The Tolerance Control Method Based on Zero-Sequence Circulating Current Suppression for Parallel T-Type Three-Level Rectifiers

Zero-sequence circulating current (ZSCC) suppression and fault-tolerant control (FTC) are important guarantees for the safe and reliable operation of parallel T-type three-level rectifiers (PT(2)3LRs). However, none of the existing literature can solve the FTC under the ZSCC suppression of the PT(2)3LRs when the open switch fault (OSF) occurs in neutral-point (NP) switches. In order to solve these issues, a novel FTC method based on ZSCC suppression is proposed in this article. First, an improved finite-time controller is constructed to suppress the ZSCC by adjusting the difference of zero-sequence duty ratio between two rectifiers, completely. Then, based on the principle of area equivalence, the switching sequence is reconstructed by changing the state switching mode of the fault phase in real-time. As a result, the FTC under the OSF of NP switches is realized without affecting the suppression of ZSCC. Compared with the existing methods, the proposed method not only realizes the suppression of the ZSCC of the PT(2)3LRs but also completes the FTC under the OSF of NP switches, which guarantees the ZSCC suppression ability under the OSF of NP switches. Consequently, the power quality of the ac side of the PT(2)3LRs is improved significantly during the normal operation and the operation under the OSF of NP switches. Thus, the safe and reliable operation of the PT(2)3LRs is guaranteed effectively. Finally, the feasibility and correctness of the proposed method are verified by experiment results.