in. Furthermore, for the hybrid MMC, the proposed SMs are not only beneficial to lower the loss and cost, but also in favor of enhancing the fault- handling property. The operation feasibilities of the hybrid MMC containing the new SMs under different fault cases are verified by the simulation studies with Matlab/Simulink.