Fault-Tolerant Methods for Three-Level T-Type Inverter to Balance Neutral-Point Voltage

This paper proposes new fault-tolerant (FT) space-vector modulation (SVM) techniques for three-level T-type inverter (3L-T2I) to balance neutral-point voltage (NPV) under faulty conditions. Unlike conventional FT-SVM methods, which use three-nearest vectors to synthesize output voltages, the proposed SVM methods add one small vector to conventional switching sequences to obtain NPV balance. Dwell-time of extra vectors are maximized to decrease NPV balanced time. Comparing to conventional FT-SVM methods, the proposed approaches can significantly reduce the difference in capacitor voltages. As a result, the amplitudes of DC component and high-order harmonics of output currents are also reduced. Consequently, the quality of output current is improved. Experimental results, which are conducted by a 1.1-kVA laboratory prototype, are presented to verify the effectiveness of the proposed FT methods. Comparison studies based on experimental results are also presented to demonstrate the advantages of NPV balance of the proposed method compared to conventional FT methods.