Comparison of tolerance controls for open-switch fault in a grid-connected T-type rectifier

Multilevel rectifier topologies are commonly used in wide-power range applications. The T-type rectifier topology, which is a three-level topology, has an advantage in terms of efficiency compared to a neutral-point clamped (NPC)-type topology. In applications using the T-type rectifier topology, improving reliability has gained increased attention recently. A tolerance control for T-type rectifiers is necessary to improve the reliability of applications. When an open fault of switches connected to the neutral-point occurs, the NPC-type rectifier cannot restore distorted input currents, on the other hand, the T-type rectifier can eliminate the input current distortion completely. In this paper, we report two studies: 1) a three-level switching-oriented tolerance control, which is advantageous in terms of efficiency, for the S_x2 and S_x3 open-switch faults of the T-type rectifier and 2) comparison of the proposed tolerance control with two existing tolerance controls. In particular, the current total harmonic distortion, dc-link voltage ripple, and switch losses of these tolerance controls are analyzed by using simulation and experimental results.