This thesis studies a topology for reducing converter rating in hybrid active power filters (HAPFs).Technological advances in the production and use of semiconductor devices has led to the increasing of non-linear loads most of which receive non-sinusoidal current from grid. Flowing non-sinusoidal currents in power grids causes creating harmonics, and diffusion of these harmonics in system causes a lot of problems such as transformers and electric devices warming, burning fuse in the power factor correction capacitors and the possibility of harmonics’ level amplification due to series and parallel resonance phenomena. One the methods for controlling harmonics is use of power filters. Power filters generally divided into three category including passive, active and hybrid. Hybrid active power filters are made from combination of active and hybrid filters, and are designed in the way that maintain the advantages of both active and hybrid filters and minimize their disadvantages. One of the advantages of hybrid filters over the active ones is lower inverter power rating in hybrid structures. Nevertheless, further reduction of inverter power rating in hybrid power filters and thereby possibility of compensating loads with higher power is one of the raised research topics. First of all, several types of hybrid filters examined using the analytical relations and simulation and the level of inverter power rating of these structures taken into consideration specifically. Also mutual influence of passive and active parts on each other will be shown. Then a proposed topology for removing the fundamental current from inverter using three-coil transformer will be examined and its optimization will be discussed. In this way, in addition to reduce the size of active part of the hybrid filter, the number of passive elements are reduced as well, and the size of passive elements with regard to thequality factor of the passive filter and the amount of produced reactive power by filter will choose accurately. In the Considered control system for proposed hybrid filter, for generating appropriate reference current, coefficients are considered for the different types of harmonics which by use of optimizing algorithm PSO the exact amount of them will be calculated. According to the optimization process and to obtain a reduction of inverter power rating, current control of this type of filter take into consideration. To control current, finite states predictive current control which has shown a perfect quality in different applications of power electronic and drive, will be chosen. After introducing the method of finite states predictive current control, the results of its implementation on a three-phase inverter with common controllers will be compared. This method of control for proposed filter will be implemented and techniques for reducing the number of switching and also compensating the existing delay caused by the amount of calculations will be presented. After accurate examining of the proposed structure using simulation, practical results of implementation of the method of finite states predictive current control on the presented structure using a DSP TMS320F28335 processor will be calculated, and the results of simulation will compare with practical results and a good agreement between them will be shown. Keywords: Harmonic, Power filters, Active-Hybrid power filters, current control, Finite states predictive current control