A frequency-locked loop technology of three-phase grid-connected inverter based on improved reduced order generalized integrator

The quality of grid-connected current is an important index to measure the performance of grid-connected inverter, rapid and accurate detection of the grid frequency and phase is the premise of the grid-connected current control. A method of the frequency-locked loop (FLL) based on improved reduced order generalized integrator (here called ROGI-FLL) is proposed based on the present FLL technology in this paper, which is able to extract the positive and negative sequence components of the grid voltage and frequency under the condition of unbalanced grid, harmonic distortion, direct current offset and so on. The ROGI-FLL method is used in the grid-connected current control strategy without phase-locked loop, finally the feasibility and effectiveness of this method are verified by simulation and experiment.