Enhanced stability of grid-connected inverter using adaptive filtering damping of capacitive current feedback of LCL filter

LCL filters are commonly used in voltage source inverters (VSI) for their low cost and effective harmonic reduction. However, resonance frequencies above one-sixth of the sampling frequency pose significant stability challenges in grid-tied LCL-VSIs. This study introduces an adaptive high-pass filter (HPF) as a compensator in capacitor current feedback (CCF) for active damping to enhance stability. The circle search algorithm is utilized to design optimal gain and crossover frequency for the HPF, along with gains for the proportional-resonant controller. The affine projection mixed-norm algorithm is employed to dynamically adjust the HPF gain in response to varying grid conditions. Extensive simulations are carried out in MATLAB/SIMULINK and the real-time Typhoon HIL simulator, validating the proposed HPF-CCF. Results demonstrate improved performance under significant variations, including up to 300% fluctuations on both the inverter and grid sides, as well as variations in reference current. Introducing this damper increases the LCL filter resonance to one-fourth of the sampling frequency, substantially above the critical frequency region of one-sixth of the sampling frequency. Compared to conventional CCF-based control, the self-tuned HPF-CCF significantly enhances stability at high resonance frequencies, expanding the damping region of CCF-based control and increasing the adaptability of the LCL-VSI system to changing grid conditions.