A Dynamic Similarity Index for Assessing Voltage Source Behaviour in Power Systems

Due to the fundamental transition to a power electronic dominated power system, the increasing diversity of dynamic elements underscores the need to assess their similarity to mature electrical engineering models. This article addresses the concept of the Dynamic Similarity Index (DSI) for its use in power electronics-dominated networks. The DSI is a multi-purpose tool developed to be used by different stakeholders (e.g., converter manufacturers and system operators). This index is calculated per frequency, which serves to anticipate potential differences in particular frequency ranges of interest between the model under study and a reference model. Within the scope of this study, the dynamic similarity of inverter-based generators and clusters of network components to an ideal voltage source behind an impedance is assessed, due to the relevance of this fundamental circuit in the representation of generation units in power system studies. The article presents two potential applications based on this mathematical framework. First, for manufacturers to evaluate control performance compared to a reference model and second, for operators to diagnose buses with voltage vulnerability based on a user-defined reference Short-Circuit Ratio (SCR) value. The DSI results for these two case studies are validated using Matlab Simulink simulations.