Design of Digital Filter-based Highly Robust Active Damping for LCL-filtered Grid-tied Inverters

Damping is required in grid-connected LCL-filtered inverters. Due to additional power losses caused by passive elements, active damping is more favorable. As an active damping solution, the single-loop filter-based damping, being directly plugged into the current controller, features no extra sensors and simplicity, and thus it has drawn much attention in LCL-filtered inverters. However, the existing filter-based damping is not very satisfactory because of limited frequency characteristics. For example, the notch filter designed for a low LCL-resonance frequency does not function well for a high resonance frequency owing to its overmuch phase lead, which means that one filter is not sufficient to cover all possible LCL resonance frequencies caused by parameter drifts, indicating unnecessary repetitive designs and poor universality. Thus, this paper proposes a notch-like digital filter-based single-loop active damping method, which covers a wide range of frequencies up to the Nyquist frequency. That is, the proposed is robust against LCL filter parameter drifts and grid impedance variations. Simulation results verify the proposed method.