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° 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.