Ramping-aware Enhanced Flexibility Aggregation of Distributed Generation with Energy Storage in Power Distribution Networks

TL;DR

This work tackles the challenge of ramp-rate constraints in aggregating DER flexibility by formulating a ramping-aware envelope at the transmission–distribution boundary. It develops a baseline inner-box envelope using a linear program that jointly respects DER and distribution-network constraints, with provable disaggregation guarantees for any interior trajectory. To overcome conservativeness, the authors introduce a pre-ramping strategy that repositions operating points before each interval, expanding the envelope while preserving feasibility and disaggregation, and they validate the approach on the IEEE-33 bus system, including FRP-market economics and robustness to forecast errors. Results show notable improvements in deliverable flexibility (up to about 19% depending on conditions) and enhanced economics from reserve and FRP services, highlighting practical potential for TSO–DSO coordination.

Abstract

Power distribution networks are increasingly hosting controllable and flexible distributed energy resources (DERs) that, when aggregated, can provide ancillary support to transmission systems. However, existing aggregation schemes often ignore the ramping constraints of these DERs, which can render them impractical in real deployments. This work proposes a ramping-aware flexibility aggregation scheme, computed at the transmission-distribution boundary, that explicitly accounts for DER ramp limits and yields flexibility envelopes that are provably disaggregable. To further enhance the attainable flexibility region, we introduce a novel pre-ramping strategy, which proactively adjusts resource operating points to enlarge the aggregated flexibility envelope while preserving both network feasibility and disaggregation guarantees. The proposed method demonstrates a 5.2% to 19.2% improvement in flexibility relative to the baseline model, depending on system conditions. We validate the scheme on an IEEE-33 bus distribution system and provide formal proofs showing that both aggregation strategies are disaggregable for all feasible trajectories within the aggregate flexibility envelope.

Figures (4)

• Figure 1: Comparison of upward flexibility with and without pre-ramping. As shown, the upward flexibility increases from $p_g + R^{\uparrow} + p_e$ to $p_g + R^{\uparrow} + p_e + p^{\mathrm{pre}}$, where $p^{\mathrm{pre}}$ captures the additional ramp-up capability provided by pre-ramping.
• Figure 2: Comparison of disaggregation feasibility for various GCP flexibility envelope models. Positive values represent power export from the distribution system to the upstream grid. (a) envelope neglecting ramp-rate constraints where red trajectories indicate infeasible disaggregation, (b) the baseline model considering ramping limits, and (c) the proposed enhanced model with pre-ramping decisions.
• Figure 3: Aggregate power trajectories at the GCP in Case II. The black line denotes the base (reference) dispatch.
• Figure 4: Generator output trajectories in Case II corresponding to the aggregate trajectories at the GCP. The black line denotes the base (reference) dispatch.