Role Determination of Impedance Coupling in GCC With DC-Link Virtual Inertia Control

Virtual inertia control (VIC) allows grid-connected converter (GCC) to emulate inertia via the dc-link capacitance. Yet, such a scheme's stability impact revealed by the impedance perspective is often overlooked, resulting in coupling issues between the converter and the grid. This article presents a comprehensive analysis of the effect of the dc-link's VIC on the GCC system. The GCC's smallsignal impedance model is first proposed, which reveals a strong impedance coupling between the GCC's d-axis and q-axis elements due to VIC and PLL. Subsequently, the method for the role determination of impedance coupling is proposed to investigate the coupling influencing mechanism on the system. It quantifies the impedance coupling effect on the grid's stability margin. This also allows the critical GCC controllers to be separately designed based on the GCC impedance coupling and noncoupling terms. Facing the strong coupling issue, improved VIC is further proposed to weaken the coupling effect and, thus, broaden the range of available control parameters. Numerical and experimental results are presented to verify the theoretical analysis.