Online Fault Diagnosis Method for Grid-Tied T-Type Inverters Based on Specific Frequency Calculation

The T-type inverter plays an essential role in grid-tied high-performance power generation systems, but its reliability is risky due to the open-circuit fault of transistors. In the grid-tied T-type inverter diagnosis, modulation index regulation has a significant effect on the fault distortion of load currents. An online open-circuit fault diagnosis method is proposed in this article for the grid-tied T-type inverter based on specific frequency calculation, considering the modulation index regulation. At first, variations of the three-phase currents under healthy and faulty conditions are deeply analyzed. Then, the fundamental, dc, and second frequency components of the three-phase currents are extracted by equivalent spectrum calculation to perform fault detection, fault phase location, and fault transistor location. The cost of the calculation is small, and no additional hardware is required. At last, the effectiveness of the proposed method is verified by the experimental results.