This paper proposes a novel modulation method for half-bridge submodule (SM) based modular multilevel converter (MMC) under faulty SM condition. When a SM is failed, the proper healthy SM is selected and the faulty SM is replaced by the healthy SM in the proposed fault-tolerant method. By replacing the faulty SM, the MMC continues its operation as the normal mode. The SM selection is implemented by a novel modulation method and it reduces the switching frequency of all healthy SMs, which is the serious drawback of the conventional sorting algorithm. The neutral-shift method is applied in order to maintain the balanced three-phase line-to-line voltages during a fundamental period. Various simulation studies verify that this post-fault strategy guarantees the balanced three-phase line-to-line voltages and currents as well as balancing of SM capacitor voltages without the aid of extra SMs.
This research was supported by the KEPCO Research Institute under the project entitled by \u201cDesign of analysis model and optimal voltage for MVDC distribution system (R17DA10)\u201d
