A three-phase adaptive phase-locked loop scheme for utility grid-connected systems

This paper deals with a phase-locked loop (PLL) algorithm for both phase-angle and frequency detections in three-phase utility grid connected systems. The proposed algorithm uses non-autonomous adaptive filters (AFs) for extracting the fundamental components of the utility voltages, while a positive sequence detector (PSD) is employed for obtaining the positive sequence components at fundamental utility frequency. Both the AFs and the PSD operate in conjunction with a three-phase power-based PLL (3pPLL) yielding the scheme called AF-PSD-3pPLL. Therefore, power quality problems that interfere on the PLL performance are mitigated, such as voltage harmonics and unbalances. The performance of the proposed AF-PSD-3pPLL algorithm is evaluated by means of experimental tests considering utility disturbances, such as voltage harmonics, voltage unbalances, and voltage sags.