A Variable Droop Coefficient Control of Soft Open Point Based on Adaptive Virtual Inertia

Soft open point (SOP) is a new type of power electronic devices that may replace traditional tie switches in some key nodes of distribution networks (DNs). In this paper, considering the lack of inertia of the power system, the system stability problem and power quality problems of DN s are more serious than ever before, a variable droop coefficient control based on multi-terminal SOP is proposed to enhance robust performance and stability of DNs. Because of the similarity between the rotor equation of synchronous motor and the dynamic equation of DC capacitance of SOP, the frequency of AC system is coupled with the DC voltage of SOP via a variable droop coefficient. The key to adjust the droop coefficient is to adjust the virtual inertia according to the AC system frequency deviation. Thus the variable droop coefficient control of SOP realizes adaptive virtual inertia, allowing the SOP provide optimal inertia support to DNs. Then a four-terminal SOP system model is built based on PSCAD/EMTDC, and the simulation results prove the validity and correctness of the control strategy.