The Zero-Sequence Circulating Current Suppression Method for Parallel Three-Level Rectifiers System Under the Open-Circuit Fault of Neutral-Point Switches

In parallel T-type three-level rectifiers system (PT
²
3LRs), when the open-circuit fault (OCF) of neutral-point (NP) switches occurs, the existing zero-sequence circulating current (ZSCC) suppression methods are not capable of suppressing the ZSCC any more since the ZSCC model of PT
²
3LRs is changed. Significantly, the ZSCC suppression issue of PT
²
3LRs under the OCF of NP switches has not been researched in previous literatures. To overcome this limitation, a novel ZSCC suppression method for PT
²
3LRs with the OCF of NP switches is proposed. First of all, according to the principle of area equivalence, the fault-tolerant control (FTC) is accomplished by reconstructing the switching sequence. Second, a novel ZSCC model with FTC is established. Then, according to the novel ZSCC model, the ZSCC control method based on “PI + feedforward” is proposed. This method is realized by modifying the turn-
on
time of three-phase of fault rectifier in PT
²
3LRs. Consequently, the method proposed in this article effectively restrains the ZSCC of PT
²
3LRs with the OCF of NP switches. Finally, the simulation and experiment results verified the correctness of proposed method.