Digital filter suitable to connect renewable energy generation systems to the grid

In grid-connected renewable energy generation systems, it is convenient to synchronize the grid voltages with the current provided by the inverter; beside, in three-phase systems, also the inverter phases sequence must coincide with that of the grid. To this aim, the components of the grid voltage phasor, referred to a fixed reference frame, have to be calculated, starting by the measure of two line-to-line grid voltages. The paper proposes a suitable PLL filter allowing an accurate tracking of the grid voltages components, even if voltage harmonics and unbalanced grid voltages are present.