A coordination control strategy of voltage source converter based MTDC for offshore wind farms

This paper proposes a coordination control strategy of voltage source converter based multi-terminal DC (VSC-MTDC) transmission system for integrating large-scale offshore wind power. Using a typical five-terminal DC transmission system as an example, coordination control strategy based on local controller among converter stations is proposed. Based on the DC voltage-active power characteristic, improved control strategy for auxiliary converter station and APC converter station are proposed respectively. Also the working mode of the two converter stations is analyzed. The basis of parameter selection of auxiliary converter station and APC converter station is presented due to DC power flow distribution and maximum and minimum operational mode. Finally, simulations in PSCAD/EMTDC are conducted to validate the multi-point DC voltage control method under various operating state in normal, master converter station fault and auxiliary converter station fault conditions respectively. Results show that this method can guarantee the active power allocation of VSC-MTDC transmission system and good control effects are obtained.