Matrix-Based Approach for Open-Circuit Fault-Tolerant Analysis and PWM Design of Active Neutral-Point-Clamped Converters

Active neutral-point-clamped converter adds open-circuit fault-tolerant (OCFT) capability compared with the widely used original neutral-point-clamped (NPC) topology. However, such capability is hard to utilize due to difficulties in pulse-width modulation (PWM) design and the randomness of failure points, particularly in high-level converters. Current research mainly focused on low-level topologies with a limited number of fault scenarios; moreover, the analysis and design are performed in a nonsystematic way. In this article, the OCFT operations of active NPC (ANPC) converters with multiple fault switches are investigated and the systematic PWM design process is proposed. First, different matrices are proposed for the ANPC converters to capture the complicated topology information and achieve an exhaustive analysis of the topological redundancy. Then, a step-by-step process is proposed to derive the suitable OCFT PWM patterns. The five-level ANPC converter is investigated as an example. Its experimental results validate that the proposed approach can 1) properly predict the behavior of converters systematically so that the tolerable faults and intolerable can be identified during the design procedure, and 2) the inherent fault-tolerant capability of the five-level ANPC converter can be guaranteed through the proposed method, and 3) multiswitch open-circuit faults can be easily dealt with by implementing suitable carrier-based PWM schemes.