Open-Circuit Fault Diagnosis Method for Grid-Connected Bidirectional T-Type Converter Based on Geometrical Similarity Measurement

Abstract

Grid-connected bidirectional T-type converter (GBTC) is widely used in power generation, vehicle-to-grid, and other applications because of its bidirectional energy flow and superior performance. However, transistor open-circuit fault can cause serious output harmonics and even system outage. In this work, a novel open-circuit fault diagnosis method is proposed based on geometrical similarity measurement, which is suitable for the rectifier state and inverter state of the GBTC. Under healthy and faulty conditions, current paths and distortions are deeply analyzed. To evaluate the distortions, reference geometry vectors and current geometry vectors constructed from the grid angle and normalized currents are studied. Geometry features including vector triangle area, structural similarity, and contour similarity are used to measure the similarities among the vectors and carry out fault detection, fault phase location, and fault transistor location, respectively. Reasonable diagnostic thresholds are designed, and no additional sensor is needed. The robustness and effectiveness of the method are verified by experiment results.