A Hybrid Transmission Grid Architecture Enabling Efficient Optimal Power Flow

Abstract

Abstract-The recent rise of electricity generation based on renewable energy sources increases the demand for transmission capacity. Capacity expansion via the upgrade of transmission line capacity, e.g., by conversion to a high-voltage direct current (HVDC) line, is an attractive option. In this paper, it is shown that if the upgrade to HVDC is applied systematically to selected transmission lines across the grid, a hybrid architecture is obtained that enables an efficient and globally optimal solution of the optimal power flow (OPF) problem. More precisely, for conventional meshed AC transmission grids the OPF problem is nonconvex and in general NP-hard, rendering it hard to solve. We prove that after the upgrade to the proposed hybrid architecture, the same mesh topology facilitates an exact convex relaxation of the OPF problem, enabling its globally optimal solution with efficient polynomial time algorithms. This OPF method is then employed in simulations, which demonstrate that the hybrid architecture can increase the effective transmission capacity and substantially reduce the generation costs, even compared to the AC grid with optimal transmission switching.Index Terms-Congestion management, convex relaxation, economic dispatch, HVDC transmission, optimal power flow, optimal transmission switching, power system design, power system management, semidefinite program, transmission capacity.

hynet: An Optimal Power Flow Framework for Hybrid AC/DC Power Systems

“…• System model for hybrid AC/DC power systems: By introducing a new network topology model as well as a set of definitions, we generalize the electrical model for AC grids in [34] and [35] to AC and DC subgrids and develop a unified AC/DC subgrid model. This is complemented by a new converter model that balances modeling depth and complexity to offer adequate accuracy based on a concise and flexible parameterization.…”

“…The set of natural numbers is denoted by N, the set of integers by Z, the set of real numbers by R, the set of nonnegative real numbers by R + , the set of positive real numbers by R ++ , the set of complex numbers by C, and the set of Hermitian matrices in C N ×N by S N . The imaginary unit [34] with an injection port (circles) and a branch port (triangles). (b) Model for branch k ∈ E [34], which connects the branch port of source busˆ (k) to the branch port of destination busˇ (k).…”

“…The imaginary unit [34] with an injection port (circles) and a branch port (triangles). (b) Model for branch k ∈ E [34], which connects the branch port of source busˆ (k) to the branch port of destination busˇ (k). (c) Model for converter l ∈ C, which connects the injection port of source busγ(l) to the injection port of destination busγ(l).…”

“…[28]- [33] and the references therein. However, besides the huge body of literature on convex relaxation for AC grids, only some works consider hybrid AC/DC grids with P2P- [34], [35] and MT-HVDC systems [19], [20], [36], [37].…”

Feature- and Structure-Preserving Network Reduction for Large-Scale Transmission Grids

“…The number of cycles is relevant in certain expansion strategies, e.g. the hybrid architecture[23],[25],[26].…”