Reliability-Oriented Design of Modular Multilevel Converters for Medium-Voltage STATCOM

Modular multilevel converters (MMC) are complex systems, composed of many elements, and exposed to critical load demands in some cases. Thereby, a detailed design of its components is of preeminent importance to achieve a high system-level reliability. However, the high number of devices challenges the tradeoff between cost and reliability. This article, introduces a reliability-oriented design methodology, based on the cost to achieve a predefined unreliability level (U∞). A flowchart presents the main steps of the process, including the mission profile definition, selection of power devices, thermal modeling, reliability modeling, and the reliability-oriented selection. To evaluate the proposed methodology, a case study considering 17 MVA/13.8 kV MMC-static synchronous compensator (STATCOM) with a real mission profile data is conducted. A U∞- cost map is introduced to compare various design solutions, based on power devices of different voltage classes and current capabilities.