Universal branch model for the solution of optimal power flows in hybrid AC/DC grids

Abstract

This paper presents a universal model formulation for solving Optimal Power Flows for hybrid AC/DC grids. The prowess of the new formulation is that it (i) provides a direct link between AC and DC parts of the grid allowing for solving the entire network within a unified frame of reference (not sequentially) and (ii) can realistically model any element within the AC/DC power grid, ranging from conventional AC transmission lines to multiple types of AC/DC interface devices such as Voltage Source Converters (VSC) by introducing additional control variables. The model is formulated in such a way that it does not make a distinction, from a mathematical perspective, between AC and DC elements and the ensuing optimal power flow (OPF) problem can be solved via model-based optimization solvers as a mathematical programming problem. Simulations carried out using a variety of non-linear gradient-based solvers in AIMMS© on a small contrived and a large realistic test system (modified PEGASE) clearly show that the universal model is on par with existing methodologies for solving OPFs both in accuracy of the solution and computational efficiency. Meanwhile, simulations carried out on a series of AC and AC/DC test systems show that the model is scalable and stays computationally tractable for larger system sizes without sacrificing convergence time.