Optimal Droop Control ofmulti-terminal VSC-HVDCgrids

High-voltage direct current (HVDC) networks connecting offshore wind power plants to land AC grids exhibit different characteristics, and in particular they offer new control alternatives. In wind power applications, an HVDC transmission results in a multi-terminal direct current (MTDC) network in which its terminals are connected to voltage source converters (VSCs). These converters permit the transfer of power from wind farms to AC grids where the loads are connected. The aim of droop control in these MTDC networks is to ensure a proper power transmission, which implies to maintain the DC voltage almost constant and also to attenuate the effects of changes in the incoming power and faults in the AC grids. Multi-terminal VSC-HVDC networks in the context of wind farms integration exhibits a time-varying behavior as a consequence of changes in the operation conditions. To describe this behavior, a general time-varying description of multi-terminal VSC-HVDC networks has been introduced.