Power flow controllers (PFCs) might be needed in highly meshed High-voltage direct current (HVDC) systems to redistribute the current and power in the various cables. This paper introduces two new unidirectional topologies, which are among the most simple PFC topologies. It describes the working principle, electrical characteristics, various fault cases, and the corresponding protection circuits in detail. Experiments have been conducted on a scaled-down prototype to verify the full-scale HVDC system simulations. Discussion and extension of the PFC with more than two transmission lines are provided.