A DC-to-DC converter assembly includes an inverter having first and second terminals connectable to a power transmission network. The inverter has a modular multilevel converter including a first inverter limb extending between the first and second terminals with first and second inverter limb portions separated by a third terminal. Each inverter limb portion includes at least one rationalized module having first and second sets of series-connected current flow control elements connected in parallel with an energy storage device. The current flow control elements include an active switching element directing current through the energy storage device and a passive current check element limiting current flow to one direction. The current flow control elements and energy storage device provide a voltage source to synthesize an AC voltage at the third terminal. A rectifier is electrically connected to the third terminal and connectable to a second power transmission network.