Grid harmonics and voltage unbalance effect elimination for three-phase PLL grid synchronization algorithm

The conventional synchronous reference frame phase locked loop (SRF-PLL) works perfectly for synchronization of utility interactive systems with grid that has no imperfections such as harmonics, unbalanced voltage or frequency fluctuation. However, the power grid suffers from these types of imperfections. For large distributed systems such as solar, onshore and offshore wind or wave energy, there is a need for synchronization with the frequency and phase angle of the three-phase grid contaminated with harmonics. For three-phase systems, the other imperfection of the grid that needs to be eliminated before feeding the grid voltage to PLL is the voltage unbalance. The proposed algorithm demonstrates a method to eliminate both the three-phase grid voltage harmonics and unbalance effects to improve the steady state performance of grid synchronization with high bandwidth PLL.