To reduce CO2 emissions produced by electricity generation, conventional fossil fuel power plants are being decommissioned. Renewable energy sources (RES) and interconnectors are replacing these old power plants but have different operating characteristics. A key concern as the conventional fossil fuel power plants are displaced is the reduction in system inertia. A reduction in system inertia will require faster control schemes to be implemented to prevent frequency and rate of change of frequency (ROCOF) limits from being exceeded. Frequency response schemes that can emulate inertia, often called synthetic inertia, are required and this will necessitate the need for fast controlled devices. VSC-HVDC is a desirable interface option for the power levels and controllability required to provide synthetic inertia. This paper reviews supplementary frequency control schemes applied to VSC-HVDC and co-ordinated control strategies applicable to HVDC connected systems and islanded systems.