Stability assessment considering multi-timescale power system dynamics: Insights into Hopf bifurcations with GFL and GFM IBRs

Real power systems exhibit dynamics that evolve across a wide range of timescales, from very fast to very slow phenomena. Historically, incorporating these wide-ranging dynamics into a single model has been impractical. As a result, power engineers rely on timescale decomposition to simplify models. When evaluating fast phenomena, slow dynamics are often neglected (assumed constant), and vice versa. This paper underscores the limitations of this traditional approach by demonstrating the importance of assessing power system stability while considering multiple timescales simultaneously. Using the concept of Hopf bifurcations, the study illustrates instability issues that would be missed if multi-timescale dynamics are not considered. Specifically, it exemplifies a class of instability that is overlooked when multi-timescale dynamics are decoupled, with a particular emphasis on networks featuring inverter-based resources.