Enhanced multi-terminal HVDC grid management for reliable AC network integration

This paper presents a secondary control for MTDC systems to update the DC voltage and converter power references of the VSC stations operating under droop control, in order to eliminate the large power deviation from their desired reference power. The rated values of the VSC station used as reference does not take into account the power losses in the converter, DC line and the voltage drops in the DC transmission lines. This creates a constant difference between rated DC voltage reference and actual DC voltage value of the VSC station. This difference is multiplied by the droop gain of the VSC station, hence causing power deviations in the MTDC grid system. In this paper a secondary control is implemented for a four-terminal HVDC system modelled in EMTDC/PSCAD, to demonstrate the reduction in power deviation by the proposed secondary control.