A novel DC charging strategy for modular multilevel converter in a HVDC system

The pre-charge process is one crucial step of the operating for modular multilevel converters. Improper charging strategy may damage sub-modules due to capacitor voltage unbalance, or cause tripping operation of the whole system due to leg current overflowing. Thus, it is important to analyze the charging strategy and charging current suppressing method before designing the controller of modular multilevel converter. In this work, a novel DC-link charging strategy is proposed. Experiments results have been demonstrated to verify the validity of the proposed strategy.