PNNL

Abstract

Traditional dynamic models of inverter-based DERs are mostly electromagnetic models and positive-sequence electromechanical models, neither of which is suitable for simulation of large-scale, three-phase unbalanced distribution systems. This paper develops three-phase, electromechanical models for both grid-forming and grid-following inverters, and integrates them into a three-phase unbalanced distribution network solver, enabling transient stability simulation of large-scale distribution systems with high penetration of inverter-based DERs. The proposed inverter models are validated against electromagnetic simulations and field test data from the CERTS/AEP microgrid testbed, and simulated in an islanded 5,252 node distribution system in the GridLAB-D simulation environment. Simulation verifies the effectiveness of the proposed models for large-scale distribution systems. Results show that compared to grid-following inverters, the high penetration of grid-forming inverters can significantly improve the voltage and frequency transient stability of distribution systems.