Stability Criterion Based on Gain-Phase Mix for Multi-Converter Systems

This paper proposes a gain-phase mixed stability criterion based on the small gain theorem and small phase theorem to analyze the small-signal stability of grid-following converters (GFL) and grid-forming converters (GFM) in an open-loop decentralized manner. Compared to traditional methods such as eigenvalue analysis and impedance-based analysis, this approach offers improved scalability and reduced conservatism, particularly in high-frequency ranges. By integrating gain and phase conditions, the method provides a more accurate and flexible framework for assessing the stability of both single-converter and multi-converter systems. The study highlights the advantages of grid-forming converters in enhancing grid strength and maintaining system stability, while also addressing the limitations of grid-following converters in meeting gain stability conditions. The method analyzes the closed-loop system in an open-loop decentralized manner, offering better scalability and conservatism. The paper first establishes a small-signal model for multi-converter gridconnected systems, derives the system's admittance matrix, and presents stability criteria based on gain and phase. Theoretical analysis and time-domain simulations validate the effectiveness of the proposed criterion.