Optimal dc reference voltage in HVDC grids

In a HVDC grid, power energy equilibrium must be guaranteed at every moment to prevent DC voltage to increase or decrease to unacceptable values. Contrary to the frequency in an AC power system, the DC voltage cannot be assumed to be the same throughout the system, since a DC voltage difference is necessary to have a current flow. To operate HVDC grids as far as possible from DC voltage stability limits, the selection of the DC reference voltage and DC reference node are crucial factors. This paper introduces a method to find the optimal DC voltage in a HVDC grid based on power flow and line resistances. The method is implemented in the open-source software MatACDC and the results are verified by dynamic simulations in DIgSILENT, using a one area DC voltage restoration controller.