Improved phase-locked loop under heavily distorted grid condition

This paper proposes a novel phase-locked loop (PLL) for grid synchronization based on the moving average filter (MAF) and the weighted least squares estimation (WLSE) scheme, namely WLSE-PLL. The MAF can eliminate all the odd-order harmonics and the fundamental negative-sequence component. The WLSE is employed to estimate the fundamental positive-sequence component (FPS). Combining the zero crossing detection (ZCD) and the frequency locked-loop (FLL), the WLSE-PLL is also adaptive to frequency deviation. Through analysis and simulation, the WLSE-PLL is proved to have a fast response and a satisfactory performance even under heavily distorted grid conditions including three-phase unbalance, dc offset and harmonics.