Master's thesis and Internship : Strategies to Mitigate Market Re-Optimisation in Remedial Action Optimisation for Congestion Management in Transmission System Operators

Abstract

The increasing complexity of electrical transmission systems, driven by renewable energy integration, market liberalisation, and the growing number of controllable assets, increases the challenges of congestion management for transmission system operators (TSOs). To support operational decision-making, remedial action optimiser (RAO) is used to identify cost-efficient combinations of remedial actions that ensure system security while limiting market interventions.

However, cost-based optimisation may trigger market re-optimisation. In some situations, negative redispatch costs make additional market redispatch economically attractive, even beyond what is required to relieve congestion. Consequently, the optimiser may favour excessive redispatch and neglect TSO-controlled remedial actions, leading to market adjustments that reduce costs without improving system security.

This thesis investigates this issue through both theoretical analyses and numerical simulations. Several mitigation strategies are proposed: arbitrary modifications of redispatch cost structures, prohibition of negative costs and adding operational constraints. These approaches are first analysed on simplified test cases to understand their behaviour and limitations, and then the promising methods, the ones inducing arbitrary modifications in the redispatch costs, are evaluated on large-scale simulations of the Belgian transmission grid using the existing PowSyBl OpenRAO tool.

The results show that these methods effectively prevent market re-optimisation. However, by modifying redispatch costs, they introduce a systematic bias in the optimisation process. Even when redispatch combinations resulting in low real operational costs exist, the optimiser may favour more costly alternative redispatch actions that provide more effective congestion relief under the modified cost formulation. Consequently, the selected solutions generally involve lower redispatch volumes but can become more expensive when evaluated using the original cost structure. No single method fully resolves the market re-optimisation issue while avoiding this trade-off in all configurations.

These findings highlight the challenges of achieving a perfect solution within RAO frameworks and underline the unavoidable trade-off between economic efficiency and robustness in effective congestion management.