Variable Window Size Moving Average Filter for Phase-Locked-Loop Synchronization

Abstract

Efficient grid synchronization is crucial for integrating renewable energy sources and Flexible AC Transmission systems (FACTs) into power grids. This paper addresses the challenges faced by Synchronous Reference Frame Phase-Locked Loops (SRF-PLLs) in harmonic-polluted grids and proposes a novel solution employing Moving Average Filters (MAFs). The conventional MAF-PLL with a fundamental period window size provides harmonic rejection but slows down the dynamic response. To enhance MAF-PLL performance under harmonic-polluted grid conditions, we introduce a Variable Window Size (VWS) MAF. The proposed VWS-MAF adapts its window size based on the dominant frequency of oscillation in the dq frame, determined using Short-Time Fourier Transform (STFT). The proposed method ensures minimum window size, based on grid conditions, which improves the dynamic response while maintaining harmonic rejection capabilities. The proposed method offers improved adaptability and promising performance in elimination of integer harmonics, DC offset, interharmonics, and negative sequence component. Simulation and experimental studies are presented that demonstrate the effectiveness of VWS-MAF, positioning it as a noteworthy advancement in PLL technology for robust grid synchronization.

Keywords

• Grid synchronization
• harmonic rejection
• moving average filters (MAFs)
• phase-locked loops (PLLs)
• short-time Fourier transform (STFT)
• variable window size (VWS)