Improved Finite-Time Control for Circulating Current Suppression of Multiparalleled Rectifiers

Multiparalleled three-level rectifiers (MP3LRs) have the advantages of higher power rating and higher reliability. However, the zero-sequence circulating current (ZSCC) will occur when MP3LRs are connected to a common dc bus, which will distort the grid current and threaten the safe and reliable operation of MP3LRs. Significantly, the ZSCC suppression of the MP3LRs is rarely studied. To overcome the limitation, an improved ZSCC suppression method for MP3LRs is proposed in this article. First, a ZSCC model of the MP3LRs system is established. Second, according to the ZSCC model, the ZSCC controller based on “finite-time control + feedforward” is designed, and the strict theoretical proof of system stability is carried out. Third, this method is realized by using the output of ZSCC controller to modify the three-phase switching time of multiple rectifiers (2nd to $N$ th rectifiers). Consequently, the method proposed in this article can suppress the ZSCC of MP3LRs, completely. Compared with the conventional ZSCC suppression methods, the proposed method has better ZSCC suppression performance and stronger anti-interference capability. Meanwhile, it does not increase any hardware cost. Finally, simulation and experimental results verify the effectiveness of the proposed method.