Operation and coordinated control for a multi-voltage-lelve DC grid with large offshore wind farms integrated

Multi-voltage-level DC transmission technology has been proposed to integrate large offshore wind farms in this paper. The DC/DC converters are needed to interconnect the DC grids with different voltage levels or realize DC power regulation. A DC grid with four DC/DC converters and one DC hub is configured in this paper to integrate and transmit offshore wind power from different regions. The DC/DC converters in DC grid are adopted to control either voltage or power. The topologies and control strategies of DC/DC converters and DC hub are presented. The coordinated control strategies between DC grid and offshore wind farms are proposed under various operation conditions. With the designed operation and coordinated control strategies between DC grid and offshore wind farms, the DC voltages in DC grid can be stabilized; power exchange and control in DC grid can be realized when offshore wind power fluctuated or changed. Simulation results carried out by PSCAD/EMTDC software tool prove the effectiveness of the presented topology and the coordinated control strategies for DC grid operation. It has also provided the possibility to implement the interconnection between DC grids with different voltage levels to form multi-voltage-level DC grid in the future.