A Unified Fast Open-Circuit Fault Diagnosis Method for 3L-NPC Power Converters

Fast and accurate diagnosis is essential to fault ride-through and reliability enhancement of power conversion systems. For three-level neutral-point-clamped (3L-NPC) power converters, most diagnosis methods fail in distinguishing faulty IGBTs and diodes. Here, we propose a unified fast open-circuit fault diagnosis technique for all power devices in a 3L-NPC converter. The proposal is realized simply in two steps via the classical “quasi-power” (QP) concept of Tellegen's theorem. First, the faulty outer IGBTs and freewheeling diodes will be allocated with one sampling period solely via comparing the QP values. Afterwards, a voltage signal will be injected via manipulating the IGBT gate signals in a direct predictive control frame, and the correspondent QP value will be recalculated to distinguish and allocate the faults between an inner IGBT and a clamping diode, with one additional sampling period. Since the QP depends solely on the topological and switching state of power converters, the proposal hence immunes to both parameter and operation condition variations. Finally, both signal hardware-in-the-loop and power circuit experimental data validate the effectiveness of the proposed method at different operation scenarios.