The role of grid-forming inverters in enabling high penetration of renewable energy in power systems: standards, ancillary services, current deployment, and future perspectives

As the global energy landscape undergoes a significant transformation toward increased integration of renewable energy sources (RESs), the stability and resilience of power systems face new challenges. Traditional grid stability mechanisms, heavily reliant on synchronous generators, are becoming less effective in systems with high-RES penetration. Grid-forming inverters (GFMIs) have emerged as a crucial technology to address these challenges by enabling inverter-based resources to not only inject power into the grid but also support critical grid functions, such as frequency and voltage regulation. While most literature focuses on GFMI control strategies, a critical gap remains in the understanding of their ancillary services, emerging standards, and real-world deployment. This paper provides a holistic review to bridge this gap, synthesizing the state of the art in GFMI ancillary services, international standards, grid codes, and global pilot projects. This review confirms that GFMIs are essential for providing a wide range of ancillary services beyond simple voltage and frequency regulation. It further demonstrates that although standards are emerging worldwide, they remain insufficiently harmonized, and it systematically identifies the key technical features and validated outcomes of leading real-world deployments. The findings indicate a critical need for updated market mechanisms and regulatory frameworks to fully realize the potential of GFMIs and ensure a stable transition to a power system dominated by renewable energy. Finally, the paper highlights future developments, challenges, and recommendations based on a thorough review of existing literature and real-world case studies.