Multistage Robust Optimization for Time-Decoupled Power Flexibility Aggregation with Energy Storage

TL;DR

This paper introduces a multistage robust optimization model for power flexibility aggregation by DSOs, incorporating decision-dependent uncertainty and multiple solution methods, validated through case studies for practical effectiveness.

Contribution

It presents a novel multistage robust optimization framework for DSO power flexibility aggregation, capturing sequential decisions and accommodating non-ideal energy storage systems.

Findings

Rectangular method provides greater flexibility than existing approaches.

Proposed methods are effective and computationally efficient.

Case studies validate practical applicability of the models.

Abstract

To mitigate global climate change, distributed energy resources (DERs), such as distributed generators, flexible loads, and energy storage systems (ESSs), have witnessed rapid growth in power distribution systems. When properly managed, these DERs can provide significant flexibility to power systems, enhancing both reliability and economic efficiency. Due to their relatively small scale, DERs are typically managed by the distribution system operator (DSO), who interacts with the transmission system operator (TSO) on their behalf. Specifically, the DSO aggregates the power flexibility of the DERs under its control, representing it as a feasible variation range of aggregate active power at the substation level. This flexibility range is submitted to the TSO, who determines a setpoint within that range. The DSO then disaggregates the setpoint to dispatch DERs. This paper focuses on the DSO's power flexibility aggregation problem. First, we propose a novel multistage robust optimization model with decision-dependent uncertainty for power flexibility aggregation. Distinct from the traditional two-stage models, our multistage framework captures the sequential decision-making of the TSO and DSO and is more general (e.g., can accommodate non-ideal ESSs). Then, we develop multiple solution methods, including exact, inner, and outer approximation approaches under different assumptions, and compare their performance in terms of applicability, optimality, and computational efficiency. Furthermore, we design greedy algorithms for DSO's real-time disaggregation. We prove that the rectangular method yields greater total aggregate flexibility compared to the existing approach. Case studies demonstrate the effectiveness of the proposed aggregation and disaggregation methods, validating their practical applicability.