Frequency-Adaptive Observer to Extract AC-Coupled Signals for Grid Synchronization

In three-phase grids, the grid synchronization has been widely discussed with mainly focusing on the mitigation of low-order harmonics and unbalances. In this paper, the elimination of a dc bias is also considered in the process of the grid synchronization. Because the proposed method is based on a frequency-adaptive observer, it can maintain its performances even if the fundamental frequency is changed. The state equation is newly established for the observer, and its gains are discussed in terms of their influences to the filtering performances. The effectiveness of the proposed method is assessed with various simulations and experiments.