Impact of Grid-Forming Devices on Voltage Support Strength in High-Penetration Renewable Energy Systems

Grid-forming (GFM) control strategies allow power electronic devices to mimic synchronous generator characteristics, offering voltage support during system disturbances by actively adjusting their states. Integration of GFM devices alters the system's voltage support strength, but suitable quantitative assessment methods are still lacking. This paper focuses on developing and investigating quantitative indicators that can assess the voltage support strength in power systems after the integration of GFM devices. These indicators are crucial for understanding how GFM devices influence system stability, particularly in high-penetration converter-interfaced renewable generation (CRE) systems. First, we propose a current-limiting impedance model for GFM devices, which effectively characterizes their voltage support capability under currentlimiting conditions. Building on the multiple renewable shortcircuit ratio (MRSCR) as a foundational parameter, we develop a unified and comprehensive metric for assessing voltage support strength across a wide range of operational scenarios. This metric can be employed to evaluate the impact of various factors, including CRE penetration, system configuration, and GFM device characteristics. The computational method is demonstrated through a practical example, simplifying large-scale grid computations and providing a clear methodology for evaluating voltage support strength in high-penetration renewable energy systems. By reducing the complexity of these calculations, the method enables more efficient analysis of grid stability and helps optimize system design and operation.