多特蒙德工业大学

Several sources of flexibility in transmission and, especially, distribution networks are being unlocked by advances in information and communication technologies, aggregators, and new flexibility markets. However, maximizing benefits for both transmission and distribution system operators in a coordinated way requires new algorithms, modeling tools, and modernization of regulatory frameworks. Such approaches must account for uncertainties, the physical and operational constraints of flexibility providers and the grid itself, constraints on information exchange, and scalability, including computational requirements and time constraints. Given the diverse contexts and jurisdictions around the world, there is no single recipe for achieving coordination, but important trends and shared challenges are emerging. This paper surveys the complexities of coordination from technical, market, and technological perspectives, and outlines current practices, proposed approaches, and future research directions to effectively manage, coordinate, model, and leverage flexibility across voltage levels.

As converter-based generation becomes increasingly dominant, Grid-Forming (GFM) control plays a key role in regulating voltage and frequency. While various strategies have been proposed to improve GFM performance under large disturbances, most of them focus on balanced conditions. This work presents a direct Voltage Control GFM (VCGFM) that enhances the large disturbance stability under unbalanced scenarios. Building on a virtual power-based method previously validated in balanced cases, the VCGFM is extended to integrate a negative sequence control. A current limitation scheme is introduced to limit both positive and negative sequence currents. The proposed control is validated through numerical simulations and experimental tests under diverse balanced and unbalanced grid disturbances. The method aims to preserve the voltage-source behavior of the VCGFM while maintaining synchronization and limiting currents during severe asymmetrical faults.

Given a budget and an undirected graph with a cost and a profit function on the edges, the Edge Orienteering Problem asks for a closed walk in the graph that collects the most profit while the sum of costs does not exceed the budget. While the profit is collected only once per edge, the cost is incurred each time the edge is traversed by the walk. In this paper, we present a (4+ε)-approximation algorithm for the Edge Orienteering Problem.

To model mechanically driven phase transformations using the phase-field theory, suitable models are needed to describe the mechanical fields associated with the individual phase-fields in the interfacial regions. They play a crucial role in obtaining the mechanical driving forces of phase-field evolution. Quantitative modeling requires satisfying both the interfacial static equilibrium and kinematic compatibility conditions. To the best of our knowledge, no existing multi-phase-field elasticity model has been able to satisfy all the jump conditions between all the locally active phase-fields along the associated pairwise normals, except in the dual-phase-field regions. In this work, we introduce a novel multi-phase-field elasticity model based on the partial rank-one relaxation of the elastic energy density defined on the pairwise interfaces as a function of pairwise strains. These ad hoc pairwise definitions enable us to satisfy the static equilibrium and kinematic compatibility conditions between all the locally active phase-fields. Different numerical examples are presented that compare the developed model against the equal-strain and equal-stress limiting cases.