A General Unified AC/DC Power Flow Algorithm With MTDC

The aim of this paper is to derive a general AC/DC power flow model with Voltage Source Converter Multi-Terminal High-Voltage Direct Current Systems (VSC MTDCs). The equations of AC, DC grids, and VSCs are formulated in augmented rectangular coordinates. The proposed model is composed of two nodal equations and two power constraints for each AC bus, as well as one nodal equation and one power constraint for each DC bus. In this model, the VSC equations are included in the AC and DC grid model—its power balance equation and one of the control equations are regarded as the power constraints of the AC bus connected to it, whereas the other control equation is regarded as the power constraint of the DC bus connected to it. Therefore, the number of equations of the proposed model is determined only by that of AC and DC buses, and the model is systematically well organized; the variety of VSC control strategies and AC/DC linking configurations does not influence the overall structure. The proposed approach enables to solve the load flow of the most general AC/MTDC, consisting of multiple AC and DC grids connected by VSCs, and is suitable for control strategies including the droop control and any new ones in the future. The model also leads to higher computational efficiency. By demonstrations on AC/DC power systems with several VSCs, this method is proved to be effective, flexible, and efficient.