A Robust Open-Circuit Fault Diagnosis Method for Three-Level T-Type Inverters Based on Phase Voltage Vector Residual Under Modulation Mode Switching

This article proposes a new phase voltage vector residual-based fault diagnosis method to distinguish the similar open-circuit (OC) fault features of different switches in the three-level T-type inverter. The fault feature based on phase voltage residual can be generated with the designed expected phase voltage model considering different modulation strategies and modes. Under the zero-crossing (ZC) and non-ZC conditions of the faulty phase, the voltage vector residual characteristics caused by OC faults can be summarized. An adaptive residual vector amplitude threshold is designed based on uncertainty propagation using parameter error, dead time, and delay time as system error inputs. In addition, a hierarchical fault diagnosis scheme is proposed, which involves two steps. First, the group-level fault can be located according to voltage residual vector amplitude and angle. Next, the three-level modulation mode of all phase legs is switched to the two-level mode to further identify the faulty switch from the faulty group. The proposed method can achieve a reasonable balance between robustness and rapidity. Meanwhile, complexity and adaptability are also considered. Experimental results under various conditions sufficiently verify the robustness and effectiveness of the proposed fault diagnosis method.