Parametric Analysis and Optimization of a DC Current Flow Controller in Meshed MTDC Grids

A DC current flow controller (CFC) in a multi-terminal high-voltage direct current (HVDC) (MTDC) grid has the functionality of adjusting and optimizing the power flow on the DC lines. In this paper, the impact of DC CFC parameters on the system stability and dynamic performance is analyzed with three contributions: 1) a mathematical model and a small-signal model of the DC CFC in a meshed MTDC grid are derived; 2) considering the impact of controller parameters on gain margins, phase margins, and cut-off frequencies, the stability analysis is performed in the frequency domain and a parametric optimization scheme is proposed with the deployment of the control variate method and scanning method; 3) a method is proposed to determine the size range and the voltage reference of the common capacitance based on their influence on dynamic behaviors. Two DC CFC equipped multi-terminal meshed HVDC grids are established in PSCAD/EMTDC. The simulation results justify the effectiveness of the theoretical analysis. The proposed parametric selection scheme is demonstrated by dynamic responses shown in the comparative studies.