Modeling and Tuning of Circular Limit Cycle Oscillator FLL With Preloop Filter

Circular limit cycle oscillator-frequency-locked loop (CLO-FLL) is a recently proposed advanced nonlinear technique for the parameter estimation of grid voltage signal. It has fast convergence and can handle dc bias/offset. Nevertheless, the performance degrades in the presence of harmonics. In this letter, we propose the application of preloop filtering to enhance the robustness of the CLO-FLL in the presence of harmonics. Preloop filtering slightly increases the computational complexity. However, number of parameters to tune remain the same. The small-signal modeling, tuning, and performance comparisons of both techniques are performed in this letter.