Advanced Grid Synchronization Scheme Based on Dual eSOGI-FLL for Grid-Feeding Converters

In this article, an improved grid synchronization method for three-phase grid-feeding converters using a dual enhanced second-order generalized integrator (eSOGI) frequency-locked loop (FLL) is proposed. The eSOGI, of which gains can be adjusted based on the positive-sequence component of the grid voltage, is designed to estimate the grid voltage accurately. Moreover, to improve the grid frequency estimation under grid voltage sags, frequency rate limits is suggested in the FLL structure. The selection of the eSOGI-FLL parameters is described as well. After the estimated grid voltages are obtained using the dual eSOGI-FLL, they are used to synthesize the references in the dual-current controllers for positive- and negative-sequence components. Through the simulation and experimental results under grid voltage sags and distorted grid conditions, the improved power control performance of the proposed method has been demonstrated in comparison with those of the existing methods.