Boosting the efficiency of flexibility provision in modern TSO-DSO coordination mechanisms

Flexibility coordination between the transmission system operator (TSO) and the distribution system operator (DSO) involves the DSO solving an optimization program to trace the limits of its flexibility potential. The optimization objective also involves a penalty on deviation from an agreed active-power profile when the DSO is mapping the reactive power flexibility potential or minimizing flexibility cost. This paper proposes a number of improvements on the optimization problem carried out by the DSO in a multi-period setting. The paper presents a revised mathematical expression of flexibility, and the possibility to request particular flexibility patterns to emphasize flexibility provision for certain time periods. The proposed enhancements bring along a sizable increase in the flexibility potential, without impact on the computation time. The penalty scheme is also modified, and the existing mixed integer quadratic program formulation is replaced by a mixed integer linear program, thus, bringing forward a significant reduction in solution time. The proposed flexibility coordination formulation across 24 coupled periods is tested on the 34-bus distribution test system for five flexibility patterns. This paper is built upon previous work by the authors, which developed a sequential linear program algorithm, linearized the non-linear optimal power flow problem, and consequently, solved a stochastic multi-period optimal power flow problem.