Open-circuit Failure Detection and Localization of Full-bridge Submodules for MMCs with Single Ring Theorem

The full-bridge submodule (FBSM) is regarded as an ideal submodule topology for the MMC due to its bidirectional current blocking capability. Compared with the half-bridge submodule (HBSM), the FBSM has more switching devices and is more prone to failure. Upon FBSM open-circuit failures, faulty FBSMs have higher average capacitor voltages than normal FBSMs. Hence, detection of FBSM open-circuit failures can be implemented with capacitor voltage consistency evaluation. To evaluate capacitor voltage consistency of numerous FBSMs efficiently in the MMC, the single ring theorem is applied to FBSM open-circuit failure detection in this paper. Besides, a statistical failure localization method is also proposed to identify faulty FBSMs. The proposed method requires no system information in advance and thus is immune to parameter uncertainties. No extra hardware is needed and the proposed method is compatible with various failure scenarios. Experimental results on a 13-level three-phase MMC prototype are proposed to verify the effectiveness of the proposed method under various failure scenarios.