A new phase-locked loop algorithm with ECCF-MAF under unbalanced grids

With the large-scale integration of distributed energy resources and the widespread application of nonlinear loads, the problem of three-phase unbalance in the power grid has becoming more and more serious. The phase-locked loop (PLL) method should improve its performance of synchronization accuracy and dynamic response. A new PLL algorithm based on an enhanced complex coefficient filter (ECCF) and a moving average filter (MAF) is proposed in this paper. Based on the PLL effect analysis of unbalanced grids, by deriving the relationship between model parameters and frequency, the ECCF can correct the model parameters in real time. And MAF achieve high-precision filtering through a fixed window length, ensuring the dynamic response speed. With ECCF and MAF, the problem of frequency fluctuations and harmonic disturbance is solved. To verify the performance of the proposed ECCF-MAF method, MATLAB/Simulink simulation are carried out under different unbalanced grid conditions. For conditions such as grid voltage distortion and harmonic disturbance, the ECCF-MAF method can quickly extract the positive sequence voltage component, suppress the influence of low-order harmonics. The results show that compared with the traditional PLL method, the proposed ECCF-MAF method significantly reduces the synchronization error and greatly improves the response speed when tracking the grid. And the proposed PLL provides a more robust synchronization control solution for the new energy grid-connected system.