Delay Analysis and Compensation for Digital MSOGI-QSG Implementation in Back-to-Back Interfacing Converter Between Microgrid and Utility Grid for Harmonic Extraction

Abstract

Due to its ability to detect different harmonic components in highly polluted grid conditions and harmonics induced into the microgrid point of common coupling (PCC) bus by nonlinear loads, the multiple second-order generalized integrator-quadrature signal generator (MSOGI-QSG) is widely used in domains like grid synchronization and signal extraction. However, it typically suffers from an ac discretization error problem in digital implementation. The impact of unit delay in cross feedback to break algebraic loops in digital implementation is investigated in this paper, and it is discovered that uncompensated delay causes steady-state errors even if individual second-order generalized integrator-quadrature signal generator (SOGI-QSG) discretization is accurate. Based on the findings, a simple and effective rotational transformation-based compensation method is proposed, which considerably enhances the accuracy of signal extraction and frequency estimation when used in conjunction with a frequency-locked loop (FLL). The proposed method is validated through experimental results.