Multi-Terminal HVDC Grid for Network Interconnection and Renewable Energy Integration

Voltage source converter based multi-terminal HVDC transmission system (MTDC) technology is proposed for network interconnection and integrating large offshore wind farms over long distance. Coordinated DC grid management using close-loop DC voltage control and DC droop characteristics are proposed, to ensure smooth system operation and proper power sharing among various DC converter stations. Onshore transmission network support using the MTDC system for providing dynamic frequency regulation and power oscillation damping is outlined. Simulations for a four-terminal MTDC system connecting two offshore wind farms to two inter-connected onshore AC networks are presented to demonstrate the robust performance of the proposed system during wind speed and power variations, and large disturbances caused by onshore AC fault. The proposed system achieves accurate DC voltage regulation and power sharing. It also provides significant damping and stability support to the onshore power networks after AC fault