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 (PT23LRs), 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 PT23LRs is changed. Significantly, the ZSCC suppression issue of PT23LRs under the OCF of NP switches has not been researched in previous literatures. To overcome this limitation, a novel ZSCC suppression method for PT23LRs 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 PT23LRs. Consequently, the method proposed in this article effectively restrains the ZSCC of PT23LRs with the OCF of NP switches. Finally, the simulation and experiment results verified the correctness of proposed method.