Parameter Estimation and Grid Synchronization Using a First-Order Frequency-Locked Loop

Fast and accurate estimation of frequency, phase angle, and amplitude are necessary for seamless synchronization of grid-connected converters. Therefore, this article proposes a first-order frequency-locked loop (FLL) structure for single-phase grid applications. The proposed FLL relies on signals generated from a first-order integrator orthogonal signal generator (OSG). With this approach, the generated signals exhibit a semi-quadrature phase angle offset with respect to the single-phase input voltage. Thus, unlike in existing FLLs where a 90 degrees phase delay is introduced in the input signal, delay introduced using the proposed approach is halved. More so, the other orthogonal signal in the proposed approach exhibits a leading phase angle with respect to the single-phase input voltage. These distinctions assist the proposed FLL in achieving improved transient performance. A linearized model of the FLL is obtained where it is shown that the proposed FLL realizes a type-1 control system, giving it the ability to track step changes in the input voltage's frequency with zero steady-state phase angle error. Extension of the proposed FLL for applications involving disturbances such as harmonics, dc-offset, and noise is also presented. Experimental results are provided to evaluate the performance of the proposed FLL in comparison with other FLL-based schemes where it is shown that the proposed FLL offers advantages such as simplicity, fast response, and minimum deviation in its frequency, phase angle, and amplitude estimations.

Automated summary

This article proposes a first-order frequency-locked loop (FLL) structure for single-phase grid applications, which can estimate the frequency, phase angle, and amplitude fast and accurately. Experimental results show that the proposed FLL offers advantages such as simplicity, fast response, and minimum deviation in its frequency, phase angle, and amplitude estimations.