Unified Inertia Modelling and Quantitative Comparative Analysis between Grid-Following and Grid-Forming Converters

Grid-following (GFL) and grid-forming (GFM) converters with inertia control are essential ways to address the ‘low-inertia’ system problem. However, due to the different structures of the two converters, their inertia response performance is hard to evaluate. Several studies have attempted to compare them through simulation, but the absence of a unified and quantifiable inertia metric makes it difficult to get a fundamental comparison. To tackle this issue, the magnitude-phase motion equations for the two converters are derived in this paper, with the dynamic behaviors of multiple control loops considered. The structure of the swing equation is utilized to provide a unified description, and the extracted equivalent inertia is used to express their inertia characteristics quantitatively. Finally, the performance of the two converters is compared by simulation based on equivalent inertia.