Providing Curative Distribution Grid Flexibility Using Online Feedback Optimization

TL;DR

The paper addresses curative grid operation by coordinating distribution-grid flexibility at the PCC using Online Feedback Optimization (OFO) in a closed-loop controller. The approach formulates a convex-like objective, $\Phi = \sum_{i\in F}(P_i^2+Q_i^2)$, with voltage and device constraints, and solves it in real time by projecting gradients onto feasible setpoints via an internal QP, while leveraging online measurements to compensate for model mismatch. The experimental LV-grid validation demonstrates that OFO can disaggregate a PCC flexibility request to distributed FPUs, achieving rapid response (e.g., $\Delta t$ on the order of seconds) and robustness against disturbances such as EV charging and fluctuating PCC voltages, with minimal reliance on detailed grid models. The findings indicate that OFO is a viable, efficient alternative to OPF-based coordination for curative distribution-grid flexibility, enabling fast relief of overloads with improved reliability, and motivating exploration of multi-controller cascades across grid layers.

Abstract

Distribution grid flexibility is discussed 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.

Figures (8)

• Figure 1: Provision of flexibility by distribution grids after an overload on a superimposed transmission line.
• Figure 2: Interface between OFO-based operational control unit and physical distribution grid with FPU in laboratory setup.
• Figure 3: Control loop: OFO controller in a closed loop with distribution grid.
• Figure 4: Full laboratory setup used for experimental validation.
• Figure 5: Coordination of $14.5 \text{kW}$ flexible active power by OFO algorithm.