Providing Curative Distribution Grid Flexibility Using Online Feedback Optimization

Distribution grid flexibility is regarded as a possible measure in curative system operation, yielding a need for an efficient and robust coordination mechanism for the joint flexibility provision by individual units to the transmission grid. This paper introduces a method to coordinate distribution grid level flexibility as a fast-responding curative measure based on Online Feedback optimization. We utilize an optimization algorithm in a closed loop with the distribution grid to dispatch set points for active and reactive power to flexibility providing units. The approach is evaluated in an experimental setup, utilizing assets connected to an exemplary low voltage grid. Online Feedback optimization is found to be both a viable as well as a highly effective approach to coordinate distributed energy resources in real-time curative system operation.

I. Introduction

Curative operation of energy transmission systems is a promising approach to allow for more efficient utilization of existing operating resources, therefore reducing the need for expensive preventive re-dispatch, while maintaining a high level of security in online system operation [1]. Such curative operation becomes possible through fast-responding measures, that are able to reduce line loading below the permanently admissible limits (PATL) in case of an overload within a short interval of time, ranging from several seconds to several minutes. One curative measure under discussion is a provision of flexibility by distribution grids at the point of common coupling (PCC) between transmission system operator (TSO) and distribution system operator (DSO) as shown in Fig. 1. In case of an overloaded transmission line, the requested flexibility has to be coordinated by the DSO to a possibly high number of flexibility providing units (FPU), which leads to a need for efficient and reliable coordination mechanisms.