Review of Testing and Validation Methodologies for Grid-Forming Performance of Inverter-Based Resources

With the rapid integration of renewable energy sources, inverter-based resources (IBRs), including wind power plants, photovoltaic systems, battery energy storage systems, and high-voltage direct-current converters, are progressively displacing conventional synchronous generation. This transition changes the dynamic behaviour and stability characteristics of power systems, making grid-forming (GFM) control an important technology for secure operation under high IBR penetration. This paper reviews the functional requirements, application contexts, standards, testing methodologies, and validation criteria for GFM IBRs. Key GFM capabilities, including voltage-source behaviour, frequency and voltage support, fault ride-through, weak-grid operation, islanding, black start, and interoperability, are examined across grid scales ranging from microgrids to transmission, offshore wind, HVDC, and interconnected systems. Testing approaches are compared in a structured manner, including RMS and electromagnetic-transient simulation, real-time digital simulation, controller and power hardware-in-the-loop testing, laboratory testing, field demonstration, co-simulation, and model validation. Representative test scenarios and performance indicators are linked to these functional requirements. The review further synthesises an industry-oriented set of tests and validation procedures for GFM IBRs, illustrated through the verification needs of GFM energy storage systems. The review also identifies the continuing challenges in model fidelity, current and energy limitations, scalability, multi-vendor interactions, and harmonisation of test procedures and acceptance criteria, and highlights priorities for standardised benchmarks, interoperability testing, and coordinated plant- and system-level validation.