An Adaptive Enhanced Generalized Integrator-Based Complex Filter for Fundamental Components Extraction Under Weak-Grid Integrated Single-Phase Systems

Second-order generalized integrator (SOGI)-based phase-locked loop (PLL) and frequency-locked loop (FLL) are widely adopted in various applications such as grid voltage parameter estimation, synchronization, and control of grid-connected converters. However, it is highly sensitive to interharmonics or subharmonics and dc-offset. It causes unequal amplitudes in the quadrature signals and oscillatory errors and ripples in the estimated grid voltage amplitude, phase, and frequency. To address these challenges, this article proposes a frequency adaptive enhanced generalized integrator complex filter (eGICF)-based structure. The proposed method is designed to extract more accurate fundamental in-phase and quadrature-phase signals. It achieves significantly lower harmonics as 0.23% and 0.11%, respectively, even under the highly distorted grid voltage (22.27% THD). The proposed eGICF integrates a GICF with an improved SOGI (ISOGI) serving as an in-loop prefilter. The ISOGI first rejects dc-offsets, high-order harmonics, and producing complex signals. The GICF then refined and effectively rejecting low-order harmonics and interharmonics. The performance of the proposed frequency-adaptive eGICF-based quadrature signal generation (QSG) is evaluated and compared with existing architectures using MATLAB/SIMULINK under highly distorted and dc-offset grid conditions. In addition, the algorithm is implemented on a field-programmable gate array (FPGA)-based controller to validate its effectiveness experimentally under various nonideal grid conditions.