Open-circuit Fault Diagnosis Method for Four-wire T-type Three Level Rectifier

Four-wire T-type three level rectifier (four-wire 3LT(2) R) as a kind of multilevel rectifier topologies has different operation states and modulation strategies, compared with three-wire systems and two-level topologies. Therefore, the fault diagnosis algorithms for the latter cannot be directly applied to the former. In this paper, an open-circuit fault diagnosis method for the four-wire 3LT(2) R systems is presented. By analyzing the operation situation of the system under different switching states and the currents in different directions, the abnormal condition of dc-link capacitive voltages in the case of an open circuit fault of a switch element is explained. Except the voltage imbalance between the upper and lower capacitors and the grid voltage angle, an open-circuit fault diagnosis method doesn't use other features. Simulation results verified the robustness and the effectiveness of the proposed fault detection method.