Grid-forming (GFM) control is a critical function for grid-connected inverters, especially as the penetration of inverter-based resources (IBRs) continues to rise. A common implementation of GFM control employs a cascaded voltage and current control structure (dual-loop), where the voltage regulator generates a current reference for the inner current loop. Such control schemes are found in various applications, including HVDC and FACTS systems, depending on converter topology and grid code requirements. However, the dynamic interactions between the voltage and current loops in dual-loop GFM control remain insufficiently explored in the literature.

This paper presents a detailed modeling and analysis of the interactions between the voltage and current loops in dual-loop GFM control, with a focus on transient grid conditions such as voltage ride-through and phase jump events. First, various dual-loop control strategies are reviewed, and their dynamic behaviors during grid disturbances are examined using a phasor-based analysis to highlight loop interactions and their effects on grid support and fault ride-through performance. Next, analytical models in the form of transfer functions are developed and validated through numerical simulations. These models are used to compare different dual-loop designs and provide deeper insights into the control dynamics observed in the phasor-based analysis. Finally, based on the developed models, design guidelines and parameter tuning strategies are proposed and validated to enhance GFM performance under grid transients.