Comparative Analysis of Impedance-Based and Eigenvalue-Based Approaches for Stability Assessment

Various methods for assessing the stability of power systems and components are available, with the most prominent small-signal techniques being eigenvalue-based and impedance-based approaches. Each method offers specific advantages and faces inherent limitations. This paper examines a small Direct Current (DC) grid and compares the applicability, accuracy, and key differences between these two stability assessment techniques, revealing novel insights regarding the imprecise results of the impedance-based approach. These results are relevant for stability investigations of Alternating Current (AC) and DC grids. As an example, a DC grid with a Dual-Active Bridge (DAB) converter feeding an inductive load via a transmission line modeled as a pi equivalent circuit is considered. The eigenvalue-based approach provides precise insight into the system’s dynamic behavior at a given operating point by calculating participation factors for each state and mode in the system. Conversely, the impedance-based approach exhibits sensitivity to the partitioning of the system into source and load subsystems, which can lead to inaccuracies or misinterpretations. Additionally, the estimation of system impedance is influenced by the operating point, requiring careful analysis. The applicability of these methods to AC grids is also discussed.