Determination of Voltage References for Series Active Power Filter Based on a Robust PLL System

Power quality (PQ) is one of the most important issues of modern electrical distribution. The series active filter can play a very significant role in the correction of PQ problems such as voltage unbalance, sag, interruption and voltage harmonics. This paper deals with the determination of voltage references for series active power filter based on a robust three-phase digital locked loop (PLL) system. Whatever the nature of supply voltages perturbation, the PLL block allows to extract fundamental positive sequence voltages system on the common coupling point and to estimate the mains frequency. Various regulators PI, RST and fuzzy logic are studied and compared in order to assure good reliability, a fast tracking performances and a good attenuation of undesirable frequencies. The robustness of the regulators allows the PLL operating under non ideal conditions and provides good results under unbalanced and/or distorted supply voltages conditions. Simulation results are presented to confirm the validity of the proposed design.