An Enhanced Frequency-Adaptive Single-Phase Grid Synchronization Technique

Second-order generalized integrator phase-locked loop (SOGIPLL) relies on the frequency feedback from the PLL estimation. The frequency is used to generate the equivalent in-phase and in-quadrature signals of the single-phase grid voltage. The phase-angle-coupled frequency feedback makes the SOGIPLL structure vulnerable to various grid voltage transients such as voltage sag, phase-angle jumps (PAJs), and frequency variations. This article proposes a PLL independent frequency estimation technique. It estimates the frequency using the simplified teager energy operation on the normalized in-phase voltage component output of the SOGI. The phase-angle is estimated using the third-order polynomial approximated arctangent function on the in-phase and in-quadrature outputs of the proposed frequency-adaptive SOGI. The grid synchronization technique presented in this work avoids the use of any trigonometric operations and PLL gain tuning issues. Additionally, the impact of steady-state grid disturbances, namely, harmonics and dc offset on the proposed synchronization technique is investigated. Finally, its performance robustness is compared with other techniques during both grid transients and steady-state disturbances using both simulation analysis and experimental validation.