Abstract: A Sengimir rolling mill in the silicon steel department uses GE's MV7309 medium voltage inverter as the main drive. Since it was put into operation, the inverter has had several trip accidents caused by the difference between the positive and negative voltages on the DC side of the inverter of the right winder greater than the threshold, which affected the production efficiency. Starting from the NPP type topology and DC voltage regulation mode adopted by the inverter, this paper analyzed and gradually investigated the various causes that may cause the positive and negative voltage imbalance on the DC side, and completely solved the fault of DC positive and negative voltage imbalance of the right coiling inverter. The treatment of similar faults has strong reference significance.

Key words: Sengimir rolling mill, MV7000, three-level converter, DC link, voltage imbalance