Power-Sharing in a Meshed HVDC Network and Its Application for Frequency Support

In recent years, the High Voltage Direct Current transmission (HVDC), especially the Voltage Source Converter (VSC)-based HVDC, has been considered as a promising technology to convey power from offshore wind farms to onshore Alternating Current (AC) grids. By connecting many wind farms via a meshed HVDC, the total variation of wind power output would be reduced due to the increase in geographical distribution of wind farms. A meshed HVDC transmission also forms a future cross-border system where a DC network connects many AC grids and wind farms. In such a structure, the power reserve can be exchanged between all AC grids. In the power system with a high penetration of wind power, it is considered as a good method to strengthen the frequency security, and reduce the reserve amount. Several power-sharing methods have been proposed for meshed HVDC networks. Each strategy has its own advantages and disadvantages. This paper aims to investigate the feasible control strategies that allow power sharing among terminals in a meshed HVDC. A simulation model with a six-terminal meshed HVDC system is established by PSCAD/EMTDC software. By performing various operating scenarios, the comparative results demonstrate the features of each control method on power-sharing to strengthen AC grids.