Robust grid synchronisation in three-phase distributed power generation systems by synchronous reference frame pre-filtering

In this paper a synchronous reference frame three-phase phase-locked-loop (PLL) is considered, suitable for distributed power generation systems, e.g. photovoltaic or wind power converters. Digital pre-filtering of measured voltages within synchronous frame and based on a bank of multiple notch filters is proposed in order to enhance immunity to non-ideal condition of the grid and raise the dynamic performance of the loop with respect to classical filtering solution in the three-phase reference frame. Detailed analytical derivation of the different harmonic components generated by grid non-ideal components is fully analysed in order to define specifications on the notch filters. More general results are obtained as compared to literature. Extensive simulation results is presented accounting for actual digital implementation and considering limitations on voltage harmonics and unbalance imposed by standard regulations, demonstrating better overall performance as compared to state-of-art proposals.