The three-phase synchronous reference frame phase-locked loop (3-SRF-PLL) is widely used in three-phase power electronics and power system applications thanks to its desirable performance and its simple yet robust structure. Inspired from the 3-SRF-PLL and due to the increasing interest in single-phase applications, multiple single-phase SRF-PLL (1-SRF-PLL) versions have also been proposed in the recent years. This paper presents a unifying approach to the understanding and analysis of the 1 -SRF-PLLs. This paper integrates several 1 -SRF-PLLs having apparently different structures into a single structure. The approach is much useful in understanding various PLLs and also in facilitating further developments in this field.