The invention relates to a device for converting voltage comprising a converter and a controller, wherein the converter has three half bridges, each with four transistors, and at least one half bridge has two switching elements, wherein by means of a first switching element, a central tap between two diodes is connected in a first switched position to a neutral point of a DC link capacitor and, in a second switched position, to a positive charging connection for an external DC voltage source, and by means of a second switching element, a central tap of the half bridge is connected in a first switched position to a pole of an AC voltage connection, and in a second switched position to a negative pole of a DC voltage connection. Moreover, the invention relates to a traction network as well as a method for charging a battery of a traction network by means of an external DC voltage source.