The DC power flow controller can effectively improve the control degree of freedom of power flows in looped DC grids to help solve the problem of uncontrollable power flow in some DC lines. In light of the limitations of existing DC power flow controllers in actual applications

a new topology of DC power flow controller is proposed to regulate the power flow by managing power exchange between the transmission lines. And its working principle and operation characteristics are analyzed. A general control strategy based on pulse-width modulation(PWM)is designed for various kinds of running state of this topology. With one of the working states as an example

the relations between different state variables are researched. Finally

an equivalent model for a three-terminal DC grid is developed in the electro-magnetic transient simulation soft. The simulation results have verified the feasibility and effectiveness of the proposed topology and control strategy of the DC power flow controller. This work is supported by National Natural Science Foundation of China(No. 51607171).