Robust Grid-Current-Feedback Resonance Suppression Method for LCL-Type Grid-Connected Inverter Connected to Weak Grid

In this paper, a robust grid-current-feedback resonance suppression (GCFRS) method for LCL-type grid-connected inverters is proposed to enhance system damping without introducing switching noise and eliminating the impact of control delays on system robustness against grid-impedance variation. It is composed of the GCFRS method, the full duty-ratio and zero-beat-lag pulsewidth modulation (PWM) method, and the lead-GCFRS (LGCFRS) method. First, the GCFRS is used to suppress the LCL-resonant peak well and avoid introducing switching noise. Second, the proposed full duty-ratio and zero-beat-lag PWM method is used to eliminate the one-beat-lag computation delay without introducing duty cycle limitations. Moreover, it can also realize the smooth switching from positive to negative half wave of the grid current and improve the waveform quality. Third, the proposed LGCFRS is used to further minimize the control delay and make the positive or negative critical frequency of its virtual equivalent damping resistance increase above 0.5 switching frequency. Then, the system's robustness and dynamic performance can be greatly improved. Finally, the experimental results confirm the theoretical expectations and the effectiveness of the proposed method.