Frequency Adaptive Prefiltering Stage for Differentiation-Based Control of Shunt Active Filter Under Polluted Grid Conditions

Abstract

A differentiation-based control method for a shunt active power filter is used in this paper for functioning in the presence of grid voltages distortion and imbalances. To enable the fast and accurate estimation of the variables in the presence of unbalancing or distortion in the grid voltages, a prefiltering scheme is considered based on the dual second-order generalized integrator approach. The signal recomposition performed by the prefilter isolates the harmonics from the voltage and current waveforms, and the differentiator frequency locked loop (dFLL) is able to estimate the frequency of the waveforms, which is used as a feedback for the prefilter, thus making the system frequency adaptive. The control algorithm is validated with both simulation studies. The prototype of an active power filter is developed, which carried out current compensation robustly, demonstrating the speed and accuracy of the system even under distorted grid conditions by achieved total harmonic distortions (THDs) of the grid currents within limits (less than 5%) as dictated by IEEE Std. 519-2014.