A Review of Fault-Tolerant Control Methods for Cascaded H-Bridge Multilevel Inverters

This paper is a comprehensive survey of existing fault-tolerant control methods for the cascaded H-bridge inverter (CHBI) with faulty cells. These methods are widely proposed in the literature to rebalance the CHBI output line-to-line voltages even if its line-to-neutral voltages remain unbalanced due to the failed cells. However, the details of their performances are dispersed across the literature. Hence, the paper discusses a comparative analysis of the most common fault-tolerant control techniques. First, these control approaches are classified according to their operational principle, key features, and limitations. Then, a detailed description of each method is discussed, where analytical expressions of their respective algorithm and implementation scheme are provided. For comparison purposes, extensive simulation results at various operating points are provided for a three-phase, seven-level CHBI topology supplying an induction motor. The comparison performance between the investigated methods is performed based on the magnitude of the common-mode voltage, the maximum achievable balanced line-to-line voltage, the current unbalanced ratio, as well as their total harmonic distortion values at various operating points.