(1. State Key Laboratory of Advanced Electromagnetic Engineering and Technology (Huazhong University of Science and Technology)， Wuhan 430074， China;2. State Grid Liaoning Electric Power Co. Ltd., Shengyang 110006， China)

A six-terminal voltage source converter (VSC) based HVDC (VSC-HVDC) system is proposed for connecting large wind farms to the main AC grid. A coordinated system control scheme is also presented, i.e., the sending side VSC is AC voltage controlled while the receiving side VSC is DC voltage droop controlled. It can ensure smooth system operation and proper power sharing among different receiving end grids. Simulation results using PSCAD/EMTDC demonstrate its satisfactory performance and flexible operation of the proposed VSC-HVDC system and control strategy under different conditions, including start-up, wind power variation, AC grid short circuit fault and large disturbances caused by the trip of one sending side VSC or one receiving side VSC. This work is supported by the Funds for International Cooperation and Exchange of the National Natural Science Foundation of China (No. 51261130484), National High Technology Research and Development Program of China (863 Program) (No. 2011AA05A112) and State Grid Corporation of China (No. 2013-304).