DC voltage droop control design for multi-terminal HVDC systems considering AC and DC grid dynamics

This article is focused on the droop-based DC voltage control design for multi-terminal VSC-HVDC grid systems, considering the AC and the DC system dynamics. The droop control design relies on detailed linearized models of the complete multi-terminal grid, including the different system dynamics, such as the DC grid, the AC grid, the AC connection filters and the converter inner controllers. Based on the derived linear models, classical and modern control techniques are applied to design the different controllers, including a multi-variable frequency analysis to design the grid voltage droop control. In combination with the droop control, a DC oscillation damping scheme is proposed, in order to improve the system performance. The control design is validated through simulations of a three terminal system.