Open-Switch Fault Diagnosis for Grid-Tied HANPC Converters Using Generalized Voltage Residuals Model and Current Polarity in Flexible Distribution Networks

The diagnosis of open-circuit (OC) faults in power switches is the premise for implementing fault-tolerant control, a critical aspect in ensuring the reliable operation of three-level hybrid active neutral-point-clamped (HANPC) converters in flexible distribution networks. However, existing fault diagnosis methods do not clearly reveal the relationship between the switching-state sequence state and the modulation voltage before and after the fault, which limits their applicability in grid-tied HANPC converters. In this article, a generalized voltage residuals model, taken as the primary diagnostic variable, is proposed for switch OC fault diagnosis in HANPC converters, and the physical meaning is established by introducing the metric of “the variation of the pulse equivalent area”. To distinguish between faulty switches with similar fault characteristics, the neutral current path is reconfigured with a set of rearranged gate sequences. Meanwhile, the auxiliary diagnostic variable, named the current polarity state variable, is developed by means of a sliding window counting algorithm. Additionally, as a case study, a diagnostic criterion for the single-switch fault of HANPC converters is designed by using proposed diagnostic variables. Experimental results are presented to verify the effectiveness of the proposed fault diagnosis method, which achieves accurate faulty switch identification in all tested scenarios within 25 ms.