Passivity and Injection Current Quality Enhancement for Single Inverter-Side Current Feedback <i>LCL</i>-Type Grid-Following Inverters

Single inverter-side current feedback (ICF) LCL-type grid-following inverters (GFLIs) have gained popularity in industrial applications owing to their convenience in over-current protection and economy. They, however, suffer from poor injection current quality in the presence of distorted grid voltage conditions and the risk of oscillation when the variation of the grid impedance pushes the system resonant frequency beyond <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{s}$ </tex-math></inline-formula>/6. To this end, this article presents a virtual grid-side current control (VGCC) scheme with only a single ICF and a repetitive controller (RC) to improve the quality of injection current to comply with the grid code. In the proposed scheme, a differentiator is applied to obtain the capacitor current to construct the virtual grid-side current, and capacitor voltage feedforward active damping (CVF-AD) is also applied to facilitate the output admittance reshaping. Controller parameters are tuned under passivity constraints on the output admittance of the GFLI. With the proposed scheme and parameter design guidelines, both high injection current quality and the approaching Nyquist frequency stable region for single ICF LCL-type GFLIs are simultaneously achieved without introducing any extra hardware costs. Finally, the effectiveness of the proposed scheme is verified by experimental results.