Advanced single-phase SOGI-FLL using self-tuning gain based on fuzzy logic

In this paper, a frequency-locked loop (FLL) algorithm using the self-tuning gain is proposed for a precise phase angle detection from a second-order generalized integrator (SOGI) in a single-phase AC system. The integrator gain in the FLL is tuned by the fuzzy logic controller in which the frequency error and its variation are adopted as control input variables. In this method, the nonlinear characteristic of the frequency error to the variation of the central frequency is compensated by the self-tuning gain. With the proposed algorithm, the performance of the SOGI-FLL is much improved at the grid faults. The simulation and experimental results have verified the validity of the proposed method.