Wide Area Control and Monitoring for Low-Inertia Power Systems

Abstract

Economic dispatch (ED) of inverter-based distributed energy generators (DGs) enhances profitability in utility-based microgrids. While droop control enables ED without requiring communication, its lack of inertia results in excessive rates of change of frequency (RoCoF) following disturbances, posing significant stability risks. Virtual synchronous generators (VSGs) offer a promising solution by introducing virtual inertia to improve frequency stability and mitigate RoCoF. This thesis proposes a combined ED and VSG framework (ED-VSG) to minimize generation costs while enhancing inertia support. However, due to its low-pass filter structure, the ED-VSG model exhibits stability limitations. To address this, enhanced ED-VSG models are developed to improve system stability. Despite these improvements, replicating the swing equation in VSGs induces low-frequency oscillations (LFOs), which can degrade system performance. To suppress LFOs and enhance the damping ratio without compromising the permissible grid-forming operating frequency, this thesis introduces a novel damping method. While these advancements improve system dynamics, the inherent primary control structure leads to persistent frequency deviations, necessitating secondary frequency regulation. Existing decentralized methods can correct these deviations but fail to maintain ED. To overcome this limitation, this research proposes a practical control framework based on integral controllers that restores frequency while ensuring ED. Additionally, a dynamic reactive power control loop is introduced to enhance stability while preserving VSGs' dynamic characteristics. Despite achieving frequency restoration, the proposed model encounters a limited inertia provision. High inertia improves RoCoF mitigation but exacerbates power oscillations, reducing effectiveness. To address this, a modified control framework is developed, employing a two-stage filtration approach. This approach reduces RoCoF without increasing inertia gain and effectively decouples ED nonlinearity from the microgrid's frequency dynamics. Comprehensive small-signal stability analyses validate the proposed stability improvements. Furthermore, extensive time-domain simulations, sensitivity analyses, lab-scale microgrid experiments, and real-time control-in-the-loop simulations confirm the effectiveness of the proposed controllers.

Date of Award	7 May 2025
Original language	American English
Supervisor	Ahmed Al Durra (Supervisor)