Hierarchical Dispatch of Multi-terminal HVDC Transmission System Considering Flexibility Retrofits of Sending-end Thermal Power Units

The high voltage direct current (HVDC) system has become an important means for pooling widely distributed wind power. In this paper, the flexibility retrofits of thermal power units that directly support local voltage source converter (VSC) stations are considered to enhance the grid integration of wind power and the operating economics of the HVDC system. The flexibility retrofit measures for thermal power include the application of high-power plasma ignition burners and the single-mill operation. The designed multi-terminal HVDC network is weakly connected with the sending-end high voltage alternating current (HVAC) grid. A hierarchical scheduling structure is presented to decompose the scheduling problem of the hybrid AC/DC system into three interactive levels, which can be solved by utilizing the analytical target cascading (ATC) method. Simulation studies indicate that the flexible operation of thermal power has been greatly improved so that the wind power supporting VSC stations can be better accommodated.