A Three-Phase Frequency-Adaptive Phase-Locked Loop for Independent Single-Phase Operation

This letter proposes a phase-locked loop (PLL) able to operate as an independent single-phase PLL in the context of three-phase systems. Its key advantage is that the extracted information allows the independent control of both the active and reactive powers for each phase. The proposed PLL utilizes moving average filters and, hence, remains robust under unbalanced and highly distorted voltages. A frequency estimator is also presented and incorporated in the PLL angle detector path to make it frequency adaptive. The performance of the proposed PLL is verified experimentally and results for frequency change, phase-angle jump, and unbalanced voltage sag are reported as a confirmation of its potential.