Robust Grid-Following Control with Active Delay Compensation in Weak Grid

This paper proposes a grid-following-based, robust delay compensation control approach that effectively mitigates the effects of digital delay. The approach is especially suitable for stabilizing LCL-type grid-connected converters in weak grids with time-variant impedance. Analytical studies reveal the negative damping characteristics associated with digital delay, and mathematical proofs analyze the potential harmonic oscillations triggered by digital delay. Based on these results, a revised active damping method with delay compensation is designed via capacitor-current feedback for resonance suppression. With optimization, expected output impedance was achieved, eliminating the adverse effects of time delay and drastically improving converter stability. Additionally, robustness against time-varying grid impedance can be realized in weak grids. Finally, the proposed delay compensation method was verified through experimental results.