Redundancy design for modular multilevel converter based STATCOMs

Many strategies have been proposed to improve the reliability of Modular Multilevel Converters (MMCs). However, the redundancy factor selection to support a converter fault tolerance operation is an important field to be explored. This work proposes a combined reliability model for the correct selection of the additional number of cells to achieve a target lifetime. This model combines both wear-out and random failures data and compute the required redundancy factor for a given reliability target. The proposed model is evaluated through a reliability-oriented case study, whereas four device voltage classes in a 13.8 kV/17 MVA MMC STATCOM are considered.