Grid-Forming (GFM) generation systems are expanding rapidly worldwide, with manufacturers developing solutions that differ according to their technical background, experience in weak or isolated grids, internal control platforms, and project‑specific requirements derived from grid codes. As a result, GFM implementations exhibit heterogeneous dynamic behaviors that grid operators evaluate with varying levels of confidence. Although the benefits of GFM technologies are widely recognized, certain responses during disturbances have raised concerns and highlighted the need for clearer verification procedures and greater transparency from manufacturers.

International experience in grid integration studies shows increasing efforts by manufacturers to refine GFM control schemes, along with emerging regulatory initiatives from system operators. Unlike previous technological transitions, such as the widespread adoption of Grid‑Following (GFL) renewable generation, the shift toward GFM requires detailed EMT (Electromagnetic Transient) studies to accurately assess dynamic performance. The maturity of EMT simulation tools now enables reliable evaluation of these new control paradigms.

One behavior identified in several implementations is the transition from GFM to GFL mode during voltage dips caused by short circuits. Although this is often justified to meet fault‑ride‑through current injection requirements, some operators consider the mode change undesirable due to the loss of expected robustness and inertia‑like response. Consequently, operators such as Fingrid have introduced detailed verification protocols for BESS systems, explicitly rejecting GFM‑to‑GFL transitions during faults as a condition for acceptance.

In other regions, such as Spain, discussions remain focused on defining preferred GFM schemes, while formal certification protocols are still under development. However, incentive mechanisms for BESS (Battery Energy Storage Systems) projects providing black‑start capability are already driving practical testing of systems that must start in island mode and synchronize with very weak grids. These commissioning‑type tests are encouraging hybrid plants to adopt more reliable GFM functionalities.

Australia, a long‑standing reference in renewable integration requirements, published new GFM technical guidelines in 2025. Industry feedback has been broadly positive, as the proposed scheme is simple, closely aligned with synchronous‑machine behavior, and suitable for large‑scale deployment. This synthesis results from extensive comparative analyses by operators, research institutions, and distribution companies, evaluating manufacturer proposals under a wide range of dynamic scenarios.

The paper will present an overview of current GFM solutions from leading manufacturers of wind, solar, and BESS systems, highlighting their main characteristics and control approaches. It will also analyze operator testing protocols in different countries, identifying critical behaviors that may lead to acceptance or rejection of GFM proposals. The study aims to support the development of clearer criteria for robust and interoperable GFM deployment in future power systems.