Grid Synchronization Techniques Analysis of DG Systems Under Grid Fault Conditions

The integration of renewable energy sources (RES) and their connection to actual transmission power grids around the world at a range of voltage levels has recently gained a significant penetration level. The changes brought by these alternative power sources have an important impact on system performance and efficiency in terms of the quality and the stability of the existing grid, which is not yet dedicated to meet the modern grid code requirements. One of these vital requirements is synchronization with the grid voltage which is achieved by the synchronization unit of the grid side converter (GSC) controller. The synchronization unit usually consists of a phase-locked loop (PLL) algorithm to track the phase angle and amplitude of the grid voltage at the point of common coupling (PCC). This paper analyzes respectively the synchronization capability of four PLL techniques for distributed generation system (DGS) during balanced and unbalanced faults: the synchronous reference frame PLL (SRF-PLL), stationary reference frame PLL (αβ-PLL), decoupled synchronous reference frame PLL (DSRF-PLL), and the recent decoupled stationary reference frame PLL (Dαβ-PLL). The different considered algorithms are presented, analyzed, compared, and their performance is simulated and carried out using MATLAB/SIMULINK.