Suppression of harmonic distortions in second order generalised integrator based PLLs for grid connected converters

This paper investigates the effect of harmonic distortion in the utility voltage on the performance of the widely used second order generalised integrator (SOGI) based phase locked loop (PLL). An analytical method that estimates the PLL output harmonics due to harmonic distortions in the utility grid is presented and the results of the analytical method are compared to time domain simulations. Furthermore, two modified SOGI PLL structures are proposed which offers significant performance improvement over the conventional SOGI PLL in terms of harmonic rejection capability.