To keep the grid stable and reliable, grid-forming (GFM) characteristics of synchronous generators are also demanded from inverter-based resources (IBRs). A synchronous machine with rotating mass and helped by its governor and exciter to keep the voltage and frequency stable and provide the short circuit currents. This comes naturally to the machine as per the laws of physics. The performance of inverter-based devices on the other hand predominantly relies on the embedded control functions. On top of that, based on the operating conditions or the physical limitation of the source or the inverters, the availability of instantaneous energy reserve and short circuit contribution may not be guaranteed.

This paper provides a detailed evaluation of the capabilities of different power-electronic based assets in the grid to provide grid-forming characteristics. Battery energy storage system (BESS) presents the pioneering technology in introducing GFM control on a broader scale in the power system. The requirement of an available energy buffer for GFM control adaptation provides BESS with an inherent advantage compared to other IBRs like wind and solar and assets like STATCOMs and HVDC converter systems. For example, GFM control of wind turbines is more difficult when compared to BESS due to the required coupling of the turbine aerodynamics and the converter control. Standalone PV systems without BESS face a fundamental disadvantage in grid-forming applications due to their lack of intrinsic inertia. In the case of STATCOMs the GFM control can be implemented with or without energy storage with an impact on the STATCOM’s ability to provide active power control network. HVDC systems may also provide certain GFM capabilities limited by their energy reserve made available by different means.

After discussing the GFM related capabilities of different assets, an evaluation of these capabilities in terms of requirements as laid down by different regulators in different regions of the world is presented.