Offshore AC grid management for an AC integrated VSC-HVDC scheme with large WPPs

Point-to-point VSC-HVDC Wind power plant (WPP) links connected offshore by AC cables can be called an AC integrated VSC-HVDC scheme or virtual multi-terminal DC (MTDC) grid. Since, the AC integrated VSC-HVDC scheme forms an offshore AC grid, parallel operation of offshore VSC-HVDC converters is required. This paper compares three offshore converter control topologies: (i) feedforward control of AC voltage and frequency, (ii) feedback control of AC voltage, and (iii) feedback control of AC voltage and frequency with an inner current loop. The performance of power and current based droops has been assessed for the parallel offshore converters. Simulations carried out in DIgSILENT Power Factory are presented to illustrate the effect of these offshore converter control strategies on the dynamics of the AC system following the offshore grid disturbances.