Optimal Frequency Support from Virtual Power Plants: Minimal Reserve and Allocation

TL;DR

The paper tackles the challenge of providing fast frequency support in low-inertia power systems by forming a Virtual Power Plant (VPP) that aggregates inverter-based resources (IBRs) for dynamic frequency regulation. It introduces a reserve-minimizing framework that (i) models the VPP–grid interaction with an eighth-order state-space model and a reduced-order frequency response, (ii) enforces a decay-rate constraint and safety bounds to define a feasible region for VPP reserves, and (iii) allocates reserves across IBRs via an energy-based convex optimization. The two-stage ResMin algorithm yields minimal VPP reserves and improved economic outcomes, demonstrated on a modified IEEE-39 bus with eight IBRs, including robust allocations under renewable-uncertainty scenarios. The results show substantial reductions in idle reserves and enhanced market profitability, particularly as system inertia declines, while maintaining frequency safety. The work offers a practical path for VPPs to participate more effectively in real-time markets and provides a foundation for robust, uncertainty-aware reserve scheduling.

Abstract

This paper proposes a novel reserve-minimizing and allocation strategy for virtual power plants (VPPs) to deliver optimal frequency support. The proposed strategy enables VPPs, acting as aggregators for inverter-based resources (IBRs), to provide optimal frequency support economically. The proposed strategy captures time-varying active power injections, reducing the unnecessary redundancy compared to traditional fixed reserve schemes. Reserve requirements for the VPPs are determined based on system frequency response and safety constraints, ensuring efficient grid support. Furthermore, an energy-based allocation model decomposes power injections for each IBR, accounting for their specific limitations. Numerical experiments validate the feasibility of the proposed approach, highlighting significant financial gains for VPPs, especially as system inertia decreases due to higher renewable energy integration.

Figures (18)

• Figure 1: Fixed frequency regulation reserve ignores the dynamics on the timescale of seconds of VPP-level active power injections. The fixed reserve is determined by the peak value of active power injections, which contains the actual reserve and the idle one.
• Figure 2: A typical VPP system hosts a group of IBRs, including electrical vehicles, the wind farm and solar panels with battery storage systems. The energy managed by VPP is used for trade (financial gains) or reserve (frequency support).
• Figure 3: Overview of the proposed method to derive and allocate the regulation requirements.
• Figure 4: The current inner loop control diagram.
• Figure 5: The block diagram illustrates the system frequency response. The forward path represents the relationship between power disturbance and frequency deviation of the grid. While the green part and blue part describe the frequency responses of SGs and VPP, respectively.