The accurate detection of phase and amplitude of the fundamental grid voltage is an important guarantee for the stable operation of three-phase grid-connected converters. In order to solve the problem of poor phase locking accuracy of the conventional phase-locked loop(PLL)based on single synchronous rotating coordinate when the grid voltage is distorted or unbalanced

this paper proposes a synchronization method of multi-resonant decoupled network based on the double second-order generalized integrator frequency-locked loop(DSOGI-FLL). Firstly

the principle of SOGI-FLL extracting fundamental voltage and frequency self-adaptively is studied. Secondly

the frequency-locked response characteristics of DSOGI-FLL under unbalanced power grid are analyzed in detail. Then a gain normalized linear model considering the negative sequence voltage component is proposed to improve frequency-locked performance of DSOGI-FLL under the unbalanced power grid. Based on the DSOGI-FLL

a resonant decoupled network with multiple second-order generalized integrators is designed to realize the accurate acquisition of fundamental voltage information under the distorted and unbalanced power grid. Finally

the results of simulation and experimental examples show that the proposed method is able to accurately obtain the phase and amplitude information of the positive sequence component of fundamental grid voltage when the grid voltage is distorted or unbalanced.