The subject matter of this thesis report investigates a synthetic inertia and dynamic stability technique for grid inter-connection of large VSC-HVDC connected offshore windfarms. Assuming traditional load frequency control on the AC grid for the short-term reallocation of power generation resources due to load disturbances, this technique ties the dynamic response of the windfarm to the dynamic response of a small synchronous generator at a point of common coupling. The report uses electromagnetic transient simulation to show that the windfarm can be made to react to onshore frequency events similar to any other synchronous generation source participating in power-frequency regulation. Simulation is also used to show that the windfarm can actively contribute to the frequency stability of the onshore AC grid.