This paper deals with three-phase four-wire shunt active filter to improve power quality. It proposes backstepping control based on Lyapunov theory for the filter dc side voltage, and a modified synchronous reference frame approach based on two selftuning filters for the identification of harmonic currents. The voltage source inverter of shunt active filter has a four-leg twolevel topology. It is controlled by hysteresis. The proposed shunt active filter is verified by simulation and experimental validation. Backstepping control, an approach for nonlinear systems, leads to good dynamic and static performance in the dc side voltage control. Three-phase four-wire shunt active filter using the modified synchronous reference frame approach reduced the total harmonic distortion in the tested operating conditions.

Keywords: Backstepping controller, Self-tuning filter, Synchronous reference frame, Three-phase four-wire shunt active filter, Total harmonic distortion (THD)