A novel protection scheme for three-level converter based on monitoring flying capacitor voltage

This paper presents a novel protection method for three-level converters. The three-level converter is subject to voltage unbalance, which can result in switch overvoltage and system failure. This abnormal phenomenon can be detected by monitoring the voltage across the flying capacitor (Vcss). Based on simulation analysis, monitoring the Vcss is also an effective way to detect various system faults, including shoot-through. Using the Vcss as the signal for fault detection, the proposed protection scheme can improve the system reliability without any additional components on the power stage and impact on the performance. The protection method can not only protect the system against unbalanced voltage stresses on the switches, but also provide a remedy for the system as faults happen. Furthermore, under/over input voltage lockout can be replaced by the proposed protection scheme. The verification is performed by the experiment with a three-level parallel resonant converter.