I. Introduction
Power quality control has become a critical issue in modem electrical networks. A variety of Flexible AC Transmission system related equipments [1]–[6] have been developed in the past years to serve for power quality purposes such as: Active and Hybrid power filter, Static compensator (STATCOM or DSTATCOM), Static Var Compensator (SVC), Unified Power Flow/Quality Controller (UPFC/UPQC), Dynamic Voltage Restorer (DVR). In particular, active powers filters have the potential to offer “controlled” harmonic reduction and power quality improvement on power systems. However, the accurate management of active filters [7] is a demanding control challenge, as high bandwidth regulation is required using a reasonable switching frequency, and in the presence of supply disturbances [8], [9].