Reliability Calculation of Multilevel Converters: Theory and Applications

Multilevel converters have many power devices and drivers. Thus, a direct reliability calculation based only on the first failure occurrence on one of the components clearly leads them to be devalued compared to two-level converters. However, taking into account that symmetrical multilevel converters such as the X-level active neutral point clamped (ANPC) family are based on imbricated and/or stacked switching cells on the one hand, with an additional center tap at the dc bus in three-phase operation on the other hand, several redundancies clearly appear which can be managed to increase the global reliability. For the first time, a general and theoretical methodology used to calculate reliability laws and failure rates and applied to compare two-, three-, and five-level topologies is proposed. Results show that the fault handling of three- and five-level three-phase topologies permits a great increase in reliability over a “relatively” short time duration, in addition to other benefits.