Performance Investigation of Modified Second Order Generalized Integrator Based Phase Locked Loops for a DC Offset Perturbed Grid

Nowadays, there is a lot of concern about ensuring that three-phase grid-connected Renewable Energy Sources (RES) are properly synchronized. Key elements, including the utility voltage's frequency, amplitude and phase, are essential for appropriate synchronization of the grid-connected inverters. These factors are correctly determined in a Synchronous Reference Frame Phase Locked Loop (SRF PLL) under a perfect grid condition. However, its performance gets worse in the presence of unbalanced or distorted grid conditions. As a result, there is a budding need for extremely efficient and accurate PLL system, for example the Dual Second Order Generalized Integrator PLL (DSOGI PLL), for grid synchronization. However, DSOGI PLL is not able to precisely estimate the phase when DC offset is present in the grid voltage, which calls for additional modifications. In order to find a better PLL with improved performances regarding adaptive filtering, DC rejection, and quickest transient response, this work explores enhanced PLLs based on SOGI filter modifications and evaluates their benefits and drawbacks. The effectiveness of these enhanced PLLs is analysed and validated through MATLAB/Simulink simulations under grid conditions affected by a DC offset.