This paper deals with the study of shunt active filters used for suppressing particular
harmonics generated by nonlinear loads in utility distribution power systems. Both structures of shunt
active filter, voltage source active filter (VSAF) and current source active filter (CSAF), are
considered. The analytical study of specific harmonics identification in a given spectrum is first
presented. For simulation as well as experimentation the nonlinear load is a conventional three phase
thyristor rectifier and harmonics 5 and 7 are selected to be eliminated by active filter. The whole
system consisting of the ac power supply network, the SCR rectifier and the shunt active filter
(VSAF/CSAF) is then simulated. The simulation results are discussed and the efficiency of the two
kinds of active filter are compared. Finally, for the first structure, VSAF, the simulation results are
confirmed by experimental test realized by means of a fully digital control active power filter
developed in our laboratory.