With the increasing penetration of renewable energy sources

the strength of AC grids gradually weakens. Enhanced interactions between weak grids and inverter-interfaced distributed generators (IIDGs) break the independence of equivalent sequence networks

leading to coupling among system sequence components. Traditional fault current equivalence models for IIDGs exhibit errors in such scenarios. This paper first analyzes the limitations of conventional IIDG equivalence models in weak AC systems

revealing that persistent steady-state errors in the PLL lead to sequence-component coupling in the IIDG output under weak grid conditions. An IIDG sequence component coupling fault equivalence model is subsequently developed

incorporating machine-grid interactions

including PLL dynamics

control loops

and transmission line characteristics. Simulation results validate the superiority of the proposed sequence component coupling model over traditional approaches

the impacts of grid strength and PLL response speed on coupling severity. A power hardware-in-loop (PHIL) experiment further verifies the model's accuracy. The research outcomes enhance the precision of fault current calculations in power systems and improve operational reliability.