Robust Submodule Fault Management in Modular Multilevel Converters With Nearest Level Modulation for Uninterrupted Power Transmission

The modular multilevel converter (MMC) is widely used in high and medium voltage applications. To improve the reliability of the MMC, fast and accurate submodule (SM) fault detection, location, and tolerant control are required to avoid the interrupted power transmission. Existing methods do not consider all fault characteristics of SM in different operation modes when MMC adopts nearest level modulation. This paper proposes a robust SM fault management scheme that enables uninterrupted operation of MMC with nearest level modulation under SM fault. The SM fault characteristics in different operation modes are presented. Then, the fault detection method based on measuring the compensation of the circulating current suppression controller is proposed. Three quantities, including accumulated discharge voltage, unbalanced charge voltage and capacitor voltage, are used to locate the faulty SM and identify the fault type. In addition, a fault-tolerant control method is proposed by injecting a symmetry compensation component into the modulation signals. Finally, simulation and experimental results are presented to verify the proposed fault detection, location and tolerant control methods.