Proceedings of the PowerUp Conference

With the large-scale grid integration of inverter- based resources (IBRs), power systems are rapidly transitioning toward a converter-dominated paradigm. This trend motivates hybrid grid-following (GFL) and grid-forming (GFM) control to combine fast power regulation with improved voltage and frequency support. This paper reviews classical GFL-GFM foun- dations and provides a structured taxonomy of hybrid GFL-GFM strategies for both converters and systems, including switching- type, dual-source, loop-augmented, and system-level categories. A parallel-branch hybrid architecture, which was recently ap- proved by the Western Electricity Coordinating Council, is then introduced. In this model, the GFL and GFM branches operate concurrently under a coordinating plant controller. Both the REGFM C1 converter control model and the REPCGFM C1 plant control model have been implemented and made available in the open-source ANDES simulator. Case studies on Single- Machine Infinite-Bus system and the IEEE 14-bus system validate the effectiveness of the implementation by demonstrating rapid reference tracking and effective voltage and reactive power responses to disturbances.