An Overview on the Recent Advances of the Voltage Source Converter Control Modes in Terms of their Roles in Transmission Grid Ancillary Services

Voltage Source Converters (VSC) are expected to be one of the major actors in future AC transmission grids. Their role includes the interconnection of renewable energy, from distributed sources such as residential PV to large Offshore Wind Farms (OWF) using HVDC. With the ongoing decommissioning of traditional power plants with their synchronous generators, VSCs must now bring support functions to the grid. The aim of this paper is to review the different grid services that can be achieved through VSCs and discuss their compatibility with the state-of-the-art VSC controls especially the so-called grid-following and grid-forming controls. After presenting the upcoming issues of future grids and classifying the main VSC controls, this paper deals with the different additional control laws which make it possible to support the AC grid. Some recommendations regarding future grid services classifications and power and energy requirements are given. A comparative table is also proposed to assess the role of the different control modes.