Analysis of a Series-Parallel-Connected Type DC Power Flow Controller in Multiterminal Grids

In multiterminal or meshed dc grids, power flow of each line cannot be fully controlled via converter stations. The dc power flow controller (DCPFC) is, therefore, used to solve such problem. This article presents a series-parallel-connected type DCPFC for multiterminal or meshed dc grids. The topology consists of three functional blocks based on power electronics circuits: Parallel tapping block, power transfer block, and series tapping block. By tapping a small fraction of power from a dc terminal and distributing that power back to any dc line, the proposed series-parallel-connected type DCPFC achieves a decoupled control for line power flow over a full rated range. Meanwhile, the proposed topology combines the feature of expandable architecture in the series-connected type interline DCPFC with the advantage of independent flexible power regulation range from the parallel-connected type DCPFC. The operation principle and the control strategy of the proposed DCPFC are demonstrated in detail. Simulation models built in MATLAB/Simulink and downscaled experimental setup are used to validate the operation principle and theoretical analysis of the proposed DCPFC.