Single-switch open-circuit diagnosis method based on 3D vector shift for T-type three-level inverters

Abstract

Fault diagnosis plays a significant role in improving the reliability of T-type three-level inverters. Therefore, a method for diagnosing the IGBT open-circuit faults of T-type three-level inverters based on vector 3D offset is proposed in this paper. The characteristics of the voltage vector shift in single-switch open-circuit faults under three-dimensions are analyzed. In the first dimension, the fault phase was identified by the different offset of three-phase voltage vectors at the polar coordinates. In the second dimension, the output voltage vectors were mapped to the common-mode voltage level in space, and faulty bridge arms were identified by the transition direction of the common-mode voltage. In the third dimension, the specific faulty transistor within a set of bridge arms was identified by the voltage difference between the upper and lower capacitors on the DC side, which was caused by the regional shift of the voltage vectors in the plane. Experimental results show that the proposed method can effectively diagnose the OC faults of 12 switches in T-type three-level inverters. The key advantages of the proposed method are its capability to significantly enhance fault diagnosis speed, bolster diagnostic robustness, and remain impervious to variations in load and modulation coefficients. Moreover, it eliminates the need for additional sampling circuits.