A Sequential AC/DC Power Flow Algorithm for Networks Containing Multi-terminal VSC HVDC Systems

In this paper, a sequential AC/DC power flow algorithm is proposed to solve networks containing Multi-terminal Voltage Source Converter High Voltage Direct Current (VSC MTDC) systems. In VSC HVDC technology, the converter losses add up to a significant fraction of the overall system losses. However, they are often neglected or not taken into account in a proper manner in VSC HVDC power flows. The algorithm put forward in this paper takes the converter losses into account using a generalized converter loss model. The converter steady state equations are derived in their most general format, with the AC network power injections as controlled quantities. It is shown that correctly defining the power setpoints with respect to the system bus instead of the converter bus, as is often done to simplify calculations, requires additional iterative calculations. The DC system modelling method proposed in this paper does not impose any restriction on the HVDC grid topology. A VSC MTDC power flow solver is incorporated into MATPOWER to show the validity of the proposed algorithm.