Seok-Min Kim, June-Seok Lee, and Kyo-Beum Lee, "A Novel Modulation Method for Half-Bridge Based Modular Multilevel Converter under Submodule Failure with Reduced Switching Frequency," in Proc. APEC Conf., Mar. 2019, pp. 620–624. > Paper

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.