Phase locked loop based on an observer for grid synchronization

Grid synchronization technique is essential for grid-connected power converters. Phase locked loop (PLL) has been exploited as an implementation technique. However, additional efforts are required for PLL to deal with severely distorted grid voltages. In this paper, an observer is proposed to enhance the performance of PLL. A state equation is formulated to extract positive-sequence voltage from the distorted grid voltage and is utilized to construct the observer. Guidelines are suggested to set the gains of the observer along with its internal transfer functions. The PLL combined with the proposed observer has been tested in simulations and experiments in contrast to dual second order generalized integrator frequency locked loop (DSOGI-FLL). The results have validated that the proposed method reveals better phase-tracking performance for grid synchronization.