Optimal Power Flow in Multi-Terminal HVDC Systems

This paper presents an optimal power flow (OPF) analysis of a multi-terminal high-voltage direct current (HVDC) system. The objective of the OPF analysis in this paper is to minimize not only the losses in the lines and the converters but also the generation cost by using a multi-objective function, which makes the system economically efficient. The constraints of voltages, both of the DC and AC power flows, and the line flows are the parameters that affect the optimization process. The proposed methodology covers both the AC and DC sides of the grid in terms of the lines as well as the DC/DC and AC/DC converter losses. In order to achieve a global optimal solution of the OPF problem, semidefinite programming (SDP) is used. SDP has been tested on an 8-bus system with one DC/DC converter and five AC/DC converters. The result of the optimization process is obtained and a comparison is made between neglecting and including the losses of the AC/DC and DC/DC converters.