METHOD FOR ENERGIZING A MODULAR MULTILEVEL CONVERTER

The present disclosure relates to a method for energizing a modular multilevel converter (100) comprising converter valves (101), each converter valve having a plurality of interconnected cells (102), wherein each cell comprises a plurality of power electronic switches (105, 106, 107, 108) in a full-bridge arrangement, a chargeable element (109), and a plurality of gate drive units (118), one gate drive unit for each power electronic switch. The method includes:providing power to the modular multilevel converter from an external power supply (S201);powering the cells, thereby charging the chargeable elements of the cells (S202);generating, when a cell voltage caused by said charging exceeds a first threshold voltage level, a cell sub-ready signal for that cell (S203);generating, when at least a predetermined minimum number of cells have generated the sub-ready signal, a sub-ready_for_operation signal (S204); andrunning a deblocking sequence comprising closing a first power electronic switch (105) in all cells to electrically configure the cells to be continuously charged as a half-bridge cells, and keep the first power electronic switch closed until the cell voltage has reached a converter operable voltage, which is higher than a second threshold voltage (S205).