hynet: An Optimal Power Flow Framework for Hybrid AC/DC Power Systems
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High-voltage direct current (HVDC) systems are increasingly incorporated into today's AC power grids, necessitating optimal power flow (OPF) tools for the analysis, planning, and operation of such hybrid systems. To this end, we introduce hynet, a Python-based open-source OPF framework for hybrid AC/DC grids with point-to-point and radial multi-terminal HVDC systems. hynet's software design promotes ease of use, extensibility, and a manifold of solving options, which range from interior-point methods to relaxation-based solution techniques. This paper introduces the underlying mathematical framework, including the system model and OPF formulation. To support large-scale hybrid grids, the presented model balances modeling depth and complexity to offer both adequate accuracy and computational tractability. Additionally, the OPF formulation is simplified by a proposed state space relaxation that unifies the representation of AC and DC subgrids. Furthermore, two supported convex relaxations of the OPF problem and some related results are discussed and generalized. Finally, hynet's software design is illustrated and related to the presented mathematical framework, while highlighting its amenability to extensions.
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