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Subtransmission Grid Control via Online Feedback Optimization

Lukas Ortmann, Jean Maeght, Patrick Panciatici, Florian Dörfler, Saverio Bolognani

TL;DR

The paper tackles real-time congestion management and voltage control in subtransmission grids with high renewable penetration by extending Online Feedback Optimization (OFO) to handle discrete actuators like on-load tap changers. It introduces the Unicorn 7019 Blocaux benchmark to evaluate OFO in a realistic setting, formulates a MIQP-based projection step, and demonstrates robust constraint satisfaction and high wind-injection performance under model mismatch. Key contributions include a practical tuning framework (via the G matrix), integration of active/reactive power injections with tap changes, and two tasks validating optimal curtailment and voltage support. Results show OFO can operate the real grid safely at or near the time-varying optimum, with significant improvements over fixed-curtailment practices and the ability to include ancillary services in the control objective."

Abstract

The increasing electric power consumption and the shift towards renewable energy resources demand for new ways to operate transmission and subtransmission grids. Online Feedback Optimization (OFO) is a feedback real-time control method that can be employed to enable optimal operation of these grids. Such controllers can maximize grid efficiency (e.g., minimizing curtailment) while satisfying grid constraints like voltage and current limits. The OFO control method is tailored and extended to handle discrete inputs and it is explained how to design an OFO controller for the subtransmission grid. A novel benchmark is presented and published that corresponds to the real French subtransmission grid on which the proposed controller is analyzed in terms of robustness against model mismatch, constraint satisfaction, and tracking performance. It is shown that OFO controllers can help utilize the grid to its full extent, virtually reinforce it, and operate it optimally and in real-time by using the flexibility offered by renewable generators connected to distribution grids.

Subtransmission Grid Control via Online Feedback Optimization

TL;DR

The paper tackles real-time congestion management and voltage control in subtransmission grids with high renewable penetration by extending Online Feedback Optimization (OFO) to handle discrete actuators like on-load tap changers. It introduces the Unicorn 7019 Blocaux benchmark to evaluate OFO in a realistic setting, formulates a MIQP-based projection step, and demonstrates robust constraint satisfaction and high wind-injection performance under model mismatch. Key contributions include a practical tuning framework (via the G matrix), integration of active/reactive power injections with tap changes, and two tasks validating optimal curtailment and voltage support. Results show OFO can operate the real grid safely at or near the time-varying optimum, with significant improvements over fixed-curtailment practices and the ability to include ancillary services in the control objective."

Abstract

The increasing electric power consumption and the shift towards renewable energy resources demand for new ways to operate transmission and subtransmission grids. Online Feedback Optimization (OFO) is a feedback real-time control method that can be employed to enable optimal operation of these grids. Such controllers can maximize grid efficiency (e.g., minimizing curtailment) while satisfying grid constraints like voltage and current limits. The OFO control method is tailored and extended to handle discrete inputs and it is explained how to design an OFO controller for the subtransmission grid. A novel benchmark is presented and published that corresponds to the real French subtransmission grid on which the proposed controller is analyzed in terms of robustness against model mismatch, constraint satisfaction, and tracking performance. It is shown that OFO controllers can help utilize the grid to its full extent, virtually reinforce it, and operate it optimally and in real-time by using the flexibility offered by renewable generators connected to distribution grids.
Paper Structure (22 sections, 7 equations, 9 figures, 1 table)

This paper contains 22 sections, 7 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. The Unicorn 7019 Benchmark
  3. Online Feedback Optimization with Integer Constraints
  4. Input, Output, and Optimization Problem
  5. OFO Controller
  6. Controller Tuning
  7. Rate of change of different inputs
  8. Tap changer usage
  9. Necessary Model Information
  10. Comparison between Offline Optimization and OFO
  11. Controller Design for the Blocaux Area
  12. Constraint Sets and Integer Constraints
  13. Sensitivities
  14. Cost Function
  15. Tuning Parameters and Sampling Time
  16. ...and 7 more sections

Figures (9)

  • Figure 1: The Blocaux area with 31 buses, 58 branches, and 42 wind farms with a total power of 1274 MW. Connections to the rest of France are indicated with dashed lines. The tap changers are on the transformers connecting the different voltage levels.
  • Figure 2: Block diagram of the control setup with the controller in blue and the grid in gray.
  • Figure 3: Offline vs. Online Feedback Optimization.
  • Figure 4: Simulation of the Unicorn benchmark under time-varying wind power (blue line in top right plot). The lower three plots show the control inputs and the upper plots show the resulting voltages, line usage, and used wind power. The voltage constraints that the controller has to enforce are the real French grid limits.
  • Figure 5: Closeup of the tap changer behavior between minutes 14 and 18.
  • ...and 4 more figures