Coordinated Operation and Control of VSC Based Multiterminal High Voltage DC Transmission Systems

This paper deals with a multiterminal voltage source converter (VSC)-based high voltage dc transmission system (M-HVDC) connecting offshore wind farms to onshore ac grids. Three M-HVDC configurations studied, each with different control strategies. The voltage-current characteristics of VSCs are presented and VSC converter operation with different output powers from offshore wind farms is assessed. A generalized droop control strategy is mainly used to realize autonomous coordination among converters without the need of communication. Operation of the three configurations with respect to their control system is analyzed through PSCAD/EMTDC simulations and experimentation. Results show control performance during wind power change, eventual permanent VSC disconnection, and change in power demand from the ac grid side converter.