Improvement of the Interface Models of a Per-Phase Phasor/EMT Co-Simulation Platform for Studying Transients and Dynamics in Distribution Grids With IBRs

Co-simulation offers a time-efficient method for accurately analyzing the behavior of distribution systems dominated by inverter-based resources (IBRs). However, most co-simulation studies in the literature overlook distribution grids. Additionally, these studies do not discuss practical IBR models nor how to initialize the interface model variables of co-simulation platforms. To obtain co-simulation results that are reasonably accurate for distribution system-based planning and operation, it is pertinent to develop co-simulation platforms well-suited for studying the accurate behavior of IBRs coupled to unbalanced distribution grids. This paper introduces an initialization algorithm for initializing the interface model variables of co-simulation platforms. The initialization algorithm is anchored on leveraging the fast execution speed of the per-phase phasor simulation to quickly pre-calculate initial values of interface model variables prior to starting co-simulation. This paper further proposes the inclusion of rate limiters in the co-simulation platform’s interface models to prevent the incapability of the per-phase phasor simulator to clear faults at zero-crossing of currents from falsely impacting the control system of practical IBR models. The proposed methods are validated by benchmarking the results from a per-phase phasor/electromagnetic transient (EMT) co-simulation of an IBRs-dominated IEEE 34-Node test feeder against the results from a full EMT simulation.