An Implementation of Improved PLL for Control of Grid-Connected Converters Under Grid Perturbations

In this article, a new method is proposed for calculating electric angle using a phase-locked loop (PLL) to perform these calculations correctly under disturbance conditions of the grid voltage. This work is based on using the decoupled double synchronous reference frame PLL (DDSRF-PLL), and this kind of PLL has been expanded to solve its problems in the presence of harmonics and high disturbance in the input voltage. In the DDSRF-PLL, only components with a frequency of double the fundamental frequency will be deleted, but in the expanded PLL all the harmonics will be eliminated. The effect of this method was tested using both simulation and practical experimentation. The simulation of this method was performed in MATLAB software. It has been shown that this method is robust, precise and fast for calculating the electric angle under grid voltage perturbations. Subsequently, the developed PLL was implemented in a FPGA-based experimental setup and its function was studied.