<p>Multilevel inverters are prospective in high-voltage and high-power applications because of their low harmonics and high efficiency. Open-circuit faults are a critical factor affecting the reliability of power electronic devices. It is essential to locate faults fast and accurately to ensure the stable operation of multilevel inverter systems. Switching devices in diagonal positions have similar output characteristics under fault conditions, making it difficult to discriminate the fault switch effectively. Thus, a four-state reverse current active fault diagnosis is proposed in this paper. The carrier arrangement sequence is reconstructed after the fault is detected, avoiding the similarity of fault characteristics. The fault is located by logical judgment based on the current state of the carrier arrangement and the direction of the output current when reverse current is detected. Good real-time performance and strong robustness, along with low computational complexity, are achieved by the proposed method. The experimental results were obtained using a five-level cascaded H-bridge multilevel inverter topology. The effectiveness of the proposed fault diagnosis method is validated by the experimental results.</p>