In this thesis, after a survey on harmonic problems and different harmonic mitigation techniques, Hybrid Active Power Filters (HAPFs) are studied. HAPFs are a newer kind of filters used to control harmonics in power systems. These filters are made by combining passive and active filters to prevent resonance of passive filter while obtaining better filtering quality with a small rated inverter. An introduction to passive and active filters is given and some methods used to combine these filters are discussed. There are two commonly-used types of HAPFs: the first is an active part in series with power source in addition to a parallel passive filter, the second one, or parallel HAPF, is a series combination of an active and a passive part installed in parallel to the load. Different control approaches for these common types are presented. With mathematical equations using circuit theory in addition to time-based simulations, these common HAPFs are compared together. Reasons for more trends in using the parallel HAPF are discussed. The parallel HAPF is chosen for more studies especially in control methods. Since in most cases parallel filters are used to inject (or sink) current harmonics, a current control technique which is based on current prediction by using the load model is studied. There is a chapter on this approach which is named Finite States Predictive Current Control. This current control technique has been used in different power electronics and electric drives applications and has shown very good performance. The method is discussed for current control of single- and three-phase loads. A laboratory model is used to verify the method in practice by using a TMS320F28016 Digital Signal Processor (DSP) unit. Some methods are proposed to simplify calculations for the DSP unit. In addition, a technique to estimate the unknown model in practice is proposed and implemented. The method can estimate the model by applying test signals (inverter output voltage) and reading the output (load current). Signal filtering is an indispensable part of active filtering. There are two common filters used to extract a single frequency from a signal. Single frequency filtering by using the Synchronous Rotating Frame (SRF) and the Instantaneous p-q Theory are the most commonly used methods that are discussed and compared together, also their similarities are shown in block diagrams. rated inverter is enough for current control. The simulation results Keywords: Hybrid Power Filter, Finite States Predictive Control, Digital Signal Processor (DSP), Unified Control, Instantaneous p-q Theory, Filtering by Using Synchronous Reference Frames
