Evaluation of DC voltage control strategies for multi-terminal HVDC grids comprising island systems with high RES penetration

The main objective of this paper is to evaluate alternative DC power flow control strategies applied to Multi-Terminal HVDC (MTDC) grids comprising island systems with high Renewable Energy Source (RES) penetration. A statistical assessment is first performed by calculating the expected steady-state DC voltage and power flow variations of the MTDC grid, induced by stochastic variations of the imported or exported power of each island system. The control strategies applied to the onshore converter controllers comprise predefined voltage - power regulation characteristics, which do not rely on communication infrastructure, such as droop control, voltage margin control, as well as droop control with dead-band. Further, a dynamic model is introduced for the MTDC grid in order to investigate its dynamic behaviour in outage conditions, i.e. following the sudden loss of an onshore converter. For this purpose, suitable control schemes are proposed for the island converters, capable of handling the power imbalance of the MTDC grid.