This paper compares damping-improvement results of a series static synchronous compensator (SSSC) and a series vectorial compensator (SVeC) on an offshore wind farm (OWF) connected to a power system with a synchronous generator. The aggregated model of a permanent-magnet synchronous generator (PMSG) with its power converters is used as the studied OWF of 80 MW. To clear compare the damping contributed by the two flexible AC transmission systems (FACTS) devices, frequency-domain approach based on root-loci analysis is carried out. Time-domain approach based on nonlinear model simulations under disturbance conditions is also performed. It can be concluded from the simulation results that the SVeC can offer better damping characteristics to both mechanical mode and exciter mode of the studied SG-based power under various operating conditions and a disturbance condition than the SSSC.