A method for controlling a modular converter, having a plurality of M converter cells, including an active AC-to-DC converter operable in one of a plurality of modes; a DC-to-DC converter; a secondary side of said AC-to-DC converter and a primary side of said DC-to-DC converter connected in parallel with a DC-link capacitor, wherein the primary sides of the converter cells are connected in series, with a first converter cell connected to a line, preferably a medium voltage line, providing an AC line voltage an M-th converter cell connected to a ground; operated by a method placing the converters in bypassed, active or diode mode.