Digital Low-Pass-Filter-Based Single-Loop Damping For Lcl-Filtered Grid-Tied Inverters

Damping the LCL-filter resonance is an essential issue for grid-connected inverters. In most of the prior-art solutions, active damping focuses on a dual-loop architecture, e.g., using the capacitor-current to damp the resonance, thus complicating the entire control loop and/or increasing the cost. Digital filters (such as notch and all-pass filters) directly cascaded into the current controller, referred to as a single-loop scheme, are thus more economical, which feature no extra sensors and a simple open-loop scheme with easy parameter tuning. This paper proposes a practical single-loop damping method for grid-current feedback control (GCF) based on a first-order digital low-pass filter, which realizes damping by lagging the phase and meanwhile reducing the magnitude response for a sufficient gain margin. Simulations verify the proposed method.