A converter device comprising a converter and a coil arrangement that contains a number of coils. The coil arrangement has a plurality of interconnected coils. Toroidal cores of a soft magnetic nanocrystalline material are associated with each of said coils. A coupling toroidal core (11) is provided with a core opening (12) through which at least two windings (8, 9) of different coils can be guided and mounted. At least the winding of one coil is guided and mounted through a core opening of an individual toroidal core (13, 14). An open/closed-loop control device is provided with a current controller that acts on the coils such that direct current components are compensated by currents flowing through the windings of the coils.