Multiport High-Power LCL DC Hub for Use in DC Transmission Grids

This paper proposes an LCL dc hub concept which plays the role of a dc substation in a dc grid. The hub is capable of connecting multiple dc transmission lines with different dc voltages. Each dc transmission line can be added to or isolated from the hub without affecting the operation of the other dc transmission lines. The hub is based on multiple ac/dc insulated-gate bipolar transistor-based converters and an internal passive LCL circuit without internal ac transformers. The LCL circuit is designed to interconnect multiple ac/dc bridges with different dc voltages and achieving minimal reactive power circulation at each converter bridge. Each ac/dc bridge controls its active power independently. The designed hub has the ability to ride through the dc faults by keeping the fault current within the order of its rated value. Detailed PSCAD/EMTDC simulations of a seven-port test system are presented to validate the proposed topology.