A Type-3 Modified SOGI-PLL With Grid Disturbance Rejection Capability for Single-Phase Grid-Tied Converters

This article presents a type-3 second-order generalized integrator phase-locked loop (SOGI-PLL) algorithm for single-phase system. Disturbances, such as dc offset and harmonics, are present in the practical grid voltages, due to occurrence of faults, sensors, and analog-to-digital converters. The type-3 SOGI-PLL exhibits fast dynamic performance with gain and phase-lead compensation. However, the general type-3 SOGI-PLL introduces fundamental frequency oscillations in the estimated quantities at the output, when grid voltage contains disturbances. The incorporation of filters for suppression of frequency oscillations, due to dc offset, reduces the bandwidth of PLL, which affects the dynamic response of PLL by introducing phase delay. Thus, a modified notch-filter SOGI (MNF-SOGI) based type-3 SOGI-PLL is proposed with frequency adaptive control to eliminate the phase error, without affecting the dynamic performance. A detailed analysis is presented on the effect of dc offset and scaling error. To enhance dynamic response, filtering, and stability designed guideline based on settling time is also discussed. The proposed type-3 MNF-SOGI-PLL has better grid parameter estimation and fast response with inherent dc offset rejection capability. The effectiveness of the proposed type-3 MNF-SOGI-PLL is evaluated under various grid disturbance conditions and experimentally verified.