Estimation and Analysis of NPC and Hybrid NPC Power Converters Reliability

Abstract

This paper proposes a methodology to estimate the reliability of multilevel power converters and applies this methodology to two interesting structures: The first is the conventional three-level NPC (Neutral Clamped Converter) one. The second is a hybridization of the FC (Flying Capacitors) topology and the NPC one. This versatile FC-NPC topology was proposed mainly to improve the fault tolerance capabilities of the NPC power converter. During normal mode operation, the added fourth FC-based leg contributes to the actively balance the NPC neutral point voltage. When one of power switches of the three NPC legs undergoes a short circuit or an open circuit fault, the FC-based leg guarantees the converter operation under theses fault conditions through a reconfiguration of the power structure and the dedicated converter control. In this paper, an analysis of the influence of the added FC-based leg on the reliability of the hybrid converter is carried out. Thus, the reliability of the hybrid fault tolerant converter is modeled using standard reliability tools [1], FIDES guide [2] and the MIL-HDBK-217-F standard [3]. The precise mathematical modeling and estimation of the two converters reliabilities and failure rates show the effectiveness of the hybrid converter towards reliability increase.