An Enhanced Adaptive Frequency-Locked Loop Based on Fixed-Length Transfer Delay

The fixed-length transfer delay-based adaptive frequency-locked loop (TD-AFLL) has drawn much attention with concise structure and faster response speed compared with the conventional second-order generalized integrator-based FLL. However, the application of TD-AFLL is still limited due to the poor performance in terms of phase-angle detection under distorted grid conditions. This letter proposes an enhanced TD-AFLL (ETD-AFLL) with high phase-angle detection accuracy under distorted grid conditions. The ETD-AFLL employs a filter in parallel with the FLL rather than using a pre-filer before the FLL, so that the constructed phase-angle detection keeps a fast response speed. In addition, this filter fully utilizes the inherent samples of TD-AFLL, thus it requires the slightly additional computational cost. Experimental results are given to support the proposed ETD-AFLL.