  Multi-terminal high voltage direct current (MTHVDC) technology is a promising
technology for the offshore wind farm integration, which requires the new
control and operation scheme. Therefore, the optimal power flow problem for
this system is important to achieve the optimal economic operation. In this
paper, convex relaxation model based on semidefinite programming for the
MT-HVDC system considering DC/DC converters is proposed to solve the optimal
power flow problem. A hybrid AC and MT-HVDC system for offshore wind farm
integration is used for the test. The simulation results validate the
effectiveness of the proposed model and guarantee that the global optimum
solution is achieved.
