Coupling between the frequency droop and the voltage droop of an AC/DC converter in an MTDC system

MTDC systems are required to be reliable, and in certain cases, should participate in the AC grids frequency regulation. This can be achieved by providing AC/DC converters with a dual controller combining both the voltage-droop and the frequency-droop control techniques. In this paper, the coupling between the two droops is theoretically investigated and quantified for both a DC side fault and an AC side fault. A 5-terminal HVDC grid is simulated to validate the theoretical results.