Detection Method for Open-Circuit Fault in Neutral-Point-Clamped Inverter Systems

This paper presents a fault detection method for open-circuit faults of a switching device in neutral-point-clamped inverter systems, which is based on the inherent characteristic of continuous pulsewidth modulation. The proposed method is achieved by measuring the pole voltage and its duration time. The pole voltage includes information of switching states in the inverter system but not affected by the load. Therefore, a fault condition of the inverter system itself can be diagnosed through analysis of pole voltage. Compared to conventional fault detection methods, the proposed fault detection method has faster detection capability that is within two sampling times and is much simpler to implement. Therefore, the use of the proposed method could minimize harmful effects such as imbalance of dc-link voltage and overstress on other switching devices. The validity of the proposed fault detection method is verified through experimental results.