Frequency support among asynchronous AC systems through VSCs emulating power plants

This paper proposes a new control scheme for the Voltage Source Converters (VSCs) of a High Voltage Direct Current (HVDC) grid connecting asynchronous AC systems, so that the latter can mutually support their frequencies after a disturbance. The scheme involves no communication between VSCs. It is activated upon detection of a significant frequency deviation, with the possibility to limit the support requested from other AC systems. It relies on an integral control enforcing the frequency droop characteristics (of classical speed governors), in addition to the voltage-droop control of VSCs. The controller is tuned to emulate the response of a power plant, while avoiding excessive transients in the HVDC system, and limiting the impact on the other AC systems.