Impedance Analysis of SOGI-FLL-Based Grid Synchronization

The latest research has pointed out that the Phase-Locked Loop (PLL) plays an important role in shaping the impedance of grid-connected converters, yet most of the works so far merely focus on the synchronous reference-frame PLL. Alternatively, this letter presents the impedance analysis of the Second-Order Generalized Integrator Frequency-Locked Loop (SOGI-FLL), which has been introduced for realizing grid synchronization in the stationary reference frame. The influences of the voltage perturbation on the estimated phase and further on the output current are revealed for the grid-connected converter using the SOGI-FLL. The frequency coupling effect of the SOGI-FLL is also identified and verified in the experimental tests.