Power Flow Study of MT-HVDC Grid Compensated by Multiport Interline DC Power Flow Controller

Abstract

DC power flow controllers (DCPFCs) are emerging devices to control power flow in voltage source converter (VSC)-based multi-terminal HVDC (MT-HVDC) grids. In this paper, a novel Newton-Raphson (NR)-based DC power flow solver (DCPFS) is proposed to solve the DC power flow problem (DCPFP) by using a novel multiport interline DC power flow controller (MIDCPFC), where physical and control state variables of the whole system (MIDCPFC and MT-HVDC grid) are modified simultaneously to achieve predetermined control objectives. The static model (SM) and the power injection model (PIM) of the considered MIDCPFC have been derived and their equations are embedded within the proposed DCPFS. Since there are no fictitious buses in the proposed DCPFS, the original conductance matrix of the system and its symmetry are preserved, and only minor modifications are needed on the original system's Jacobin matrix. It is very straightforward to implement the proposed DCPFS as the voltage of intermediate capacitor of the MIDCPFC is treated as an independent variable, and thus, an external process to control its value is not needed. In this study, comprehensive models have been proposed to model losses of the MIDCPFC and VSCs for the first time; and the shunt conductance of HVDC lines have also been considered. Finally, a modified 15-bus MT-HVDC grid is proposed for verification purposes. The obtained results verify the accuracy and efficacy of the proposed concepts, models, and formulations of this study.