Advanced Control of Wind Turbines connected to MMC-MTDC without Offshore DC Breaker

Multi-terminal high-voltage-direct-current based on modular-multilevel-converter (MMC-MTDC) is a proposing solution for the offshore wind power transmission. This paper investigates the operation of MTDC when the offshore AC breaker and DC switches are used to deal with the DC fault for the offshore side. An advanced control for the offshore wind turbine converters and MMC in the MTDC system, which achieves seamless transition between the grid-following mode and grid-forming mode without switching PLL, is proposed. The effectiveness of the proposed control is validated by PSCAD/EMTDC simulations. The results show that the offshore wind turbine converter and MMC can maintain stable operation after the fault and during the fault recovery.