A Primal-Dual Interior-Point algorithm for nonlinear ACOPF with adaptively reformulated Volt-Var constraints

• We develop a nonlinear optimization tool for distribution network management. • We integrate volt-var constraints into a nonlinear AC optimal power flow. • We develop an algorithm that adaptively reformulates the volt-var constraints. • We validate our approach on the IEEE 33-bus network. • We assess scalability and convergence on a large set of distribution networks. The increasing penetration of generation from renewable energy sources in distribution networks poses significant challenges for voltage regulation and network operation. Automatic volt-var control is widely adopted to address voltage issues; however, its integration into optimization-based distribution network management frameworks is often addressed through simplified approximations or multi-stage coordination schemes, which may compromise physical accuracy or computational efficiency. We develop an Interior-Point-based solution approach that embeds volt-var curves directly within a nonlinear AC optimal power flow (ACOPF) formulation, enabling coordinated centralized and local control in power distribution networks. The resulting formulation allows solving the problem without the use of linearizations, convex relaxations, or mixed-integer representations. An extensive computational study covering a large set of distribution network instances demonstrates the scalability, robustness, and practical applicability of the proposed approach.