Power converter assembly with a line-commutated power converter and method for starting up the assembly

A method of starting a converter arrangement, the method comprising:

• providing a converter arrangement having:
• a line-commutated converter having an AC voltage terminal for connection to an AC voltage grid via at least one phase line;
• at least one switching module branch connected in series in the at least one phase line, the at least one switching module branch having a series connection of switching modules with terminals configured to generate bipolar voltages that sum to give a branch voltage;
• a bypass branch connected in parallel with the at least one switching module branch, the bypass branch containing at least one switching device formed with activatable semiconductor switches that are connected in an antiparallel connection;
• blocking the switching modules in the switching branch;
• activating the semiconductor switches in the bypass branch with a predetermined delay;
• and
• commutating a branch current from the switching branch to the bypass branch through the delayed activation of the semiconductor switches.