Virtual inertia control and voltage support in MMC-based DC systems

Flexible DC transmission technology is developing rapidly, which is a better way to integrate distributed energy and long-distance power transmission. However the double loop control mode or vector control scheme provides almost no inertia to the AC system that decreases the stability of the grid during faults or other disturbances. In order to provide an improved control scheme, the key is to change the voltage source converter from taking the conventional control strategy to a frequency sensitive way. In this paper, the comparison between traditional synchronous machine and the present voltage source converter is presented. The role of MMC during transient period including virtual inertia control principle is discussed. The factors that may affects the deviation of frequency are explored. Finally, the performance of these strategies are evaluated for transients based on a MMC-HVDC system by PSCAD/EMTDC.