Fault-Tree-Based Failure-Rate Analysis for Clamped-Double Submodule Employing dc-Short Current Protecting Function

Clamped-double submodule has dc short current protecting function, which can improve safety and stability of HVDC system. However, it needs additional IGBT, diode, and capacitor compared to the conventional half-bridge and full-bridge submodules. Generally, the failure-rate increases in proportion to the number of circuit components. Complex operation of the submodule may increase the failure-rate, so accurate reliability analysis is required to apply CDSM in practical HVDC system. Fault-tree-based reliability analysis is performed to take into account the operational characteristics of CDSM. FTA is possible to analyze the failure-rate more accurately than the prior PCA that considers only the type of parts, the number of parts, and the connection status. By comparing the failure-rate of a CDSM with typical HBSM and FBSM, and analyzing the failure-rate according to the voltage margin of the parts, it provides guidelines for submodule selection under various conditions.