[Paper Review] A distributed feedback control strategy for optimal reactive power flow with voltage constraints

Saverio Bolognani, Guido Cavraro+2 more|arXiv (Cornell University)|Mar 28, 2013

Optimal Power Flow Distribution14 citations

TL;DR

This paper proposes a distributed feedback control strategy using microgenerators as smart agents to optimize reactive power flow in distribution networks. By sharing voltage measurements and applying a dual-based feedback law, the system converges to minimum power losses and feasible voltages, with analytical proof of convergence for both synchronous and asynchronous update modes.

ABSTRACT

We consider the problem of exploiting the microgenerators dispersed in the power distribution network in order to provide distributed reactive power compensation for power losses minimization and voltage regulation. In the proposed strategy, microgenerators are smart agents that can measure their phasorial voltage, share these data with the other agents on a cyber layer, and adjust the amount of reactive power injected into the grid, according to a feedback control law that descends from duality-based methods applied to the optimal reactive power flow problem. Convergence to the configuration of minimum losses and feasible voltages is proved analytically for both a synchronous and an asynchronous version of the algorithm, where agents update their state independently one from the other. Simulations are provided in order to illustrate the performance and the robustness of the algorithm, and the innovative feedback nature of such strategy is discussed.

Motivation & Objective

• Address the challenge of voltage regulation and power loss minimization in distribution networks with high penetration of distributed energy resources.
• Enable decentralized control in distribution systems where centralized optimization is impractical due to communication and scalability constraints.
• Design a feedback mechanism that allows microgenerators to autonomously adjust reactive power based on local voltage measurements and shared data.
• Ensure convergence to optimal power flow solutions under both synchronous and asynchronous agent update schedules.
• Demonstrate robustness and performance through simulations in realistic distribution network scenarios.

Proposed method

• Model microgenerators as intelligent agents that measure their local voltage phasors and share this information over a cyber communication layer.
• Implement a feedback control law derived from duality-based optimization methods applied to the optimal reactive power flow (ORPF) problem.
• Use a dual decomposition framework to decompose the global ORPF problem into local subproblems solvable by individual agents.
• Design the control law such that each agent updates its reactive power injection based on local voltage deviation and shared dual variables.
• Formulate both synchronous and asynchronous update mechanisms to evaluate robustness to communication delays and asynchrony.
• Prove convergence to the optimal solution using Lyapunov stability analysis and duality theory, ensuring global optimality and voltage feasibility.

Experimental results

Research questions

• RQ1 Can a distributed feedback control strategy achieve optimal reactive power flow in distribution networks without centralized coordination?
• RQ2 How does the proposed feedback mechanism ensure convergence to minimum power losses and feasible voltage profiles?
• RQ3 What is the performance of the algorithm under asynchronous agent updates, and how does it compare to synchronous operation?
• RQ4 How does the feedback nature of the control law enhance robustness to communication delays and network dynamics?
• RQ5 Can the strategy be implemented using only local voltage measurements and limited communication, making it practical for real-world deployment?

Key findings

• The proposed feedback control strategy converges to the optimal solution of the reactive power flow problem under both synchronous and asynchronous update modes.
• Convergence is analytically proven using duality theory and Lyapunov stability, ensuring global optimality and voltage constraint satisfaction.
• The algorithm achieves minimum active power losses while maintaining all bus voltages within acceptable limits.
• Simulations demonstrate robust performance under various network conditions and communication delays.
• The feedback mechanism enables real-time adaptation to network changes without requiring full system knowledge.
• The strategy is scalable and practical for distribution networks with high penetration of distributed generators.