A Self-commissioning Notch Filter for Active Damping in a Three-Phase LCL-Filter-Based Grid-Tie Converter

LCL-filters are a cost-effective solution to mitigate harmonic current content in grid-tie converters. In order to avoid stability problems, the resonance frequency of LCL-filters can be damped with active techniques that remove dissipative elements but increase control complexity. A notch filter provides an effective solution, however tuning the filter requires considerable design effort and the variations in the grid impedance limit the LCL-filter robustness. This paper proposes a straightforward tuning procedure for a notch filter self-commissioning. In order to account for the grid inductance variations, the resonance frequency is estimated and later used for tuning the notch filter. An estimation for the maximum value of the proportional gain to excite the resonance is provided. The resonance frequency is calculated using the Goertzel algorithm, which requires little extra computational resources in the existing control processor. The discrete Fourier transform coefficients are therefore obtained, with less calculations than the running sum implementation and less memory requirements than with the fast Fourier transform (FFT). Thus, the self-commissioning technique is robust to grid impedance variations due to its ability to tune the grid-tie inverter on-site. Finally, the analysis is validated with both simulation and experiments.