Control strategy of system coordination in Nanao multi-terminal VSC-HVDC project for wind integration

The ±160 kV three-terminal voltage source converter (VSC) based HVDC system under construction in Island of Nanao, China, is expected to be the first multi-terminal VSC-HVDC industrial project. The system has been designed to extract wind energy from the wind intensive areas on the island to the bulk power system at the mainland of China. At present, the system is being tested online, and planned to be committed by the end of 2013. Due to the outstanding controllability of VSC-HVDC system, the control strategy becomes critical for coordination between each converter station, as well as the interconnected DC and AC system. This paper presents the detailed control schemes for each individual active and reactive power parameter according to different operation modes, including paralleled operation of AC and DC circuits, DC operation only, and working as a reactive power compensator. In this system, the power flow management ensures efficient power transmission in normal operation, and fast response in emergency condition, which improves the ability of fault ride-through. Also, the converter station is capable to provide a stable AC system for connecting wind farms.