A Zero-Tracking SOGI-Based Frequency-Locked Loop

This article proposes a zero-tracking second-order generalized integrator-based frequency-locked loop (ZT-SOGI-FLL) with better dynamics and stability than the conventional SOGI-FLL. Unlike the internal model principle, the ZT-SOGI-FLL reconstructs the input signal under frequency deviation by tracking the zeros. Also, it has the same compact structure as the conventional SOGI-FLL. A linearized model is then derived to show that the ZT-SOGI-FLL is always an over-damped or a critical damper system. More importantly, the derived model proves that ZT-SOGI-FLL has a larger damping factor and higher bandwidth than SOGI-FLL when the same SOGI gain is tuned. Finally, the input-to-state stability of ZT-SOGI-FLL is analyzed to support the high robustness to severe grid faults. Comparative experimental results show that ZT-SOGI-FLL has a faster and smoother dynamic response with a higher stability margin than some commonly used SOGI-based methods under grid faults.