Authors: S. Golestan, J. M. Guerrero, Y. Al-Turki, A. M. Abusorrah and J. C. Vasquez
With the ever-increasing penetration of power electronics converters into power systems in recent years, grid connection codes have enforced more stringent requirements on these converters. Fulfilling these requirements using the phase-locked loop (PLL) concept, which is currently the central concept in designing grid synchronization systems, can sometimes be challenging. To improve the speed/accuracy trade-off of closed-loop synchronization systems (especially PLLs), designing open-loop synchronization (OLS) systems for grid-tied power converters has received attention recently. This article provides a unified summary of recent progress in designing OLS systems. It shows that recent contributions in designing filtering stages and correction systems, which are the key elements of OLS algorithms, are mostly equivalent (or, at least, very similar) concepts/methods. Based on these findings, different OLS systems are combined into some general structures as shown below and comprehensive design guidelines are provided. Directions for future research in the area are also provided in the article.
All in all, in scenarios where an improved speed/accuracy tradeoff is required, an OLS algorithm (if designed wisely) might be advantageous over a PLL and therefore deserves to be considered/investigated as an alternative.