Power Shifting Strategy Based on Extended Operation Region for VSC-MTDC System Integrated with Offshore Wind Farms

Multi-terminal voltage source converter-based high voltage direct current (VSC-MTDC) technology has become an efficient solution for grid integration of large-scale and long-distance offshore wind power. When onshore grid power fluctuations elevate the DC voltage of VSC-MTDC system, the surplus power causing the DC overvoltage issue can be effectively transferred through the power shifting method. To enhance the power shifting capability of receiving-end converters (RECs) and mitigate DC overvoltage, this paper proposes a coordinated power shifting strategy for VSC-MTDC based on the extended operation region. Firstly, the topology and control model of the VSC-MTDC system integrating offshore wind farms is established. Secondly, considering constraints containing apparent power, AC bus voltage, AC current, and voltage modulation ratio, the extended operation region model with regard to the overload capacity of REC is constructed. Furthermore, the coordinated active power shifting strategy for multiple converters is proposed to cope with onshore grid power fluctuations. Finally, simulation models of three-terminal and six-terminal VSC-MTDC systems are built using PSCAD V5 software. Simulation results show that the proposed strategy can exploit the system’s operational flexibility and reduce the risk of DC overvoltage, thus enhancing the disturbance immunity of VSC-MTDC system against onshore grid fluctuations.