Modular traction converter system with energy storage device for providing a dc link voltage and method for its operation

The circuit device (60) has direct current (DC)-side power converter (61) that is configured such that bi-directional power flow is enabled between direct current (DC) link capacitor and memory device. A direct voltage side of DC-side power converter is connected to capacitor, while alternating-voltage side is connected to primary coil (L1) of transformer (62). A capacitance of capacitive element is selected as function of leakage inductances so that switching of zero voltage and/or zero current is carried out in switching elements (72-75) of DC-side power converter. An independent claim is included for a method for operating circuit device for setting charging state of traction system in electrically driven vehicle.