Phase and frequency estimation for grid-connected inverters

Abstract

The controllers of three-phase grid-connected inverters usually require improvements to meet the stringent grid codes with the fault-ride-through (FRT) capability. Therefore, the performance of the grid-connected inverter depends on the quality of the selected phase-locked loop (PLL). This paper proposes a PLL method that has greater accuracy and better dynamics under an unbalanced and highly distorted voltage. The proposed method is based on the least squares technique using the Levenberg-Marquardt algorithm with adaptive initial parameters for rapid convergence to the solution. The simulated and experimental results under unbalanced and harmonic voltage validated the performance of the proposed method.