A fault tolerant control for modular multilevel converter under submodule fault conditions

The modular multilevel converters become more and more popular in high power applications in recent years. The solution to make the MMC operate well under the submodule failure is a key technology to increase reliability of the MMC-based systems. In this paper, a fault tolerant control method based on the zero-sequence voltage injection is proposed to maintain stable line-to-line voltage under submodule fault conditions. The proposed method can make full use of un-faulty submodules and reduce the negative influences caused by the submodule failure. In addition, the proposed method is with simple implementation and easy to be executed in digital controllers. Comparative analysis between the proposed method and one conventional method is carried out from the aspects of the harmonic characteristics, dynamic-state characteristics. Finally, the effectiveness of the proposed control method is verified by experimental results.