M2C-based MTDC system for handling of power fluctuations from offshore wind farms

In this paper a modular multilevel converter (M2C) based multi-terminal direct current (MTDC) system is proposed for the connection of offshore wind farms. Each M2C is modelled with 36 sub-modules per arm with a total of 216 sub-modules consisting of half bridges. An open-loop converter control method is employed for the M2Cs. Power-synchronization control is used instead of a phase-locked loop (PLL) for synchronization. A voltage controller is implemented with power-synchronization control as an inner loop. By means of numerical simulations in PSCAD, it is shown that the system is self stabilizing both at steady state and following power fluctuations of the wind farm.