Abstract: A direct current tight coupling is provided for connecting two asynchronous high-voltage three-phase power systems which includes a three-phase full-wave static converter assembly assigned to each of the power systems to be connected, with static converter transformers and controllable semiconductors, which are controlled by a central electronic control unit so that the input-side static converter assembly functions as a rectifier and the output-side static converter assembly as an inverter. The controllable semiconductors of a functional group are mounted atop each other forming identical static converter towers. The towers are connected together at the same pole on the d.c. side and on the three-phase side with the assigned Wye- and Delta-connected secondary sides of the static converter transformers. Each of the full-wave semiconductor subassemblies assigned to the four secondary sides of the static converter transformers form a static converter tower.