Reconfigurable multiphase multi GW LCL DC hub with high security and redundancy

Future DC transmission grids may include a central DC hub which will be connecting numerous DC lines and transferring multi GW power. The LCL DC hub is a multipart high power DC/DC converter that incorporates an inner LCL circuit to interconnect DC systems with different DC voltages through DC/AC ports. The LCL DC hub has an intrinsic attribute to limit the propagation of DC faults such that DC fault at one DC transmission line will not bring down the DC voltage or cause DC over current on other DC lines. As the operating security of the hub is of top concern, this paper proposes a reconfigurable multiphase method to avoid a common failure mode. The n-1 redundancy and expandability using multi-phase approach are analyzed and compared with other methods. A fast, on-line phase reconfiguration and phase replacing control of the DC hub are proposed and verified, enabling the hub to continue operating under single-phase faults. Common mode current of the LCL DC hub is analyzed to provide guidelines on structure and operation of the ports. It is concluded that 4-phase topology, possibly with a redundant 5th phase might offer best overall performance and with high redundancy/security required for large DC grids. (C) 2014 Elsevier B.V. All rights reserved.