Single-phase frequency-locked loops: A comprehensive review

Synchronization techniques can be classified into open-loop and closed-loop methods. In power and energy applications, which are the focus here, the latter type is more popular. Phase-locked loops (PLLs) and frequency-locked loops (FLLs) are two broad categories of closed-loop synchronization techniques. The aim of this paper is providing a review of recent advances in designing single-phase FLLs, which can be very useful for both researchers and engineers. The historical development of a standard single-phase FLL, its modeling and tuning aspects, its relationship with adaptive notch filters, its advanced versions for the synchronization purposes under adverse grid conditions, its modification for different industrial applications, its connection with single-phase PLLs, and its discretization aspects are the main parts of this review.