Quasi Type-1 PLL With Tunable Phase Detector for Unbalanced and Distorted Three-Phase Grid

Out of various moving average filter (MAF)-based phase-locked-loop (PLL), quasi type-1 PLL (QT1-PLL) is widely adopted due to its fast dynamic performance, implementation simplicity, and harmonics rejection abilities. However, the performance QT1-PLL deteriorates in presence an off-nominal frequency unbalanced grid voltage component. Moreover, sensitivity towards fundamental negative sequence (FFNS) component high. Hence, this paper proposes a novel enhanced solution that insensitive unbalance signal during conditions. The proposed adaptive phase detector makes it possible estimate both positive (FFPS) FFNS components with high degree immunity against harmonics. Notably, pre-loop separation FFPS helps suppress second harmonic oscillations for improving parameter estimation accuracy. loop-filter design remains unaffected requires proportional gain information. To address DC offset issue, modified delayed cancellation method also proposed, which can theoretically eliminate any arbitrary delay length. A small-signal model developed sake stability analysis. Comparative numerical simulation experimental results are provided variants QT1-PLLs demonstrate improvement achieved technique.