Quasi-AC Optimal Power Flow for VSC-MTDC Systems

The development of DC technology promotes the transformation of AC grid to AC/DC hybrid grid, this means that the existing optimal power flow(OPF) algorithm for only AC grid cannot meet the demand. A quasi-AC solution for OPF of voltage source converter based multi-terminal DC(VSC-MTDC) system is proposed. By analysing the principle of VSC, the equivalent model considering the loss of the converter station is established with AC power supply. Constraints are added to the DC grid to equivalent it to special AC grid. The energy coupling equation of the VSC is linearized to simplify the difficulty. Based on above, the power flow of VSC-MTDC system can be calculated as AC system. Since the OPF problem of AC system is non-convex, the OPF model is relaxed to a semi-definite programming model. The experimental result of the improved IEEE30-bus system shows that the proposed method can extend the OPF solution for traditional AC system to VSC-MTDC system and accurately reflect the internal loss of converter.