Fault-Tolerant Control of Full-Bridge Mmc Operating in Boost Mode for Mvdc Applications

To enable safer and more resilient operation, a full-bridge based modular multilevel converter (FB-MMC) has been proposed for medium voltage direct current (MVDC) applications, owing to its inherent dc-side fault blocking capability. In addition, FB-MMC enables boost mode operation, which allows flexible control in the overmodulation region and facilitates step-down of the de-side voltage. However, the increased number of switching devices in the FB-MMC reduces the reliability of the converter. While previous studies have focused on the external fault management of FB-MMCs, limited attention has been given to internal fault tolerant operation, revealing a critical gap in the existing literature. This paper proposes a fault-tolerant operation for FB-MMC which prevents submodule capacitor voltage rise during an internal fault. Furthermore, the proposed fault tolerant method can maintain the post-fault performance of the FB-MMC same as pre-fault conditions without increasing the overall cost of the MMC by considering any redundant submodules. The present article also explains the relationship between the multiple submodule fault tolerant capability and the overmodulation region of the FB-MMC. The performance of the technique is validated through simulations and experimental tests with the 9-level FB-MMC prototype.