Most of the inverter-based energy sources installed across the world today use phase-locked loops (PLLs), which depend on externally generated voltages from synchronous machines for their operation. These inverters are classified as grid-following converters, and they currently dominate the IBR fleet in power systems across the world. If there is any distortion in the grid voltage due to some power system disturbance like transmission line fault, generation or load loss, these inverters may lose synchronism and cease to transfer power. Hence, its capabilities are limited due to its heavy reliance on a stable grid reference for stable operation. There is no inherent inertia contribution from the grid following inverter-based resources. However, inertia is an important parameter in the operation of the power grid. The inertia holds the system frequency during a generation/load loss event. This limitation makes the grid-following converters insufficient to meet system needs.

There has been a surge in research activities in academia and industry to explore how IBRs can maintain system security and stability in grids with low inertia. If some of the IBR-based units can emulate the performance of synchronous machines, then the stability of IBR dominated grid will improve. The grid-forming converter, which emulates the synchronous generator, is the subject of ongoing study in this area and has emerged as the most promising solution to these challenges. However, they are still in the early stages of development. It has been demonstrated that a grid-forming inverter, when combined with a reliable energy source, can provide essential system services to some extent, including inertia and system strength equivalents.

Major research aspects in this domain include.

[1]	Grid-forming control of inverter-based resources
[2]	Integration of battery storage with grid for frequency control and to provide inertia.