DC offset rejection and harmonics filtering improvement in second-order generalized integrator based-phase-locked loop: A comprehensive review

The high penetration of renewable energy sources (RESs) has increased the integration of power electronics devices into the power grid. Therefore, a fast and accurate grid synchronization method is necessary to maintain acceptable performance under abnormal conditions such as phase disturbances, frequency oscillations, voltage sag/swell, harmonics, and DC offset. The phase-locked loop (PLL) is the most widely used method for grid synchronization due to its simplicity and robust performance, which has increased the popularity of PLL-based orthogonal signal generation (OSG) in synchronization applications. In practical implementation, the PLL-based second-order generalized integrator (SOGI) is widely used in single-phase systems because of its simple structure, frequency adaptability, and filtering capability. Hence, this paper comprehensively reviews several advanced SOGI-based PLLs, focusing on their main characteristics, control methods, and performance indices, such as settling time, percent overshoot, and the peak of the estimated phase and frequency. Additionally, the advantages and disadvantages of existing PLLs are summarized, including their ability to reject DC offset and filter harmonics. This review aims to provide researchers with a deep understanding of the merits and limitations of SOGI-PLLs, paving the way for further contributions to the field.