Method for energizing a modular multilevel converter

A modular multilevel converter comprising converter valves, each converter valve having a plurality of interconnected cells, wherein each cell comprises a plurality of power electronic switches in a full-bridge arrangement, a chargeable element, and a plurality of gate drive units, one gate drive unit for each power electronic switch, the modular multilevel converter being configured to, at an initial power up, receive power from an external power supply and power the cells, thereby charging the chargeable elements of the cells;

• wherein each cell is configured to, when a cell voltage caused by said charging exceeds a first threshold voltage level, generate a cell sub-ready signal;
• and
• wherein the modular multilevel converter is configured to, when at least a predetermined minimum number of cells have generated the sub-ready signal, run a deblocking sequence comprising closing a first power electronic switch 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, wherein each cell comprises control logic configured to, at the beginning of the initial power up, merely provide power to a first gate drive unit of said plurality of gate drive units of each cell, the first gate drive unit being connected with the first power electronic switch, and, when the second threshold voltage has been reached, provide power to the rest of the gate drive units in each cell.