Nanao multi-terminal VSC-HVDC project for integrating large-scale wind generation

Due to the renewable generation target and the continuously increasing electrical demand, a large number of wind farms are being planned in China. Meanwhile, the corresponding transmission infrastructures have to be developed to facilitate the increased renewable penetration. HVAC, conventional HVDC and voltage source converter (VSC) based HVDC are possible options for building new lines. Compared to the other approaches, VSC-HVDC offers better transmission efficiency, flexible and independent power control, reactive power compensation, and unlimited terminal configurations. Therefore, a multi-terminal VSC-HVDC system is being constructed to extract wind generation from Island of Nanao to the mainland of China. This paper presents a comprehensive architecture of the transmission network, as well as the corresponding control system. As a key factor of running a multi-terminal HVDC system, the system coordinated control has been investigated to cooperate with the system start-up and shutdown processes. In addition, the control strategy of online re-commissioning of a station after maintenance has been designed for this project, using disconnectors instead of DC circuit breakers.