A new fault-tolerant realization of the active three-level NPC converter

The three-level (3L) neutral-point-clamped (NPC) voltage-source (VSC) converter has been the standard solution in medium-voltage range for industrial applications. Recently, the NPC converter structure was improved by adding two extra active switches per phase leg, thus overcoming one of its main drawbacks: the unequal power loss among the power semiconductors. The resulting structure became known as active NPC (ANPC) converter. The high availability of these power converters is mandatory, since their maintenance or replacement imply equipment downtimes incompatible with the requirements of the production processes. The fault-tolerant operation of such converters has been addressed in the technical literature, but the main proposed solutions result in more complexity and higher parts count. This work proposes a new fault-tolerant structure for the ANPC IGBT-based converter, using standard devices, with very low additional cost and small complexity. The main goal is to show that the ANPC converter can overcome different and successive failures in its power devices without loss of functionality, before its definitive downtime.