Transient stability analysis of power systems containing grid-following inverters
File(s)
Author(s)
Zhang, Yifan
Type
Thesis
Abstract
Electric power systems are undergoing a fundamental transition from synchronous generator (SG)-dominated systems to inverter-based resource (IBR)-dominated systems. Grid-following (GFL) inverters are widely deployed as interfaces for renewable generation. The large-signal stability properties of IBRs differ substantially from SGs. More importantly, the stability assessment tools that have served well in SG-dominated systems, such as the equal-area criterion and global energy functions, cannot be directly applied to IBR-dominated grids. This thesis tackles three key stability questions: (i) how might energy function methods be adapted for use in IBR grids, (ii) how can large-signal stability of mixtures of GFL and GFM inverters be analyzed, and (iii) how can models of IBR with multiple nest control loops be simplified for analysis. First, the large-signal stability of PLLs is investigated in depth using both manifold theory and energy functions. A new energy function tailored for proportional–integral controllers is proposed. Second, this thesis elucidates the interaction mechanisms among heterogeneous inverters—including GFL, grid-forming (GFM), and grid-supporting (GSP) types. It is proven that no energy function exists for such systems. To overcome this barrier, a manifold theory is employed to accurately determine the region of attraction (ROA). To address the computational complexity, reduced-order models of the inverter are used. The metric - stability radius (SR) - is defined to evaluate the large-signal stability margin. Third, to analyze the large-signal coupling between PLL and outer control loops such as DC-link voltage control (DVC) and terminal voltage control, an asymptotic analysis approach, termed the bandwidth separation method, is proposed. Through this method, it is revealed that there is a tradeoff between phase-angle stability and DC-link stability in PLL–DVC bandwidth configuration. Optimal bandwidth configurations are identified under various grid fault conditions. Power hardware-in-the-loop and control hardware-in-the-loop experiment platforms are built and used to validate all theoretical analyses.
Version
Open Access
Date Issued
2025-10-02
Date Awarded
2026-04-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Green, Timothy
Publisher Department
Department of Electrical and Electronic Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)