Optimal Power Flow for Hybrid AC/MTDC Systems

With the recent advancements in the power electronics industry, high implementation of distributed energy resources and an increased number of sensitive AC and DC loads have led to unconventional hybrid AC/MTDC systems. This paper proposes an optimal power flow (OPF) for hybrid AC/MTDC (multi-terminal DC) systems while considering the losses of lines and converters. The impact of both is studied across the system to achieve an optimal solution using a semidefinite programming (SDP) algorithm. In addition, a multi-objective function is implemented to minimize the losses of lines and converters under a certain set of constraints covering both sides of the grid. The rationale of this paper is that the number of voltage source converters (VSCs) in distribution systems has boosted in recent years, which may result in considerable losses; therefore, an OPF-based SDP model is presented to obtain a global optimal result. The systems under test are a modified CIGRE B4 DC test system as well as an IEEE 33-bus hybrid AC/DC distribution system, both of which have been adapted to serve the purpose of this paper. The simulation results are conducted in a MATLAB environment to verify the effectiveness of the proposed technique.