Multi-Area Architecture for Real-Time Feedback-Based Optimization of Distribution Grids

Abstract

The transition to a more environmentally-friendly power system, predominantly driven by Distributed Energy Resources (DERs) such as smart loads, Electric Vehicles (EVs), and Photovoltaics (PVs) systems, signals a shift towards a new structural paradigm. Significant challenges have emerged as more DERs, particularly those interfaced through inverters, are integrated into the grid. These challenges include variability in power supply and reduced rotational inertia, which contribute to more frequent frequency events and grid instabilities globally. Despite these challenges, DERs offer potential solutions by participating in ancillary service provision.

This thesis aims to harness the potential of DERs at the distribution network (DN) as their integration increases. We focus on overcoming coordination challenges between distribution and transmission networks to integrate DN-DERs in frequency support. To achieve this goal, we develop a coordination framework for distribution networks to manage the DERs. Subsequently, we integrate this DN framework with a recently proposed fast frequency control scheme at the transmission network (TN) level.

In the first stage, we develop a hierarchical feedback-based control architecture for DN-DER coordination. This architecture enables DNs to swiftly respond to power set-point requests from the Transmission System Operator (TSO) while adhering to local operational constraints and ensuring data privacy. The scheme minimizes inter-area communication needs by leveraging physically adjacent areas within the DN control hierarchy. Rigorous stability analysis establishes intuitive closed-loop stability conditions, accompanied by detailed tuning recommendations. Case studies on multiple feeders, including IEEE-123 and IEEE-8500, validate the architecture using a custom MATLAB®-based application integrated with OpenDSS©. Results demonstrate scalability and effective coordination of DERs in response to TSO commands while managing local DN disturbances and operational limits.

In the second stage, we integrate the developed DN control framework into a TN fast frequency control scheme by incorporating a simplified linear model of DN dynamics into the TN control design framework. This integrated approach aims to enhance system responsiveness and performance. To validate this approach, we conducted case studies using the IEEE 9-bus TN system, incorporating IEEE-123 DNs structured according to the hierarchical control framework developed in stage 1. The TN controller, designed with the integrated DN dynamic model, demonstrated improved performance across various DN feeder configurations and tuning scenarios.

Combining these stages yields a comprehensive solution that enhances overall system stability and performance. By optimally utilizing DN-DERs to respond to the TN controller, which is designed with awareness of DN-DERs dynamics, the integrated solution resulted in improved response times and reduced oscillations.