Open-Phase Fault Research on the Parallel-Connected 40-Pulse Rectifier With Multioutput Auto-Connected Phase-Shifting Transformer

To improve the normal operation power quality, the dc side harmonic reduction circuit (HRC) has been extended to the multipulse rectifiers (MPRs) based on five-phase bridge rectifier. The power quality under fault conditions is also an important aspect that affects the overall reliability of the rectifier system. This article is focused on the open-phase fault research on the passive MPRs with autoconnected phase-shifting transformer. The parallel-connected 40-pulse rectifier based on the five-phase bridge rectifier is selected as the main research circuit. Under the primary or secondary side open-phase faults, the operation modes of the main circuit and the HRC are discussed. Based on the waveform information, the relations between the fault characteristics and the fault types are established, which is useful for fault detection. Under the primary side open-phase fault, the current proportions of the two parallel-connected bridge rectifiers are calculated. In comparisons with the 24-pulse rectifier, the quantitative relationship between the increase of phase number and the improvement of fault power quality is clarified. Based on the research methods and conclusions presented in this article, the structure of the MPR can be designed that fulfills the specific power quality standard under fault cases or reserves a certain safety margin to reduce the damage to the rectifier system and the ac grid.