Backstepping DC Voltage Control in a Multi-terminal HVDC System Connecting Offshore Wind Farms

Wind power is projected to play an important role in the current and future power systems. To integrate offshore wind farms to the existing onshore grid, voltage source converters (VSCs) based high voltage direct current (HVDC) transmission have drawn considerable interests from researchers and industries. As the most important variable in a DC system, DC voltage indicates the power balance between different terminals thus must be maintained in a safe range. To distribute transmitted wind power among distinct onshore AC grids, different operation modes need to be considered. This paper proposes to interoperate the backstepping DC voltage control method between various operation modes. DC cable dynamics are included in the DC voltage controller design to eliminate the effect of DC transmission line. Simulation is carried out in Matlab/Simulink to verify the backstepping enhanced DC voltage control method. It is shown that the transient stability can be improved with the backstepping method.