Reducing HVDC Network Oscillations Considering Wind Intermittency Through Optimized Grid Expansion Decision

This paper considers the evolution of independent offshore HVDC links into a multi-terminal network. It proposes a control strategy to maximize the DC voltage stability under the worst-case perturbation scenario and considers the intermittent nature of the power injection from connected wind farms. A decentralized linear feedback controller achieving the minimization of the DC voltage oscillations, while ensuring control input constraints (i.e. reference currents) compliance, is proposed. The motivation of this framework is to include the DC voltage stability maximization under the worst-case perturbation as an additional decision criterion in a multi-objective optimization for HVDC network expansion decision. The other criteria can include for instance, length or cost of a line or the power losses along the line. To evaluate the applicability of the proposed method, placement of a new HVDC link between two independent VSC-based point-to-point HVDC grids located in the North Sea is assessed, using real wind data for a 4-terminal test grid.