A second-order generalized differentiator method for eliminating DC component in the three-phase PLL for grid-connected inverters

This, paper proposes a method to eliminate the dc component in the measured three-phase grid voltage as the input signals of phase-locked loop (PLL). The dc component in the input signals of PLL causes a low-frequency oscillation of grid frequency. The dc component elimination can be achieved by replacing the integrator in the second-order generalized integrator (SOGI) with a differentiator, named as second-order generalized differentiator (SOGD). The good performance of a proposed SOGD is validated with experimental results with 32-bit DSP by using unbalanced three-phase signals with dc components.