Open-circuit Fault Diagnosis Method for Grid-tied T-type Converters based on Harr-like Features

The grid-tied T-type converter can work in the rectifier state and the inverter state. The open-circuit fault diagnosis under the two conditions faces the challenge of fault detection and fault location, respectively. An open-circuit fault diagnosis method for grid-tied T-type converters based on Harr-like features is proposed in this paper, considering both rectifier and inverter states. The Harr-like features are a set containing two-rectangle features (2RF) at different scales and three-rectangle features (3RF). The diagnosis is a step-by-step process. At first, a small-scale 2RF is used to represent the weak fault information. In addition, the fault is enhanced and detected by the average magnitude difference function (AMDF). In the fault phase location, the Pearson correlation coefficients of the three-phase currents are calculated with a period-scale 2RF. The coefficients are also used to distinguish between the outer transistor fault and the inner transistor fault in the rectifier state. When the former is obtained, the fault transistor is located according to the features at the first step. For the other condition, the fault transistor is located by the features extracted from a period-scale 2RF and a three-half period-scale 3RF. Only the three-phase current signals are needed, without other signals and parameters. The experimental results verify the effectiveness of the proposed diagnosis method.