Optimal Transmission Switching and Busbar Splitting in Hybrid AC/DC Grids

TL;DR

This work introduces a full non-convex MINLP framework for joint Optimal Transmission Switching and Busbar Splitting in hybrid AC/DC grids, enabling switching actions across AC, DC, and converters. It implements multiple reformulations (SOC, QC, LPAC, and Big-M) to assess feasibility, optimality, and tractability across networks of increasing size. Across five test cases, topology actions reduce generation costs relative to AC-OPF, with LPAC-BS offering a favorable speed-accuracy trade-off for AC-feasible solutions in larger systems. The study highlights the practical potential of remedial topology optimization for future offshore HVDC-integrated grids while acknowledging scalability and data challenges for very large, realistic networks.

Abstract

Driven by global climate goals, an increasing amount of Renewable Energy Sources (RES) is currently being installed worldwide. Especially in the context of offshore wind integration, hybrid AC/DC grids are considered to be the most effective technology to transmit this RES power over long distances. As hybrid AC/DC systems develop, they are expected to become increasingly complex and meshed as the current AC system. Nevertheless, there is still limited literature on how to optimize hybrid AC/DC topologies while minimizing the total power generation cost. For this reason, this paper proposes a methodology to optimize the steady-state switching states of transmission lines and busbar configurations in hybrid AC/DC grids. The proposed optimization model includes optimal transmission switching (OTS) and busbar splitting (BS), which can be applied to both AC and DC parts of hybrid AC/DC grids. To solve the problem, a scalable and exact nonlinear, non-convex model using a big M approach is formulated. In addition, convex relaxations and linear approximations of the model are tested, and their accuracy, feasibility, and optimality are analyzed. The numerical experiments show that a solution to the combined OTS/BS problem can be found in acceptable computation time and that the investigated relaxations and linearisations provide AC feasible results.

Figures (7)

• Figure 1: Converter station model, figure from ergun_optimal_2019.
• Figure 2: DC (left) and AC (right) branch model.
• Figure 3: AC and DC switch models for busbar splitting.
• Figure 4: Busbar splitting representation with AC and DC switches for AC and DC busbars. Each grid element originally connected to the split busbars is attached to an auxiliary bus and linked to each part of the split busbar through a switch.
• Figure 5: Possible configurations of the exclusivity constraint for each network element connected to a busbar being split.