Tolerance controls for open-switch fault in a grid-connected T-type rectifier at low modulation index

Multi-level rectifier topologies are widely used in applications of the wide-power range. T-type topology, which is one of many three-level topologies, has an advantage in terms of an efficiency compared to a neutral-point clamped (NPC)-type. In applications using T-type rectifier topology, the interest in reliability has been increased recently. Therefore, a tolerance control for T-type rectifiers is necessary to improve reliability of applications. When an open-switch fault of switches connected to the neutral-point occurs, the NPC-type rectifier cannot restore distorted input currents; however, the T-type rectifier is able to eliminate input current distortion completely. In this paper, two tolerance controls for the T-type rectifier at low modulation index are proposed and their characteristics are analyzed. The effectiveness and performance of two proposed tolerance controls are verified by simulations results.