As an important issue of the control algorithm for grid-connected inverters

the grid synchronization algorithm is critical to improve the control performance of grid-connected inverters. According to the design of the discrete Luenberger observer

a discrete complex-variable filter is designed to extract the sequence component. Moreover

regarding to the application of harmonics

a harmonic sequence component observer based on the structure of a multiple complex-variable filter is developed. The transfer process of the frequency error is analyzed when the input voltage frequency is different from the frequency parameter of the sequence component observer. Then the observation equation of input voltage frequency is designed

which enables the proposed sequence component observer to adapt to the change of grid frequency. In addition

an approximately linearized dynamic model is developed to facilitate the gain design of the frequency observation. Finally

simulations and experiments are carried out to verify the correctness and effectiveness of the proposed grid synchronization algorithm. The results show that the proposed algorithm is able to improve the dynamic performance of grid frequency observation while reducing the frequency observation time

and the application implementation is simple and effective with a small amount of calculation. This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2014AA052002)

the Cooperative Innovation Fund of Jiangsu Province—the Prospective and Joint Research Project(No. BY2015070-13)

and State Grid Corporation of China(No. 521820150005).