Droop Control Optimization for Multi-Terminal HVDC Transmission System

This paper proposes a method to determine optimal voltage droop control values for converters in a VSC-based multi terminal HVDC system (MTDC). The modelled MTDC system is obtained by connecting a wind-farm to an existing point-to-point (PtP) cable connection between two onshore converter stations. The challenge with such arrangement is to control the share of power between the two onshore converters. In order to overcome this problem, the DC voltage droop control will be implemented. In the end of the paper, a guideline will be presented to dictate how the power is shared between two converters in a 3-terminal MTDC system. The guideline explain how to determine the optimal droop constants k(v), which is influenced by transmission losses, cable length between stations, converter limits (active power- and voltage limits) and their sensitivity regarding droop values. The results shows that different factors affect the choice of the droop constant.