Highly-Scalable Transmission and Distribution Dynamic Co-Simulation With 10,000+ Grid-Following and Grid-Forming Inverters

The inverter-based resource (IBR) has been an important component of power generation within both transmission and distribution systems. The impacts of high IBR penetration on system transient stability have not been explored extensively due to the lack of high-fidelity power grid and inverter models. The aggregate IBR model in the transmission system is only suitable for representing bulk power system (BPS)-connected IBRs, and it cannot precisely reproduce the dynamics of distributed IBRs in the distribution system due to its oversimplified structure. In this study, we have developed a high-penetration fully-connected transmission and distribution (T&D) co-simulation platform that supports the dynamic co-simulation of a synthetic mini-WECC transmission system with multiple IEEE 8500-node distribution systems. The entire platform can accommodate 10,000+ dispersed and 40+ BPS-connected IBRs and achieve 100% power generation from IBRs. A novel iterative T&D power flow initialization technique was proposed to maintain stable transition from power flow to dynamic co-simulation mode with high penetration of IBR models. This study explores the impacts of grid-forming (GFM) and grid-following (GFL) inverter control on the dynamics of large-scale T&D network. Moreover, a co-simulation platform was developed and tested using high-performance computing (HPC) resources to facilitate parallel simulation.