Phase-Locked Loop (PLL) Techniques for Grid Synchronization: A Comprehensive Review

The increasing penetration of renewable energy into the grid necessitates the employment of grid synchronization techniques to ensure proper integration and stability of the system. Several grid synchronization techniques are available, among which the Phase Locked Loop(PLL) method has proven to be the more employed one owing to its simplicity and robustness. Despite being able to provide effective operation of the system under variable grid conditions this technique faces certain technological challenges. This paper studies, in detail, the various PLL techniques that are implemented in the Renewable Energy Sector(RES) such as Synchronous Reference Frame (SRF PLL), Decoupled Double Synchronous Reference Frame (DDSRF PLL), Enhanced Phase Locked Loop (EPLL), and Dual Second Order General Integrator (DSOGI PLL). The different techniques of the PLL are compared and analyzed based on their efficiency, response to voltage and frequency deviations, complexity, and stability. SRF PLL gives excellent response under balanced grid conditions, but EPLL, FLL and SOGI based PLLs are more efficient to address unbalanced grid conditions. The limitations of the PLL technique such as reduced stability margin and manufacturing costs, has lead to the development of improved and new PLLs, which are under research.