A Discrete-Time Frequency-Locked Loop for Single-Phase Grid Synchronization Under Harmonic Distortion

This article presents a discrete-time frequency-locked-loop (FLL) scheme that estimates the in-phase fundamental component of a distorted single-phase reference signal and its fundamental angular frequency. The proposed scheme also estimates the square-phase fundamental component as a set of orthogonal signals. The proposed design is based on an exact discrete model of a single-phase signal generator. It is shown that the proposed method provides an accurate response even under low sampling frequency. The proposed scheme includes, as a plug-in block, an explicit harmonic compensation mechanism to reduce the effect of harmonic distortion. The article includes a local stability analysis for the proposed scheme as well as guidelines for control parameter tuning. Experimental results are provided to assess the performance of the proposed scheme under angular frequency variations and harmonic distortion on the reference signal.