An advanced hybrid pre-filtering/in-loop-filtering based PLL under adverse grid conditions

Abstract

The amplitude, frequency and phase angle of the grid voltage are essential three components to ensure synchronization for grid interactive inverters. Synchronous reference frame-phase locked loop (SRF-PLL) is widely used to obtain these components. Although the SRF-PLL shows a perfect performance under ideal grid conditions, its performance deteriorates under unbalanced and distorted grid conditions. Therefore, researchers have been working to provide more advanced PLL methods. A dual third order generalized integrator PLL (DTOGI-PLL) and quasi-type-1 PLL (QT1-PLL) are two PLL methods that have come to the fore in grid synchronization recently. As with any method, these PLL methods have both advantages and disadvantages. The aim of this study is to integrate the advantages of the two methods, and to develop a new PLL method with better performance than these two methods. It means that the proposed PLL has the adaptive filtering capability of the DTOGI-PLL and fast transient response of the QT1-PLL. The effectiveness of the proposed PLL is confirmed by experimental results. The experimental results demonstrate that the proposed PLL is a more effective method than the DTOGI-PLL and QT1-PLL under adverse grid conditions.