The invention relates to a converter device comprising a converter and a coil arrangement that contains a number of coils, wherein the coil arrangement has a plurality of interconnected coils, and toroidal cores consisting of a soft magnetic nanocrystalline material are associated with each of said coils, a coupling toroidal core (11) being provided with a core opening (12) through which at leasttwo windings (8, 9) of different coils can be guided and mounted, at least the winding of one coil being guided and mounted through a core opening of an individual toroidal core (13, 14), and an open/closed-loop control device being 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.