The transition from bulk and dispatchable generation to renewable and storage systems is revolutionizing and challenging the grid. The inertia deficiency because of renewable energy sources (RESs) penetration poses some stability issues. This structural change is associated with the progress in the technology and control of intermediate power converters, leading to the introduction of grid-forming converters (GFMCs). Future power systems will undoubtedly include a considerable share of GFMCs due to the steadily increasing demand for integration of RESs. This structural change will lead to a transformation in the system operation paradigms, necessitating a deep knowledge of these new devices. In interplay with the power system, this review aims to bridge this gap by surveying the previous research to categorize and discuss the main issues related to the GFMCs. Accordingly, it reviews the stability concepts, key features, and differences in the conventional and emerging low inertia environments. Then, various definitions of the GFMCs and differences regarding the grid- following counterparts are provided. Subsequently, two classifications are presented based on the interfaced resource and the connected grid. Finally, the GFMCs control techniques and pilot projects are explained. The provided information constitutes a roadmap for future studies by presenting, describing, and classifying state-of- the-art research.
