A multiport power-flow controller for DC transmission grids

This paper proposes an m-port converter structure for high-voltage dc (HVDC) applications to facilitate power-flow routing between k controlled dc buses and m-k independent dc networks. Power-flow control is achieved via the injection of incremental dc voltages between the networks; thus, the converter structure is only rated for a fraction of the rated power and voltage of the connecting dc networks. Unlike previously proposed dc power-flow devices, these incremental dc voltages are generated without requiring power exchange with an external ac network. There are four variants of the structure, each offering unique advantages for deployment. These variants, and the modules that comprise them, are presented. A sample simulation case study is performed to demonstrate three-port bidirectional power-flow control between networks of similar voltage (495/500/505 kV). The proposed converter structure is shown to route power between the networks using modules with megavolt-ampere ratings of approximately 2% of the transmitted power. Thus, the proposed converter structure offers a highly cost-effective means of routing and controlling dc power flows within emerging HVDC grids.