This paper proposes a novel dc power-flow controller for a multiterminal HVDC system, which can be inserted in series on transmission lines to manage the dc power flow. Its key features include: 1) simpler circuit topology; 2) fewer components; and 3) the elimination of an external power supply and low-frequency high-voltage-insulation isolated transformer. A three-terminal HVDC system, including the dc power-flow controller, is studied and its operation principle and characteristics are analyzed. A simulation mode is built to test the feasibility and effectiveness of the proposed dc power-flow controller with cases of power injection step down, power loss of one terminal, and power-flow reversal. A three-terminal dc system is built in the lab to validate the dc power-flow controller. The results show that the proposed dc power-flow controller can enhance the performance and controllability of a multiterminal HVDC system.