Comparing Time-Domain Simulation Methods for Systems With Heterogeneous Generation
Fiona Majeau, University of Colorado Boulder
Inverter-based resources (IBRs) such as wind, solar, and batteries are gaining a significant presence on the electric grid alongside traditional synchronous generator resources (SGRs) such as coal and nuclear. One important difference between these two resource categories is the timescale of their dynamic behavior. IBRs are dominated by electromagnetic phenomena, which are faster than the electromechanical phenomena of SGRs. The disparate timescales introduced by this heterogeneous generation mix affect the dynamic behavior and stability of the grid. One common tool for assessing grid stability is a time-domain simulation. This process consists of modeling the grid with differential equations, defining a potential disturbance, and implementing a time-integration method to solve for the trajectory of the system states. There are several commercial software tools available for such modeling and time-integration analysis, but they are tailored toward systems dominated by either electromechanical or electromagnetic timescales, not systems with both. Timescale separation within a system of differential equations, often called stiffness, is a highly relevant characteristic when selecting a time-integration method. Thus, it is reasonable to investigate what methods may be appropriate for systems with heterogeneous generation. This work explores the performance of different time-integration methods as a function of generation heterogeneity, focusing on methods that are appropriate for stiff systems with disparate timescales. All simulations use a nine-bus network model with three SGRs and three IBRs. The heterogeneity is introduced by varying the ratio of SGR and IBR power injections throughout the system.