Grid Synchronization for Three-Phase Grid-Tied Converter Using Decouple-Second-Order Generalized Integrator

Abstract

As universally well known, the phase angle of the grid voltage is a crucial parameter to the control performance of the grid-tied power converters. This paper emphases on robust grid synchronization technique for three-phase grid-tied photovoltaic system in order to detect fundamental frequency, phase, and amplitude. However, the accuracy of the estimated frequency depends on the type of abnormal grid voltages and the structure of the phase-locked loop or frequency-locked loop control scheme. The widely accepted phase-locked loop (PLL) algorithm has a complex architecture and requires a tedious tuning process to obtain a good stability margin. Decouple-second-order generalized integrator-based frequency-locked loop (SOGI-FLL) is proven to have the most promising performance by eliminating both the negative and harmonic distorted components under non-ideal grid voltage conditions. Moreover, even in the absence of any PI controller, when the grid voltage has characteristics such as dips, swells, harmonics, unbalance, and frequency changes, it can accurately track the frequency of the grid voltage. The simulation results show that the proposed DSOGI-FLL is effective under all abnormal grid voltage conditions. The results are verified through experiments to prove the superior performance of DSOGI-FLL under adverse conditions.