Performance improvement of a three‐phase PLL under distorted grid conditions based on frequency adaptive hybrid pre‐filtering

Abstract

The phase-locked loop (PLL) is widely used for grid synchronization in converter control. The moving-average filter (MAF)-based PLL has recently attracted considerable attention. However, the response time is drastically increased due to the MAF's large window width, determined by the lowest harmonics. Furthermore, the filtering performance of MAF is affected by frequency fluctuation. This paper presents an improved PLL with a hybrid pre-filtering, frequency-adaptive MAF-based PLL (FAMAF-PLL), ingeniously cascading the MAF and the dual-second-order generalized integrator frequency-locked loop (DSOGI-FLL). The DSOGI-FLL measures the frequency and filters out the lowest harmonics caused by the three-phase imbalance. Thus, the delay time of MAF is reduced by narrowing the window width, and the filtering performance of the MAF is greatly improved through frequency adaptation based on the DSOGI-FLL. The proposed FAMAF-PLL significantly enhances the performance and accelerates the dynamic response compared with MAF-PLL. Experiments were carried out to validate the effectiveness and robustness of the proposed method.