A Linearized AC-OPF Framework for Re-dispatch Optimization

The generation shift towards renewable energy sources (RES) along with challenging grid expansion measures lead to a higher utilization of transmission systems. As a result, congestion management measures have been becoming more important for secure grid operation. The choice of these measures is highly complex due to economic and technical interdependencies. Here, the formulation as an optimal power flow (OPF) problem can support the decision-making. While AC-OPF problems contain nonlinear, nonconvex formulations which makes them computational challenging, DC-OPF only considers active power flows which, for some applications, is not sufficient. This paper presents a new approach to avoid this major drawback: a linearized AC-OPF for re-dispatch optimization. Both active and reactive power flows are formulated as linear network constraints by using linearization and relaxation of the trigonometric functions. The feed-in priority of RES as well as the (n-1) security are taken into account. The application of the developed methodology to a benchmark grid model shows that the optimization results in a good approximation of the actual power flows. This enables the determination of cost-optimal measures that effectively remedy the grid congestion. As potential application of the developed optimization, a case study on the curtailment of RES is carried out. The analysis shows that excluding RES from the congestion management results in up to three times higher costs in particular snapshots of the respective benchmark.