A grid synchronization PLL with accurate extraction technique of positive/negative sequences and DC-offset under frequency drift

This article proposes a delayed signal-based demodulation algorithm that enables a fast and accurate extraction of the positive/negative sequences and DC-offset in the grid voltage under a frequency drift. Moreover, a simplified mathematical formalism is proposed to reduce the computational burden for real-time implementation. The algorithm is incorporated with a third-order quasi-type-1 phase-locked loop (TQT1-PLL) to estimate the grid voltage instantaneous phase-angle and frequency. The performance of the proposed PLL referred to as delayed signal demodulation based TQT1-PLL (DSD-TQT1-PLL) is evaluated under highly disturbed grid voltage conditions including DC-offset, fundamental frequency negative sequence (FFNS), characteristic harmonics, and frequency variation. The obtained simulation and experimental results show that the proposed PLL can precisely estimate the frequency and the instantaneous phase-angle of the fundamental frequency positive sequence (FFPS) without any ripple. The results showed also its superiority over the conventional and adaptive QT1-PLLs, where a better dynamic response is obtained.