Distributed Online Feedback Optimization for Stable Voltage Regulation in Distribution Systems

Core Concepts

A nested feedback optimization approach is proposed to achieve stable and efficient distributed voltage regulation in distribution systems, outperforming both centralized and previous distributed methods.

Abstract

The content discusses the problem of voltage regulation in distribution systems with high penetration of distributed energy resources (DERs). It presents an online feedback optimization (OFO) approach to address this challenge in a distributed manner, without requiring a centralized communication architecture.
The key points are:

Centralized OFO approaches rely on a gather-and-broadcast communication model, which lacks robustness to single-point failures.

Previous distributed OFO approaches, such as the two-metric approach, may lead to algorithm instability and divergence.

To address this, the paper proposes a nested feedback optimization approach, where the outer loop performs the OFO iterations to obtain tentative reactive power setpoints, and the inner loop solves a non-Euclidean projection problem to map the tentative setpoints to actual feasible setpoints.

The proposed approach only requires short-range communication between physical neighbors, and simulation results show that it achieves even better voltage regulation performance than the centralized approach, while being more robust to system uncertainties and disturbances.

The nested approach does not extend to joint active and reactive power control, but the authors suggest deploying separate active and reactive power feedback controllers at different sampling times as a potential solution.

Stats

The average voltage violation (AVV) values are:
1.9 × 10^-4 pu for the centralized approach
1.3 × 10^-4 pu for the proposed approach
4.6 × 10^-3 pu for the two-metric approach

Quotes

"While the two-metric approach does not converge and fails to regulate voltages, our proposed approach converges quickly after approximately 154 iterations, which correspond to around 22 outer and 132 inner iterations."
"Our simulation results showed that the approach achieved even better voltage regulation than a centralized approach while only requiring short-range communication between physical neighbours."

Key Insights Distilled From

Stable Distributed Online Feedback Optimization for Distribution System Voltage Regulation

by Sen Zhan,Nik... at arxiv.org 05-07-2024

https://arxiv.org/pdf/2405.02487.pdf

Deeper Inquiries

How can the proposed nested feedback optimization approach be extended to handle joint active and reactive power control, while maintaining the distributed communication architecture and stability guarantees

To extend the proposed nested feedback optimization approach to handle joint active and reactive power control while maintaining the distributed communication architecture and stability guarantees, a few modifications can be implemented. Firstly, the algorithm can be adapted to consider the joint impact of active and reactive power injections on the voltage profile. This would involve updating the objective function to include both active and reactive power costs and constraints. The inner loop of the nested optimization can then be designed to optimize both active and reactive power setpoints simultaneously, ensuring that the voltage regulation objectives are met while considering the interdependence of active and reactive power.
Additionally, the communication strategy between physical neighbors can be enhanced to exchange information related to both active and reactive power requirements. By sharing local information on active and reactive power injections and voltage measurements, neighboring nodes can collaboratively optimize their power setpoints to achieve the desired voltage regulation targets. This distributed approach ensures that each node only requires local information for decision-making, maintaining the decentralized nature of the optimization process.
Furthermore, stability guarantees can be maintained by incorporating appropriate constraints and regularization terms in the optimization algorithm to prevent divergence or oscillations in the control actions. By carefully designing the feedback loops and projection steps to account for the joint control of active and reactive power, the proposed nested feedback optimization approach can effectively handle the complexities of managing both power components in distribution systems.

What are the potential trade-offs between the computational complexity and the performance of the nested feedback optimization approach compared to the centralized and previous distributed methods

The potential trade-offs between the computational complexity and the performance of the nested feedback optimization approach compared to centralized and previous distributed methods lie in the balance between optimization accuracy and real-time implementation feasibility. The nested feedback optimization approach introduces an additional layer of iterative optimization, which may increase computational complexity compared to simpler centralized or distributed methods. However, this increased complexity enables the approach to achieve better performance in terms of voltage regulation and constraint satisfaction.
The performance benefits of the nested feedback optimization approach include improved convergence speed, enhanced voltage regulation, and robustness to system uncertainties and disturbances. By iteratively refining the reactive power setpoints through the nested optimization process, the approach can adapt to changing system conditions and optimize power injections more effectively than traditional methods.
On the other hand, the increased computational complexity of the nested feedback optimization approach may pose challenges in real-time implementation, especially in large-scale distribution systems with numerous DERs and communication constraints. Balancing the computational demands of the nested optimization with the need for timely decision-making and control actions is crucial to ensure practical applicability and scalability of the approach.

Can the proposed approach be further enhanced to address other distribution system management objectives, such as congestion management or energy loss minimization, in addition to voltage regulation

The proposed nested feedback optimization approach can be further enhanced to address other distribution system management objectives, such as congestion management or energy loss minimization, in addition to voltage regulation. To incorporate these additional objectives, the objective function of the optimization algorithm can be extended to include terms related to congestion relief or energy loss reduction.
For congestion management, the optimization algorithm can be augmented to consider line flow constraints and network capacity limits. By incorporating congestion-related costs or penalties in the objective function, the nested feedback optimization approach can dynamically adjust DER setpoints to alleviate congestion hotspots and improve overall network performance.
Similarly, to minimize energy losses in the distribution system, the optimization algorithm can optimize DER reactive power injections to reduce resistive losses and improve system efficiency. By including loss minimization objectives and constraints in the optimization framework, the nested feedback approach can simultaneously address voltage regulation, congestion management, and energy loss reduction goals.
By integrating these additional management objectives into the nested feedback optimization framework, distribution system operators can achieve a more comprehensive and holistic approach to real-time control and optimization, optimizing system performance across multiple criteria simultaneously.